Set Heat Device Requirements - Middle School Physical Science

Which term describes how well a thermal-control device meets its intended goal: criterion or constraint?

Criterion. Criteria measure success; constraints limit options.
Which option is a criterion: "must be safe to touch" or "must use cardboard only"?

Must be safe to touch. Safety is a performance goal, not a limitation.
What is a common safety constraint for a device that controls thermal energy transfer?

Surface temperature must stay below a safe limit. Prevents burns and ensures user safety during operation.
Choose the heat-transfer mode mainly reduced by adding foam insulation to the sides of a hot container.

Conduction. Foam blocks heat flow through solid materials by direct contact.
What is radiation (in the context of thermal energy transfer devices)?

Thermal energy transfer by electromagnetic waves. No medium needed; heat travels as infrared waves through space.
Which surface property is a key criterion when designing to reduce radiative heat transfer?

Low emissivity (shiny, reflective surface). Reflective surfaces bounce radiation rather than absorbing it.
What design feature most directly reduces convective heat transfer through an opening?

Seal gaps to prevent air movement (reduce fluid flow). Convection requires moving fluids; stopping flow stops heat transfer.
What surface property most directly reduces heat transfer by radiation?

Low emissivity, reflective surface (shiny). Shiny surfaces reflect thermal radiation rather than absorbing it.
Which term names the measurable goal: "Keep contents between $20\,^{\circ}\mathrm{C}$ and $25\,^{\circ}\mathrm{C}$ "?

Criterion. Criteria specify measurable targets the design must meet.
Which statement is a criterion rather than a constraint: "must be safe to touch" or "must use cardboard only"?

Must be safe to touch. Safety is a performance goal, not a resource limitation.
Choose the best design choice to reduce radiation: shiny foil wrap or black matte paint on the outside?

Shiny foil wrap. Reflective surfaces minimize radiation absorption and emission.
Which design feature most directly reduces convection in a container: sealed lid or metal wall?

Sealed lid. Prevents air movement, stopping convection currents.
What is one clear, measurable criterion statement for keeping contents warm in a lunch container?

Keep contents above a target temperature for a set time. Specific and measurable, making it a clear design goal.
What property of a material should be specified to control conduction through a device?

Thermal conductivity (high to transfer, low to insulate). Materials with low $k$ values resist heat flow; high $k$ values promote it.
What is the meaning of a design constraint when building a device to control thermal energy transfer?

A limit on the design, such as cost, size, time, or materials. Constraints restrict what you can use or do in your design.
Which term means "how well the device reduces heat transfer": criterion or constraint?

Criterion. Performance goals are criteria; limitations are constraints.
What is a common environmental constraint for selecting materials in a thermal-control device?

Materials must be non-toxic and environmentally safe. Protects users and environment from harmful substances.
Which material property is the key criterion when selecting an insulator to reduce conduction?

Low thermal conductivity. Insulators resist heat flow through poor particle-to-particle transfer.
What is the typical criterion statement format that makes a heat-control goal measurable and testable?

A specific temperature change over a specific time under stated conditions. Quantifiable goals allow objective testing of device performance.
What surface property most directly increases absorption of thermal radiation from sunlight?

High absorptivity, dark or matte surface. Dark surfaces absorb more electromagnetic radiation than light ones.
Identify the dependent variable when testing insulation thickness on heat loss.

Temperature change or rate of heat loss. The measured outcome that changes based on insulation thickness.
Choose the best design choice to increase conduction for cooling: metal plate or foam pad in contact with the object?

Metal plate. Metals conduct heat rapidly compared to insulators like foam.
Which statement is a constraint, not a criterion: "Mass must be under 1 kg" or "Minimize heat loss"?

Mass must be under $1\ \text{kg}$ . Sets a limit that cannot be exceeded, not a goal to achieve.
Which design choice reduces convection most directly: sealing air gaps or adding a metal rod connection?

Sealing air gaps. Prevents air movement that carries heat.
What is the meaning of a design constraint when building a device that controls heat transfer?

A limit on the design, such as cost, size, mass, time, or materials. Constraints restrict what you can use or do in your design.
Which option is a constraint: "mass must be less than $0.50\,\text{kg}$ " or "minimize heat loss"?

"Mass must be less than $0.50\,\text{kg}$ ". Mass limit is a restriction, not a performance goal.
Which term refers to the limit: "Must cost less than $20 to build"?

Constraint. Limits are constraints; this restricts the budget.
What surface property is most important for reducing heat transfer by radiation?

Low emissivity, shiny or reflective surface. Reflective surfaces bounce electromagnetic waves instead of absorbing them.
What is the meaning of a design constraint for a device that controls thermal energy transfer?

A limit on the design, such as cost, size, materials, or safety rules. Constraints restrict design choices and set boundaries.
Which statement is a constraint rather than a criterion: "reduce heat loss" or "use only $2$ sheets of foil"?

Use only $2$ sheets of foil. Material limits restrict design options, unlike performance goals.
Which material type is typically chosen to increase conduction: conductor or insulator?

Conductor. Conductors allow easy heat flow through their structure.
Which change reduces conduction in $\dot{Q}=\frac{kA\Delta T}{L}$ : decrease $k$ or increase $A$ ?

Decrease $k$ . Lower thermal conductivity ( $k$ ) reduces heat flow rate.
What is the most appropriate criterion statement format for thermal control performance?

A measurable goal with a quantity, unit, and test condition. Effective criteria must be specific and testable.
What is the main purpose of listing criteria and constraints before building a thermal-control device?

To define how success is measured and what limits the design must obey. Clear goals and limits guide effective design decisions.
What surface property most directly reduces thermal radiation emitted from a hot object?

Low emissivity, shiny or reflective surface. Shiny surfaces reflect rather than emit thermal radiation.
What is the primary criterion for a thermal-control device intended to keep an object cold?

Minimize heat gain into the object. Cold objects need protection from environmental heat.
What is a realistic safety constraint for a device that contains very hot or very cold objects?

External surface temperature must be safe to touch. Prevents burns and ensures user safety during handling.
What is the best criterion type to include if you must compare prototypes fairly for heat control performance?

A quantitative metric (temperature change or heat loss rate). Numbers allow objective comparison between different designs.
Which option is a criterion: "cost must be under $10" or "reduce heat transfer rate"?

"Reduce heat transfer rate". Heat transfer reduction is a performance goal.
Identify whether this statement is a criterion or constraint: "The device should keep water above $50^\circ\text{C}$ ."

Criterion. Temperature maintenance is a performance goal to achieve.
What is a common materials constraint when building a thermal control device for a classroom project?

Use only approved, available materials (for example, cardboard, foil, tape). Restricts choices to what's accessible in the classroom.
What is the correct formula for temperature change used in thermal criteria, using initial and final temperatures?

$\Delta T = T_f - T_i$ . Subtracts initial from final to show temperature increase or decrease.
What is one valid constraint related to cost when designing a thermal-control device?

Total material cost must be below a stated budget limit. Budget constraints limit material selection and design complexity.
What is an example of an environmental constraint that affects thermal device design?

Ambient temperature, wind, or humidity limits performance. External conditions create design limitations beyond control.
What is radiation in the context of controlling thermal energy transfer in a device?

Thermal energy transfer by electromagnetic waves. No medium needed; heat travels as infrared waves.
Which option is the best measurable criterion: "Works well" or "Limits temperature change to $\le 2\,^{\circ}\text{C}$ per hour"?

Limits temperature change to $\le 2\,^{\circ}\text{C}$ per hour. Specific, measurable goals are better criteria than vague statements.
Which term means a required condition the design must meet: criterion or constraint?

Constraint. Constraints are requirements that must be satisfied, not optional goals.
What criterion states a maximum allowed heat gain: "Temperature increase must be less than $5\,^{\circ}\mathrm{C}$ "?

Temperature increase must be less than $5\,^{\circ}\mathrm{C}$ . Sets a specific, measurable limit on thermal performance.
What safety constraint is most directly related to a device that controls thermal energy transfer?

Surface temperature must not cause burns. Prevents injury from hot surfaces during normal use.
Identify the constraint in this statement: "Keep a drink above $50^ $ for $30$ minutes."

For $30$ minutes. This time limit restricts the design.
Identify whether "Total mass must be less than $0.50\,\text{kg}$ " is a criterion or a constraint.

Constraint. Mass limit restricts design options, not performance goals.
What is the key safety constraint often applied to devices that manage heat transfer?

Prevent burns or overheating; exterior must stay at a safe temperature. User safety limits maximum surface temperatures.
What is the definition of radiation as a mode of thermal energy transfer?

Thermal energy transfer by electromagnetic waves. No medium needed; energy travels as infrared waves.
Which design feature most directly reduces convection: sealing air leaks or using a shiny surface?

Sealing air leaks. Prevents air movement that carries heat away.
Which design choice most directly increases conduction for heat removal: copper plate or foam layer?

Copper plate. Copper's high conductivity rapidly transfers heat.
Which term describes a measurable goal like "keep water above $50\,^{\circ}\mathrm{C}$ for 1 hour": criterion or constraint?

Criterion. Criteria are measurable goals; constraints are limitations.
Which surface property is most directly used as a criterion for reducing heat transfer by radiation?

Low emissivity or reflective (shiny) surface. Shiny surfaces reflect infrared waves instead of absorbing them.
What is the term for a design requirement stated with numbers and units (for example, $\Delta T \le 5\,^{\circ}\mathrm{C}$ )?

A measurable (quantitative) criterion. Uses numbers to specify exact performance targets.
Which term names the limit: "Total cost must be less than $10" for a thermal-control device?

Constraint. Constraints set boundaries on what can be used or done.
Which surface property is a key criterion when designing to reduce radiative heat transfer?

Low emissivity (shiny, reflective surface). Reflective surfaces bounce electromagnetic waves instead of absorbing them.
Which option is a measurable criterion: "keep water warm" or "keep water above $50\,^{\circ}\text{C}$ for 30 min"?

Keep water above $50\,^{\circ}\text{C}$ for 30 min. Specific values make criteria testable and measurable.
Which term describes a restriction that can prevent an ideal thermal-control design: criterion or constraint?

Constraint. Constraints impose limits on what can be designed.
Which option is a criterion: "must use only recycled materials" or "reduce heat transfer rate"?

"Reduce heat transfer rate". Heat transfer reduction is a performance goal, not a limitation.
Identify the constraint in this statement: "The device must fit inside a box of volume $1\,\mathrm{L}$ ."

Must fit inside a box of volume $1\,\mathrm{L}$ . This limits the physical dimensions allowed for the design.
Which thermal transfer mechanism is transfer by motion of a fluid such as air or water?

Convection. Moving fluids carry thermal energy with them.
Which term names a measurable target such as "keep contents above $50\,^{\circ}\text{C}$ for 2 hours"?

Design criterion. Criteria specify measurable performance goals, not limitations.
What is conduction (in the context of thermal energy transfer devices)?

Thermal energy transfer through direct contact between particles. Heat flows when particles collide and transfer kinetic energy.
Which criterion is most appropriate for a lunch cooler meant to keep food cold for $4\ \text{h}$ ?

Maintain internal temperature below a target for $4\ \text{h}$ . This goal specifies measurable performance requirements.
Identify whether "mass must be less than $1.0\,\text{kg}$ " is a criterion or a constraint.

Constraint. Mass limits restrict design options, making this a constraint.
Which constraint category best matches "must not contain toxic chemicals" for a heat-control device?

Safety constraint. Safety requirements limit material selection.
Identify the constraint in this requirement: "The device must fit inside a $10\,\text{cm} \times 10\,\text{cm} \times 10\,\text{cm}$ box."

Maximum size: must fit in a $10\,\text{cm} \times 10\,\text{cm} \times 10\,\text{cm}$ volume. Size limits restrict the physical dimensions allowed.
Identify the correct criterion statement format: measurable "achieve" goal or vague preference?

A measurable "achieve" goal. Criteria define specific, quantifiable performance targets.
Which option is a realistic constraint category for classroom thermal-device design: budget or "must be perfect"?

Budget. Cost limits are practical constraints in real design projects.
Which term describes a limitation such as "mass must be less than $2\ \text{kg}$ "?

Constraint. Limitations restrict what can be done in the design.
What safety-related constraint commonly applies to devices that control thermal energy transfer?

Must not cause burns, fires, or release toxic materials. Safety requirements limit materials and operating conditions.
What is one valid criterion for a container designed to keep a drink cold for 2 hours?

Keep liquid temperature above $0\,^{\circ}\text{C}$ and below $10\,^{\circ}\text{C}$ for 2 h. Specifies measurable temperature range and time duration.
What is the formula for thermal energy transfer using specific heat: $Q$ in terms of $m$ , $c$ , and $\Delta T$ ?

$Q = mc\Delta T$ . Heat energy equals mass times specific heat times temperature change.
Which term names a measurable target like "reduce heat loss by 50%": criterion or constraint?

Criterion. Criteria are goals to meet; constraints are limits to work within.
Which surface property best reduces radiative heat transfer: high emissivity or low emissivity?

Low emissivity. Low emissivity surfaces reflect rather than emit radiation.
What material property is most important for a device designed to reduce conduction through a wall?

Low thermal conductivity (good insulator). Insulators resist heat flow through direct contact between materials.
What is conduction in thermal energy transfer?

Transfer by direct contact between particles in materials. Heat flows through solids when particles vibrate and collide.
What is a common real-world constraint related to resources when designing a thermal control device?

Maximum cost (budget limit) for materials and construction. Budget limits restrict material and design choices.
Which term names a limit like "must cost under $10": criterion or constraint?

Constraint. Constraints impose restrictions on the design process.
Identify the correct constraint statement format: "must" statement or "should" statement?

A constraint is written as a "must" statement. Constraints use mandatory language like "must" or "shall".
Which term names a limit such as "must fit in a $1\,\text{L}$ container" or "budget under $10"?

Design constraint. Constraints set boundaries on resources or specifications.
What material category is typically chosen to increase conduction in a thermal-control device?

Conductors. Metals and other materials with high thermal conductivity transfer heat quickly.
Which design choice best increases convection for cooling: adding vents or sealing the device?

Adding vents. Openings allow air flow to carry heat away.
Which option is a constraint rather than a criterion: "use only recycled materials" or "reduce heat loss"?

Use only recycled materials. Material restrictions limit design choices, not performance goals.
What is the correct unit for temperature difference in a thermal-control performance criterion?

Degrees Celsius ($^ $) or kelvin ($ K$). Standard SI units for measuring temperature changes.
Which term describes a measurable goal such as "keep contents between $0\,^{\circ}\text{C}$ and $5\,^{\circ}\text{C}$ "?

Criterion. Goals to achieve are criteria, not limitations.
Which design feature is a direct way to reduce convection inside a container holding warm air?

A tight lid or seal that reduces air movement. Preventing air circulation stops heat transport by moving fluids.
Which material property should be low to reduce conduction through a device: thermal conductivity $k$ or density $\rho$ ?

Thermal conductivity $k$ . Lower $k$ means less heat flows through the material.
Which surface property best reduces radiative heat transfer: high emissivity or low emissivity?

Low emissivity. Low emissivity surfaces reflect rather than emit radiation.
Which thermal transfer mechanism is transfer by electromagnetic waves and needs no matter?

Radiation. Heat travels as infrared waves through empty space.
Which term refers to how well a thermal-control device reduces heat transfer: criterion or constraint?

Criterion. Performance goals are criteria; limitations are constraints.
Which option is a constraint: "keep contents near $20\,^{\circ}\mathrm{C}$ " or "must be built in 2 days"?

Must be built in 2 days. Time limits restrict the design process.
What is the definition of a design constraint for a device that controls thermal energy transfer?

A limit or restriction on the design (resources, size, cost, safety). Constraints set boundaries the design cannot exceed.
What is a constraint in engineering design for a device that controls thermal energy transfer?

A limit the design must follow, such as cost, size, time, or materials. Constraints are boundaries that restrict design choices.
Which term names a limit such as "must fit in a $1\,\text{L}$ box": criterion or constraint?

Constraint. Size limits restrict design options, making them constraints.
Which constraint category best matches "must fit in a backpack pocket" for a thermal device?

Size/volume constraint. Physical dimensions limit where the device can be used.
What is the meaning of a design criterion when building a device that controls heat transfer?

A required performance goal the device must achieve. Criteria define what the device must accomplish to be successful.
Which mechanism is mainly targeted by adding a foam layer between a hot object and the outside air?

Conduction. Foam blocks direct heat flow through solid contact.
What is the meaning of a design constraint when building a device to control heat transfer?

A limit on the design, such as cost, size, or materials. Constraints restrict design choices and resources.
What surface property should be maximized to reduce heat transfer by radiation?

High reflectivity (shiny, low-emissivity surface). Shiny surfaces reflect infrared waves instead of absorbing them.
Which requirement is most directly about controlling convection: "seal the lid" or "use a metal shell"?

Seal the lid. Sealing prevents air circulation that transfers heat.
What is one common environmental constraint that can affect thermal-control device design?

Operating temperature range of the surroundings. Devices must function within expected environmental conditions.
Which term names the measurable standard used to judge success: criterion or constraint?

Criterion. Criteria are goals to meet; constraints are limits to work within.
Which term refers to the measurable goal: "Keep contents between $2\,^{\circ}\text{C}$ and $8\,^{\circ}\text{C}$ "?

Criterion. Goals are criteria; this sets a specific performance target.
What is convection in thermal energy transfer?

Transfer by movement of a fluid (liquid or gas). Heated fluids rise and cooler fluids sink, creating currents.
What is convection in the context of heat transfer between a surface and a fluid (air or water)?

Thermal energy transfer by moving fluid that carries energy. Fluids transport heat as they circulate due to density differences.
Which term means a goal used to judge success: criterion or constraint?

Criterion. Criteria are benchmarks for evaluating design effectiveness.
What material category is typically chosen to reduce conduction in a thermal-control device?

Insulators. Materials like foam or fiberglass have low thermal conductivity.
Which term names a measurable goal such as "keep contents above $50\,^{\circ}\text{C}$ for 2 h": criterion or constraint?

Criterion. Criteria are measurable targets; constraints are restrictions.
What is radiation in the context of thermal energy transfer to or from a device?

Heat transfer by electromagnetic waves (infrared). All objects emit infrared radiation based on temperature.
What is a measurable criterion statement for temperature control using a target range?

Keep temperature between $T_{min}$ and $T_{max}$ . Specifies exact performance limits with measurable values.
Identify whether this statement is a criterion or constraint: "The device must weigh less than $0.5\ \text{kg}$ ."

Constraint. Mass limits are restrictions, not goals.
Which design choice increases conductive heat transfer most directly: copper plate or foam pad?

Copper plate. Copper has high thermal conductivity.
What is the primary purpose of insulation in a thermal-control device?

To slow thermal energy transfer between regions. Insulation creates resistance to heat flow.
What is a common size constraint that can affect thermal energy transfer device design?

Maximum dimensions (must fit within a specified length, width, and height). Device must physically fit in the allowed space.
What is radiation in the context of heat transfer between objects without contact?

Thermal energy transfer by electromagnetic waves (infrared). All objects emit infrared waves that carry thermal energy.
What is the formula for thermal energy transferred when temperature changes, using specific heat?

$Q = mc\Delta T$ . Relates heat ( $Q$ ), mass ( $m$ ), specific heat ( $c$ ), and temperature change ( $\Delta T$ ).
Which option is a criterion: "cost less than $5" or "keep the inside temperature stable"?

Keep the inside temperature stable. Temperature stability is a performance goal, not a limitation.
What is a clear, measurable criterion for an insulating container intended to slow cooling?

Maintain target temperature for a specified time interval. Provides measurable success metric for insulation performance.
Which design feature is a clear criterion for reducing convection in a container?

Seal or minimize air movement (airtight lid, small gaps). Stopping fluid movement prevents heat transport by convection currents.
Identify the best safety constraint for a hand-held hot pack: limit internal temperature or maximize mass?

Limit internal temperature. Prevents burns by capping maximum temperature.
Which term means a measurable standard used to judge success: criterion or constraint?

Criterion. Criteria are goals to meet; constraints are limits to respect.
What is the meaning of a design criterion when building a device that controls heat transfer?

A required feature or performance goal the device must achieve. Criteria define what the device must accomplish to be successful.
What is a clear, measurable criterion for a device intended to remove heat from an object?

Reduce temperature to a target value within a set time. Cooling devices need measurable temperature reduction goals.
Which term describes a limit like "must fit in a $10\,\mathrm{cm}$ cube": criterion or constraint?

Constraint. Size limits restrict design options, making them constraints.
What is the primary criterion for a thermal-control device intended to cool an object quickly?

Maximize heat transfer out of the object. Rapid cooling requires efficient heat removal pathways.
Which option is the better criterion statement: "use cardboard" or "limit temperature drop to $\le 5\,^{\circ}\text{C}$ in 10 min"?

Limit temperature drop to $\le 5\,^{\circ}\text{C}$ in 10 min. Criteria must be measurable performance goals.
Which requirement is most directly about controlling radiation: "use a reflective foil" or "add a thick handle"?

Use a reflective foil. Foil reflects electromagnetic waves that carry heat.
Which material type should be chosen to reduce conductive heat transfer: conductor or insulator?

Insulator. Insulators have low thermal conductivity, blocking heat flow.
Which constraint category best matches "must cost less than $15 to build"?

Cost constraint. Budget limits restrict material and design choices.
Which design choice reduces radiative heat transfer most directly: shiny foil layer or matte black paint?

Shiny foil layer. Shiny surfaces reflect electromagnetic waves.
Which design feature most directly reduces convection in a container that must stay warm?

Reducing air movement (sealed or trapped air layer). Still air is a poor heat conductor, preventing convection currents.
What design feature most directly reduces convection between a warm object and air?

A barrier that traps air or blocks fluid motion (sealed/insulated layer). Stopping air movement prevents heat transfer by convection currents.
Identify the constraint type for "Total cost must be under $15" in a thermal-control device design.

Cost constraint. Sets a budget limit for the project.
Identify the constraint: "Keep the device under $10 total cost."

Cost limit ($10 maximum). Budget restrictions limit material and design choices.
Which design choice most directly reduces convection: adding a lid, painting black, or using metal walls?

Adding a lid. Lids prevent warm air from rising and escaping the container.
Which mechanism is mainly targeted by adding a shiny foil layer facing outward on a thermal-control device?

Radiation. Reflective surfaces reduce infrared emission and absorption.
What is the definition of a design criterion for a device that controls thermal energy transfer?

A required feature or performance goal the device must achieve. Criteria define what the device must accomplish to be successful.
What are the three main mechanisms of thermal energy transfer a device may control?

Conduction, convection, and radiation. These are the three ways heat moves between objects.
Identify the criterion in this statement: "Keep a drink above $50^ $ for $30$ minutes."

Keep a drink above $50^ $. This is the performance goal the device must meet.
Which design change most directly reduces conduction: thicker insulation or adding ventilation holes?

Thicker insulation. More material creates greater resistance to heat flow.
Identify whether "must reduce heat transfer by at least $50\%$ " is a criterion or a constraint.

Criterion. Performance goals define success, making this a criterion.
What is the meaning of a design constraint when building a device that controls heat transfer?

A limit on the design, such as cost, size, or materials. Constraints restrict design choices and set boundaries.
Identify the independent variable when testing insulation thickness on heat loss.

Insulation thickness. The variable you change to test its effect on heat loss.
What is convection in the context of thermal energy transfer that a device may reduce or increase?

Thermal energy transfer by motion of a fluid (liquid or gas). Moving fluids carry thermal energy with them.
Which statement is a criterion, not a constraint: "Cost must be under $10" or "Reduce heat transfer"?

Reduce heat transfer. States a performance goal, not a limitation.
What are the three main mechanisms of thermal energy transfer a device may control?

Conduction, convection, and radiation. Heat moves through direct contact, fluid motion, and electromagnetic waves.
What is the meaning of a design criterion when building a device to control heat transfer?

A desired performance goal the device should achieve. Criteria specify what the device must accomplish, not how.
Which change reduces conduction in $\dot{Q}=\frac{kA\Delta T}{L}$ : increase $L$ or increase $k$ ?

Increase $L$ . Thicker materials ( $L$ ) provide more resistance to heat flow.
Identify whether this statement is a criterion or constraint: "The device must fit in a $20\ \text{cm}$ backpack."

Constraint. Size limits are restrictions the design must work within.
Which material type best reduces conduction in a thermal-control device: conductor or insulator?

Insulator. Insulators have low thermal conductivity, blocking heat flow.
Which option is a constraint rather than a criterion: "mass less than $0.5\,kg$ " or "reduce heat loss"?

Mass less than $0.5\,kg$ . Mass limit restricts design; heat loss reduction is a goal.
Which material property is most directly used as a criterion for reducing conduction through a device?

Low thermal conductivity (good insulation). Materials with low conductivity slow heat flow through solids.
What material property is most directly used to reduce heat transfer by conduction?

Low thermal conductivity (good insulation). Materials with low $k$ values resist heat flow through direct contact.
What is conduction in the context of thermal energy transfer through a device wall?

Heat transfer by direct contact through a material. Molecules vibrate and pass energy through solid materials.
What surface property should be specified to increase heat transfer by radiation?

High emissivity (dark, matte surface). Dark surfaces absorb and emit radiation more efficiently.
What is the meaning of a design constraint when building a device that controls thermal energy transfer?

A limit on the design, such as cost, size, time, or materials. Constraints are boundaries that restrict possible solutions.
Identify the constraint type for "Use only recycled materials" in a thermal-control device design.

Materials constraint. Limits the types of materials allowed in construction.
What is the definition of conduction as a mode of thermal energy transfer?

Thermal energy transfer by direct contact of particles. Particles vibrate and transfer energy to neighboring particles.
What design choice most directly reduces conductive heat transfer through a wall?

Use a low-conductivity material and increase thickness. Poor conductors and thicker barriers resist heat flow better.
Which design choice best reduces convection in a container: sealed air space or open vents?

Sealed air space. Trapped air prevents fluid movement and heat transfer.
What does the variable $\Delta T$ represent in the criterion equation $Q = mc\Delta T$ ?

The temperature change, $\Delta T = T_f - T_i$ . Final minus initial temperature gives the change.
What design approach most directly reduces heat transfer by convection?

Prevent fluid motion (seal gaps or trap air). Convection requires moving fluids to carry heat.
What is the key criterion difference between an insulator and a conductor in thermal-control design?

Insulator slows heat transfer; conductor speeds heat transfer. This describes their opposite effects on heat flow rate.
What is the meaning of a design constraint when building a device to control thermal energy transfer?

A limit on materials, cost, size, time, or safety. Constraints restrict design choices due to practical limitations.
What material property is most important for reducing conduction through a device wall?

Low thermal conductivity (good insulation). Poor conductors slow heat flow through solid materials.
What is a clear performance metric for thermal control that uses a temperature change symbol?

$\Delta T$ (temperature change) over a stated time interval. Quantifies thermal performance with measurable units.
Which requirement is most directly about controlling conduction: "use foam" or "use a reflective foil"?

Use foam. Foam is an insulator that reduces heat flow through solids.
Which option best defines a constraint about available resources: "minimize heat loss" or "build in $45$ minutes"?

Build in $45$ minutes. Time limits are resource constraints, not performance goals.
Which mode of heat transfer is most directly reduced by adding thick foam insulation to walls?

Conduction. Foam's low conductivity blocks particle-to-particle heat transfer.
What is convection (in the context of thermal energy transfer devices)?

Thermal energy transfer by movement of a fluid (liquid or gas). Moving fluids carry thermal energy from one place to another.
What is the meaning of a design constraint when building a device that controls thermal energy transfer?

A limit on the design, such as cost, size, time, or materials. Constraints are restrictions that limit design choices.
Identify the criterion: "The device must keep water above $50\,^{\circ}\mathrm{C}$ for $30$ minutes."

Maintain $T > 50\,^{\circ}\mathrm{C}$ for $30$ minutes. Performance goal specifies temperature and time requirements.
What is one valid constraint related to materials for a thermal-control device used by students?

Must use non-toxic, non-flammable materials. Safety constraints protect users from harmful substances.
What is conduction in the context of heat transfer through a device wall or solid material?

Thermal energy transfer by direct contact through particles in a material. Heat flows through solids when particles vibrate and collide.
What is conduction in the context of controlling thermal energy transfer in a device?

Thermal energy transfer through direct contact of particles. Heat flows when particles collide and transfer kinetic energy.
Which term means "maximum cost allowed": criterion or constraint?

Constraint. Cost limits are restrictions, making them constraints.
What is the meaning of a design criterion when building a device that controls thermal energy transfer?

A required feature or goal the device must achieve. Criteria define what the device must accomplish to be successful.
Choose the heat-transfer mode mainly reduced by adding a shiny foil layer facing an air gap in a device wall.

Radiation. Reflective surfaces reduce infrared emission and absorption.
Identify the criterion in this requirement: "The device must reduce heat loss so the temperature drops by at most $5\,^{\circ}\text{C}$ in 20 min."

Performance: temperature drop must be $\le 5\,^{\circ}\text{C}$ in 20 min. This specifies how well the device must perform its function.
Which constraint category best matches "must be made only from cardboard, foil, and tape"?

Materials constraint. Available materials restrict construction options.
What is the meaning of a design criterion when building a device that controls thermal energy transfer?

A desired feature or performance goal the device should achieve. Criteria define what the device must accomplish successfully.
Identify the criterion in this statement: "The device must keep ice from melting for $2$ hours."

Keep ice from melting for $2$ hours. This states a measurable performance goal the device must achieve.
What is conduction in the context of thermal energy transfer through a device or material?

Thermal energy transfer by direct contact between particles. Heat flows through materials when particles collide.
What is the meaning of a design criterion when building a device that controls thermal energy transfer?

A required feature or performance goal the device must achieve. Criteria define what the device must accomplish to be successful.
What is a criterion in engineering design for a device that controls thermal energy transfer?

A desired feature or performance goal the device should achieve. Criteria define what the device should accomplish to be successful.
Which option is a constraint: "use only recycled materials" or "minimize heat transfer by radiation"?

Use only recycled materials. Material restrictions limit design choices, not performance goals.
Which design choice most directly reduces convection in a container: sealing air gaps or adding metal fins?

Sealing air gaps. Prevents fluid movement that carries heat away.
What is the definition of a design criterion for a device that controls thermal energy transfer?

A required feature or performance goal the device must achieve. Criteria specify what the device should accomplish or how well it performs.
Which material type is typically chosen to reduce conduction: conductor or insulator?

Insulator. Insulators have low thermal conductivity, blocking heat flow.
What surface property should be specified to reduce heat transfer by radiation?

Low emissivity (shiny, reflective surface). Reflective surfaces emit less thermal radiation than dark ones.
Which option is the better constraint statement: "must be safe" or "no exposed surface above $60\,^{\circ}\text{C}$ "?

No exposed surface above $60\,^{\circ}\text{C}$ . Quantified safety limits are clearer than vague statements.
What is a common safety constraint to include when designing a device that controls thermal energy transfer?

Surface temperature stays below a safe limit to prevent burns. Prevents injury by limiting maximum surface temperature.
Which option is a safety constraint for a thermal device: "surface under $45\,^{\circ}\text{C}$ " or "use foam"?

"Surface under $45\,^{\circ}\text{C}$ ". Temperature limits prevent burns and ensure user safety.
What design feature most directly reduces convection in a container holding a hot liquid?

A tight lid or sealed air space to limit fluid motion. Convection requires fluid movement to carry heat away.
Which option best represents a measurable criterion: "lightweight" or "mass is less than $1\ \text{kg}$ "?

Mass is less than $1\ \text{kg}$ . Specific values make criteria testable and objective.
Identify whether "The device must keep $\Delta T \le 5\,^{\circ}\text{C}$ in 30 minutes" is criterion or constraint.

Criterion. This sets a performance goal, not a design limitation.
What is the meaning of a design criterion for a device that controls thermal energy transfer?

A required feature or performance goal the device must achieve. Criteria define what the device should accomplish, not how.
Which option is a measurable criterion for a thermal-control device: "comfortable" or "temperature stays between $20^ $ and $25^ $"?

Temperature stays between $20^ $ and $25^ $. Specific numbers make criteria measurable and testable.
What property describes how well a material resists heat flow in a thermal-control device?

Thermal insulation (low thermal conductivity). Materials with low thermal conductivity slow heat transfer.
What design feature most directly reduces heat transfer by convection around an object?

Trapping still air or sealing to prevent fluid circulation. Still air can't carry heat away by fluid motion.
Which material property is a key criterion when choosing an insulator to reduce conduction?

Low thermal conductivity. Insulators resist heat flow, having poor thermal conductivity.
What is radiation in the context of thermal energy transfer that a device may block or reflect?

Thermal energy transfer by electromagnetic waves. Heat travels as waves without needing matter.
Which surface property best reduces heat transfer by radiation: shiny/reflective or dull/dark?

Shiny or reflective. Reflective surfaces bounce electromagnetic waves away.
Which term refers to a maximum allowed budget for a thermal-control device: criterion or constraint?

Constraint. Budget limits what you can spend, making it a design restriction.
Which variable in $Q = mc\Delta T$ is most directly controlled by insulation performance: $m$ , $c$ , or $\Delta T$ ?

$\Delta T$ . Insulation reduces temperature change by slowing heat transfer.
What is one valid constraint related to size for a handheld thermal-control device?

Must fit within specified dimensions (maximum length, width, and height). Size constraints ensure the device meets practical use requirements.
Which variable is most appropriate to measure as a criterion for an insulating device: temperature change or color?

Temperature change. Temperature directly measures thermal control effectiveness.
Which thermal transfer mechanism is direct transfer through particle collisions in a solid?

Conduction. Heat flows when particles bump into neighbors.
Which choice better addresses radiation control: "paint it black" or "add a reflective foil layer"?

Add a reflective foil layer. Reflective surfaces minimize radiation absorption and emission.
What are the three main mechanisms of thermal energy transfer to consider in a device design?

Conduction, convection, and radiation. These are the fundamental ways heat moves between objects.
What is convection in the context of controlling thermal energy transfer in a device?

Thermal energy transfer by movement of a fluid (liquid or gas). Moving fluids carry thermal energy from place to place.
Which term means a limitation that the design must not violate: criterion or constraint?

Constraint. Constraints restrict what you can do in the design.
Choose the best material for a criterion "maximize heat transfer to a pan": wood, plastic, or aluminum.

Aluminum. Metals have high thermal conductivity for efficient heat transfer.
Which option is a size constraint: "fits in $20\,\text{cm}\times20\,\text{cm}\times20\,\text{cm}$ " or "reduce radiation"?

"Fits in $20\,\text{cm}\times20\,\text{cm}\times20\,\text{cm}$ ". Physical dimensions are fixed limits the design cannot exceed.
Which option best represents a constraint: "keep contents warm" or "cost is less than $15"?

Cost is less than $15. Cost limits are restrictions, not performance goals.
Which surface property is a criterion for reducing radiative heat transfer: shiny or dull?

Shiny (reflective). Reflective surfaces bounce infrared radiation away.
Choose the best constraint statement: "Be easy" or "Be buildable using only classroom materials"?

Be buildable using only classroom materials. Specific material limits are clear constraints versus vague terms.
Which mode of heat transfer is most directly reduced by using a shiny foil layer facing a hot source?

Radiation. Shiny surfaces reflect infrared waves rather than absorbing them.
Which term names the limiting factor that restricts design choices: criterion or constraint?

Constraint. Constraints impose boundaries on what designers can do.
Which option is the better constraint statement: "keep warm for 30 min" or "mass must be $\le 0.50\,\text{kg}$ "?

Mass must be $\le 0.50\,\text{kg}$ . Constraints limit design choices, not performance goals.
Identify whether this statement is a criterion or constraint: "The device must reduce heat loss."

Criterion. Performance goals are criteria, not limitations.
Which statement is the best single criterion for an insulating device: "minimize $\Delta T$ over time" or "use foam"?

Minimize $\Delta T$ over time. States a measurable goal; "use foam" is a constraint.
What is the definition of a design constraint for a device that controls thermal energy transfer?

A limit or restriction the design must obey. Constraints are boundaries that cannot be exceeded in the design.
Identify whether "Cost must be under $15" is a criterion or a constraint.

Constraint. Budget limits are resource restrictions, not performance targets.
What is the correct unit for time in a constraint such as "maintain temperature for 30 minutes"?

Seconds ( $s$ ) or minutes ( $min$ ). Standard units for measuring duration.
What is the meaning of a design constraint when building a thermal-control device?

A limit on the design, such as cost, size, or materials. Constraints restrict design choices and set boundaries.
Which surface property is a criterion if the goal is to reduce heat transfer by radiation?

Low emissivity (shiny, reflective surface). Reflective surfaces emit less thermal radiation than dark surfaces.
What is the definition of convection as a mode of thermal energy transfer?

Thermal energy transfer by motion of a fluid (liquid or gas). Moving fluids carry thermal energy from one place to another.
Identify the constraint type for "Mass must be less than $0.50\,\mathrm{kg}$ " in a thermal-control device design.

Mass (weight) constraint. Restricts how heavy the device can be.
What is convection in the context of thermal energy transfer around a device?

Heat transfer by moving fluids (liquids or gases). Moving fluids carry thermal energy with them.
Which option is the best measurable criterion: "works well" or "keeps water above $40\,^{\circ}\text{C}$ for 1 hour"?

Keeps water above $40\,^{\circ}\text{C}$ for 1 hour. Specific values and conditions make criteria testable.
Identify whether "The device must use only recycled materials" is a criterion or a constraint.

Constraint. This limits material choices, not performance targets.
Which option is a measurable criterion rather than a vague goal: "lightweight" or "mass $<0.5\,\mathrm{kg}$ "?

Mass $<0.5\,\mathrm{kg}$ . Specific numerical values make criteria testable and comparable.

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