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Apply Energy
Concepts

Master energy conservation and transformations — and learn to track energy as it changes form without ever being lost.

GED Science

What Is Energy?

Energy is the ability to do work or cause change. It is everywhere — in moving cars, glowing lights, warm coffee, and stretched rubber bands. Energy is measured in joules (J).

Two Big Categories

Kinetic Energy
The energy of motion. A rolling ball, flowing water, or moving air all have kinetic energy.
Potential Energy
Stored energy due to position or condition. A book on a shelf or a stretched spring stores potential energy.

Energy in Action

Top Max PE Bottom Max KE PE becomes KE

Law of Conservation of Energy

In any closed system, the total energy stays constant. If kinetic energy goes up, some other form (like potential energy) must go down by the same amount:

$$E_{\text{total}} = KE + PE = \text{constant}$$

The Energy Formulas

Kinetic Energy
\( KE = \tfrac{1}{2}mv^2 \)
where \( m \) = mass (kg) and \( v \) = speed (m/s).
Gravitational PE
\( PE = mgh \)
where \( g \approx 9.8\,\text{m/s}^2 \) and \( h \) = height (m).

Transformation vs. Transfer

Transformation
Energy changes form within an object. Example: chemical energy in food becomes kinetic energy when you run.
Transfer
Energy moves between objects, staying the same form. Example: a hot pan heats water by transferring thermal energy.

How to Apply Energy Concepts

1
Identify the energy forms. What energy is present at the start and end (kinetic, potential, thermal, etc.)?
2
Track the transformation. Describe how one form changes into another.
3
Apply conservation. The total energy before equals the total energy after.
4
Calculate with formulas. Use \( KE = \tfrac{1}{2}mv^2 \) and \( PE = mgh \) when numbers are given.

Example 1: Falling Object

A \( 2\,\text{kg} \) rock sits on a cliff \( 10\,\text{m} \) high. What is its gravitational potential energy?

Example 2: Moving Car

A \( 1000\,\text{kg} \) car travels at \( 20\,\text{m/s} \). Find its kinetic energy.

Example 3: Energy Chain

Chemical (battery) Electrical (current) Light (bulb)

Common Mistakes

✕ "Energy is used up"
Energy is never destroyed. It transforms into other forms, often into heat.
✕ Forgetting to square v
In \( KE = \tfrac{1}{2}mv^2 \), the speed must be squared before multiplying.
✕ Mixing up KE and PE
Motion means kinetic; height or stored condition means potential.

Quick Summary

Kinetic Energy Potential Energy
Depends onSpeedPosition / condition
Formula\( \tfrac{1}{2}mv^2 \)\( mgh \)
ExampleMoving carBook on a shelf
UnitJoules (J)Joules (J)

Question 1 of 5

According to the Law of Conservation of Energy, energy can be:

Question 2 of 5

A ball sits at the top of a hill. As it rolls down, its energy mainly changes from:

Question 3 of 5

A \( 3\,\text{kg} \) box rests on a shelf \( 4\,\text{m} \) high. Using \( PE = mgh \) with \( g = 9.8 \), its potential energy is:

Question 4 of 5

If a car's speed doubles, its kinetic energy (using \( KE = \tfrac{1}{2}mv^2 \)) becomes:

Question 5 of 5

In a flashlight, chemical energy in the battery is converted to electrical energy and then to light. This is an example of:

The Big Idea

1
Energy is conserved. It is never created or destroyed.
2
It changes form. Kinetic, potential, thermal, chemical, electrical, light, and more.
3
Formulas help. Use \( KE = \tfrac{1}{2}mv^2 \) and \( PE = mgh \) to put numbers to it.

You Can Apply Energy Concepts

You can now identify energy forms, track transformations, and use conservation to explain how energy moves through the world.