Why Orbits Happen - Middle School Earth and Space Science
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What is centripetal force in an orbiting system?
What is centripetal force in an orbiting system?
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The inward net force that keeps an object moving in a circle. Any force causing circular motion points toward the center.
The inward net force that keeps an object moving in a circle. Any force causing circular motion points toward the center.
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Which model describes an orbit as continuous free-fall toward a planet while moving forward?
Which model describes an orbit as continuous free-fall toward a planet while moving forward?
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The projectile (Newton’s cannon) free-fall model. Newton showed orbits are objects falling while moving forward fast.
The projectile (Newton’s cannon) free-fall model. Newton showed orbits are objects falling while moving forward fast.
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What two motions must be balanced for a stable orbit: inward pull and forward motion?
What two motions must be balanced for a stable orbit: inward pull and forward motion?
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Gravity inward and tangential (sideways) velocity forward. Orbit occurs when gravity pulls inward while object moves sideways.
Gravity inward and tangential (sideways) velocity forward. Orbit occurs when gravity pulls inward while object moves sideways.
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Which option correctly explains why astronauts feel weightless while orbiting Earth?
Which option correctly explains why astronauts feel weightless while orbiting Earth?
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They are in continuous free-fall with their spacecraft. Both astronauts and spacecraft fall together around Earth.
They are in continuous free-fall with their spacecraft. Both astronauts and spacecraft fall together around Earth.
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Identify the correct statement: If distance becomes $3r$, gravity becomes what fraction of original?
Identify the correct statement: If distance becomes $3r$, gravity becomes what fraction of original?
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It becomes $ rac{1}{9}$ of the original force. Inverse square law: tripling distance reduces force ninefold.
It becomes $ rac{1}{9}$ of the original force. Inverse square law: tripling distance reduces force ninefold.
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Which has the stronger gravitational pull: a planet on a moon or a moon on a planet?
Which has the stronger gravitational pull: a planet on a moon or a moon on a planet?
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Neither; the forces are equal in magnitude and opposite. Newton's third law: forces are action-reaction pairs.
Neither; the forces are equal in magnitude and opposite. Newton's third law: forces are action-reaction pairs.
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Identify the correct relationship for a circular orbit: gravity supplies which type of force?
Identify the correct relationship for a circular orbit: gravity supplies which type of force?
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Centripetal force. Gravity acts as the centripetal force in orbital motion.
Centripetal force. Gravity acts as the centripetal force in orbital motion.
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Which option correctly describes why orbiting objects do not “fall straight down” into the central body?
Which option correctly describes why orbiting objects do not “fall straight down” into the central body?
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They have enough tangential velocity to keep missing it. Sideways motion prevents direct collision despite constant falling.
They have enough tangential velocity to keep missing it. Sideways motion prevents direct collision despite constant falling.
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Identify the best model statement: An orbit is best described as a continuous ______ around a body.
Identify the best model statement: An orbit is best described as a continuous ______ around a body.
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free-fall. Orbiting objects are in constant free-fall but never hit the surface.
free-fall. Orbiting objects are in constant free-fall but never hit the surface.
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What is the name of the inward-directed acceleration needed to keep an object moving in a circle?
What is the name of the inward-directed acceleration needed to keep an object moving in a circle?
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Centripetal acceleration. This acceleration constantly changes direction to maintain circular motion.
Centripetal acceleration. This acceleration constantly changes direction to maintain circular motion.
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What provides the centripetal force for planets orbiting the Sun and moons orbiting planets?
What provides the centripetal force for planets orbiting the Sun and moons orbiting planets?
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Gravitational force. Gravity acts as the centripetal force that curves the path into an orbit.
Gravitational force. Gravity acts as the centripetal force that curves the path into an orbit.
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What is the velocity direction of a moon at any point in its orbit?
What is the velocity direction of a moon at any point in its orbit?
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Tangent to the orbital path at that point. Velocity is always perpendicular to the radius at any point.
Tangent to the orbital path at that point. Velocity is always perpendicular to the radius at any point.
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What model correctly describes orbiting as continuous free-fall around a planet or star?
What model correctly describes orbiting as continuous free-fall around a planet or star?
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An orbit is continuous free-fall with sideways motion. The object falls toward the center while moving sideways.
An orbit is continuous free-fall with sideways motion. The object falls toward the center while moving sideways.
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Which statement best describes why satellites do not need engines to keep orbiting?
Which statement best describes why satellites do not need engines to keep orbiting?
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They keep moving by inertia; gravity continually bends their path. No fuel needed; natural forces maintain the motion.
They keep moving by inertia; gravity continually bends their path. No fuel needed; natural forces maintain the motion.
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What two influences must balance to produce a stable orbit in the gravity-and-inertia model?
What two influences must balance to produce a stable orbit in the gravity-and-inertia model?
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Gravity inward and inertia (forward motion) outward. Gravity pulls inward while inertia maintains forward motion.
Gravity inward and inertia (forward motion) outward. Gravity pulls inward while inertia maintains forward motion.
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What is inertia in the context of an orbiting moon or planet?
What is inertia in the context of an orbiting moon or planet?
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Tendency to keep moving in a straight line at constant speed. Newton's first law: objects in motion stay in motion unless acted upon.
Tendency to keep moving in a straight line at constant speed. Newton's first law: objects in motion stay in motion unless acted upon.
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What is centripetal force in an orbital system?
What is centripetal force in an orbital system?
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The inward net force that continually bends the path into a curve. For orbits, gravity provides this center-seeking force.
The inward net force that continually bends the path into a curve. For orbits, gravity provides this center-seeking force.
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Which path best describes the motion without gravity: straight line or closed orbit?
Which path best describes the motion without gravity: straight line or closed orbit?
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Straight line. Without gravity, inertia causes motion in a straight path.
Straight line. Without gravity, inertia causes motion in a straight path.
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Which path best describes the motion with gravity only (no forward speed): fall inward or orbit?
Which path best describes the motion with gravity only (no forward speed): fall inward or orbit?
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Fall inward toward the larger body. Without forward motion, gravity pulls objects directly inward.
Fall inward toward the larger body. Without forward motion, gravity pulls objects directly inward.
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Which option correctly compares gravity at distances $r$ and $2r$ from the same planet?
Which option correctly compares gravity at distances $r$ and $2r$ from the same planet?
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At $2r$, gravity is $ rac{1}{4}$ as strong as at $r$. Inverse square law: doubling distance quarters the force.
At $2r$, gravity is $ rac{1}{4}$ as strong as at $r$. Inverse square law: doubling distance quarters the force.
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Identify the correct statement about orbital speed in an elliptical orbit.
Identify the correct statement about orbital speed in an elliptical orbit.
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It is faster when closer and slower when farther away. Conservation of angular momentum causes speed variations.
It is faster when closer and slower when farther away. Conservation of angular momentum causes speed variations.
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What is the standard classroom model that shows orbit as “falling around” a planet?
What is the standard classroom model that shows orbit as “falling around” a planet?
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A projectile model: forward motion plus downward gravity. Objects continuously fall toward but miss the planet due to forward speed.
A projectile model: forward motion plus downward gravity. Objects continuously fall toward but miss the planet due to forward speed.
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What is the shape of most natural planetary and lunar orbits?
What is the shape of most natural planetary and lunar orbits?
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Elliptical (an ellipse). Planets follow oval paths, not perfect circles.
Elliptical (an ellipse). Planets follow oval paths, not perfect circles.
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What is the name for the point in an orbit closest to the body being orbited?
What is the name for the point in an orbit closest to the body being orbited?
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Periapsis (perihelion for Sun, perigee for Earth). Prefix 'peri-' means near; suffix varies by central body.
Periapsis (perihelion for Sun, perigee for Earth). Prefix 'peri-' means near; suffix varies by central body.
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What is the name for the point in an orbit farthest from the body being orbited?
What is the name for the point in an orbit farthest from the body being orbited?
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Apoapsis (aphelion for Sun, apogee for Earth). Prefix 'apo-' means away; suffix varies by central body.
Apoapsis (aphelion for Sun, apogee for Earth). Prefix 'apo-' means away; suffix varies by central body.
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