Newton’s Third Law

Front

System Noun

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[sis-tuhm]

Back

System

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A collection of objects that can be treated as a single entity for the purpose of analyzing forces and motion.

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Example: This diagram shows two connected masses as a single 'system,' where internal and external forces (gravity, tension) determine the overall motion.

Front

Force Noun

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[fors]

Back

Force

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A push or a pull that acts on an object, possessing both a magnitude and a specific direction.

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Example: When a person pushes on a wall (action force), the wall pushes back on the person with an equal and opposite force (reaction force).

Front

Net Force Noun

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[net fors]

Back

Net Force

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The vector sum of all individual forces acting on a single object, which determines the object's acceleration.

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Example: Two teams pull a rope with equal force (300 N) in opposite directions. The forces are balanced, so the net force is zero.

Front

Inertia Noun

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[in-ur-shuh]

Back

Inertia

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The natural tendency of an object to resist any change in its state of motion, whether at rest or moving.

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Example: An object at rest, like a shopping cart, has inertia and will remain at rest until an external force is applied to make it move.

Front

Equilibrium Noun

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[ee-kwuh-lib-ree-uhm]

Back

Equilibrium

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The state of an object in which the net force acting upon it is zero, resulting in no acceleration.

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Example: Two people pull a rope with equal and opposite forces, so the rope does not move. This state of balanced forces is called equilibrium.

Front

Interaction Pair Noun

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[in-ter-ak-shuhn pair]

Back

Interaction Pair

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A set of two forces that are equal in magnitude and opposite in direction, acting on two different interacting objects.

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Example: The force of the left magnet pushing the right magnet away is an interaction pair with the equal and opposite force of the right magnet pushing the left one.

Front

Free-Body Diagram Noun

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[free-bod-ee dahy-uh-gram]

Back

Free-Body Diagram

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A simplified diagram that represents a single object and all the external forces that are acting upon it.

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Example: A free-body diagram simplifies an object to a single point and uses arrows (vectors) to show all the forces, like weight and normal force, acting on it.

Front

Weight Noun

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[weyt]

Back

Weight

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The gravitational force exerted on an object's mass by a large body, such as a planet or star.

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Example: This diagram shows that the force of gravity (weight) is a mutual attraction; the Earth pulls on an object, and the object pulls back on the Earth with an equal force.

Front

Gravitational Field Noun

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[grav-i-tey-shuhn-l feeld]

Back

Gravitational Field

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A vector field describing the gravitational force that would be applied on a test mass at any given point.

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Example: This diagram shows that two objects with mass (m1 and m2), like the Sun and Earth, exert an equal and opposite gravitational force (F1 and F2) on each other.

Front

Apparent Weight Noun

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[uh-par-uhnt weyt]

Back

Apparent Weight

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The force an object exerts on its support, which can differ from its actual weight due to acceleration.

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Example: This diagram shows how your apparent weight changes in an elevator. The upward arrow (normal force) is your apparent weight, which increases when accelerating up and becomes zero in freefall.