Forces on Systems

Front

System Noun

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[sis-tuhm]

Back

System

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A collection of multiple objects chosen for analysis that interact with each other through various forces and are treated as a whole.

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Example: The Earth and Moon form a system where gravity is the force that pulls the Moon towards the Earth, keeping it in a stable orbit.

Front

Free-body diagram Noun

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

Back

Free-body diagram

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A diagram used to model and visualize all the external forces acting on a single object or a system of objects.

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Example: This diagram shows an object as a simple box, with arrows representing all the forces acting on it. Each arrow's direction and labeled size (in Newtons) show the force's direction and strength.

Front

Acceleration Noun

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[ak-sel-uh-rey-shuhn]

Back

Acceleration

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The rate of change of an object's velocity, with a system's acceleration being defined by its center of mass.

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Example: Acceleration is a change in velocity. This can mean speeding up, slowing down (negative acceleration), or changing direction, even at a constant speed.

Front

External Force Noun

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[ek-stur-nl fawrs]

Back

External Force

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A force exerted on a system by an object outside of that system, which can change the system's overall motion.

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Example: A person pushing a box is an example of an external force, a push or pull originating from outside a system and acting on it.

Front

Internal Force Noun

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[in-tur-nl fawrs]

Back

Internal Force

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A force exerted by one object within a system on another object that is also within the same system.

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Example: The arrows labeled 'B' show internal forces, like air pressure, acting within the soccer ball system to maintain its shape.

Front

Newton's Second Law Noun

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[noo-tuhns sek-uhnd law]

Back

Newton's Second Law

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The principle stating a system's acceleration is determined by the net external force divided by the system's total mass.

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Example: This diagram shows the formula for Newton's Second Law (F=ma), explaining that Force equals mass multiplied by acceleration and labeling the units for each.

Front

Newton's Third Law Noun

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[noo-tuhns thurd law]

Back

Newton's Third Law

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The principle that for every action, there is an equal and opposite reaction, explaining why internal forces cancel.

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

Front

Center of Mass Noun

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[sen-ter uhv mas]

Back

Center of Mass

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The unique point in a system whose motion is defined by the net external forces acting on the system.

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Example: This diagram shows the center of mass (C) for a system of two objects (m1 and m2), representing the system's average balance point.

Front

Tension Noun

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[ten-shuhn]

Back

Tension

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A pulling force transmitted axially through a string, rope, or cable when pulled by forces acting from opposite ends.

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Example: Two figures pull an object in opposite directions, creating a pulling force called tension that acts equally throughout the object.

Front

Apparent Weight Noun

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[uh-par-uhnt weyt]

Back

Apparent Weight

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The upward support force that opposes gravity on an object, which can change depending on the object's acceleration.

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Example: This diagram shows how apparent weight changes in an elevator. When accelerating up, you feel heavier; in freefall (accelerating down at g), you feel weightless.