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United StatesPhysics

Unit 2: Force and Translational Dynamics

9 dot points across 9 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

Why does an object moving in a circle at constant speed still accelerate, and what provides the force that keeps it on its circular path?

Topic 2.9 Circular Motion: analyze uniform circular motion using centripetal acceleration and the net inward (centripetal) force that produces it.
A focused answer to AP Physics 1 Topic 2.9, covering uniform circular motion, centripetal acceleration, the centripetal force as the net inward force, period and speed relationships, and common real-world examples, with full worked examples.
10 min answer →

How do we represent all the forces acting on an object and combine them to find the single net force that determines its motion?

Topic 2.2 Forces and Free-Body Diagrams: identify the forces acting on an object, represent them on a free-body diagram, and calculate the net force as the vector sum of all forces.
A focused answer to AP Physics 1 Topic 2.2, covering contact and field forces, how to draw a correct free-body diagram, resolving forces into components, and calculating the net force as a vector sum, with full worked examples.
10 min answer →

What determines the gravitational force between two masses, and how does this relate to weight and the gravitational field near a planet?

Topic 2.6 Gravitational Force: use Newton's law of universal gravitation to find the force between masses, and relate this to weight and the gravitational field strength near a planet's surface.
A focused answer to AP Physics 1 Topic 2.6, covering Newton's law of universal gravitation, the inverse-square dependence on distance, gravitational field strength, the distinction between mass and weight, and how g arises near a planet, with full worked examples.
10 min answer →

How do static and kinetic friction differ, and how do we calculate the friction force using the normal force and the coefficient of friction?

Topic 2.7 Kinetic and Static Friction: distinguish static from kinetic friction, and calculate friction forces using the coefficient of friction and the normal force.
A focused answer to AP Physics 1 Topic 2.7, covering the difference between static and kinetic friction, the friction equations with the coefficient of friction and normal force, why static friction is a variable up to a maximum, and how friction enters Newton's second law, with full worked examples.
10 min answer →

Why does an object keep doing what it is doing unless a net force acts, and what does this tell us about inertia and equilibrium?

Topic 2.4 Newton's First Law: state Newton's first law, relate it to inertia, and apply the condition of zero net force to objects in translational equilibrium.
A focused answer to AP Physics 1 Topic 2.4, covering Newton's first law, inertia and mass, the meaning of equilibrium, and how to apply the zero-net-force condition to objects at rest or moving at constant velocity, with full worked examples.
9 min answer →

How does the net force on an object determine its acceleration, and how does mass mediate that relationship?

Topic 2.5 Newton's Second Law: relate the net force on an object to its acceleration and mass through Fnet = ma, and use it to solve for forces, masses or accelerations.
A focused answer to AP Physics 1 Topic 2.5, covering Newton's second law, the proportionality of acceleration to net force and inverse proportionality to mass, applying it axis by axis, and solving multi-force problems, with full worked examples.
10 min answer →

Why does every force come in a pair, and why do these paired forces not cancel each other out?

Topic 2.3 Newton's Third Law: state Newton's third law, identify action-reaction force pairs, and explain why the paired forces act on different objects and so do not cancel.
A focused answer to AP Physics 1 Topic 2.3, covering Newton's third law, how to identify action-reaction pairs, why paired forces act on different objects and never cancel, and how this connects to tension and contact forces, with full worked examples.
9 min answer →

How does the force from a stretched or compressed spring depend on how far it is displaced, and what does Hooke's law tell us?

Topic 2.8 Spring Forces: apply Hooke's law to relate the force from an ideal spring to its displacement, and use it in equilibrium and dynamics problems.
A focused answer to AP Physics 1 Topic 2.8, covering Hooke's law, the meaning of the spring constant, the restoring nature of the spring force, and how to use spring forces in equilibrium and Newton's second law problems, with full worked examples.
9 min answer →

What is a system, and how does treating an object or group of objects as a single point at its center of mass simplify the analysis of motion?

Topic 2.1 Systems and Center of Mass: define a system and its center of mass, and explain how the center of mass of a system moves in response to external forces.
A focused answer to AP Physics 1 Topic 2.1, covering what a system is, internal versus external forces, the center of mass and how to locate it, and how the center of mass responds only to external forces, with full worked examples.
9 min answer →