← Physics C: Mechanics syllabus

United StatesPhysics C: Mechanics

Unit 2: Force and Translational Dynamics

10 dot points across 10 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

Why does uniform circular motion require a net inward force, and how do we find the centripetal acceleration and the force that supplies it?

Topic 2.10 Circular Motion: relate centripetal acceleration to speed and radius, identify the real force that supplies the centripetal force, and apply Newton's second law to circular motion including vertical circles.
A focused answer to AP Physics C: Mechanics Topic 2.10, covering centripetal acceleration as a change in the direction of velocity, the centripetal force as supplied by a real force, applying Newton's second law along the radial direction, and circular motion in horizontal and vertical circles, with worked examples.
11 min answer →

How do we represent the forces acting on an object with a free-body diagram, and how do we resolve those forces to set up the equations of motion?

Topic 2.2 Forces and Free-Body Diagrams: identify the forces acting on a chosen object, represent them on a free-body diagram, and resolve them into components on chosen axes to find the net force.
A focused answer to AP Physics C: Mechanics Topic 2.2, covering contact and field forces, drawing a correct free-body diagram showing only the forces on the chosen object, choosing convenient axes (including tilted axes on an incline), and resolving forces into components to compute the net force, with worked examples.
10 min answer →

How does Newton's law of universal gravitation describe the attraction between masses, and how does it give the gravitational field and weight near a planet?

Topic 2.6 Gravitational Force: apply Newton's law of universal gravitation, define the gravitational field strength, relate it to weight, and treat gravity inside and outside a spherical mass.
A focused answer to AP Physics C: Mechanics Topic 2.6, covering Newton's law of universal gravitation and its inverse-square character, the gravitational field strength and its relation to weight, the field outside and inside a uniform sphere, and apparent weightlessness, with calculus-aware worked examples.
11 min answer →

How do static and kinetic friction differ, and how do we use the friction models to decide whether motion starts and to find the acceleration once it does?

Topic 2.7 Kinetic and Static Friction: model kinetic friction as proportional to the normal force, treat static friction as adjustable up to a maximum, and apply both to decide whether and how an object slides.
A focused answer to AP Physics C: Mechanics Topic 2.7, covering the kinetic friction model proportional to the normal force, static friction as a self-adjusting force up to a maximum, deciding whether an object starts to slide, and applying friction on level ground and inclines, with worked examples.
10 min answer →

What does it mean for an object to be in translational equilibrium, and how do we use the condition of zero net force to solve for unknown forces?

Topic 2.4 Newton's First Law: state the law of inertia, define translational equilibrium as zero net force, and apply the equilibrium conditions to find unknown forces.
A focused answer to AP Physics C: Mechanics Topic 2.4, covering Newton's first law and inertia, the meaning of translational equilibrium as zero net force, the difference between mass and weight, and applying the equilibrium conditions axis by axis to find unknown forces, with worked examples.
10 min answer →

How does the net force on an object determine its acceleration, and how do we apply Newton's second law axis by axis and to connected systems?

Topic 2.5 Newton's Second Law: relate net force, mass and acceleration through the vector equation, apply it component by component, and extend it to connected systems and the general form with momentum.
A focused answer to AP Physics C: Mechanics Topic 2.5, covering Newton's second law as a vector equation applied axis by axis, the general form as the time rate of change of momentum, solving connected systems for the common acceleration and internal tension, and using it with variable forces, with calculus-based worked examples.
11 min answer →

Why do forces always come in equal and opposite pairs acting on different objects, and how does this constrain interactions and underpin momentum conservation?

Topic 2.3 Newton's Third Law: state that forces arise in equal-and-opposite pairs on different objects, identify the members of a third-law pair, and use this to analyze interacting systems.
A focused answer to AP Physics C: Mechanics Topic 2.3, covering Newton's third law as equal-and-opposite force pairs on different objects, identifying the members of a third-law pair, why such pairs never cancel on a single object, and how the law underlies momentum conservation, with worked examples.
10 min answer →

How do velocity-dependent resistive forces such as air resistance change motion, and how do we use calculus to find terminal velocity and the approach to it?

Topic 2.9 Resistive Forces: model a velocity-dependent resistive force, set up and solve the equation of motion for fall with drag, and determine the terminal velocity and the exponential approach to it.
A focused answer to AP Physics C: Mechanics Topic 2.9, covering velocity-dependent resistive forces (drag), setting up Newton's second law as a differential equation for an object falling through a fluid, finding the terminal velocity, and solving the linear-drag equation of motion to get the exponential approach, with calculus-based worked examples.
11 min answer →

How does an ideal spring exert a restoring force proportional to its displacement, and how does this linear force law set up oscillation and elastic energy?

Topic 2.8 Spring Forces: model the ideal spring with Hooke's law as a linear restoring force, combine springs in series and parallel, and connect the force law to elastic potential energy by integration.
A focused answer to AP Physics C: Mechanics Topic 2.8, covering the ideal spring and Hooke's law as a linear restoring force, the sign convention for the restoring direction, effective spring constants for series and parallel combinations, and the link to elastic potential energy by integrating the force, with worked examples.
10 min answer →

How do we define a system and locate its center of mass, and why does only the net external force govern the motion of the center of mass?

Topic 2.1 Systems and Center of Mass: define a system, locate the center of mass by a mass-weighted average (including by integration for continuous bodies), and apply that only external forces accelerate the center of mass.
A focused answer to AP Physics C: Mechanics Topic 2.1, covering the idea of a system, the center of mass as a mass-weighted average for discrete particles and by integration for continuous bodies, the velocity and acceleration of the center of mass, and why only external forces change the center-of-mass motion, with calculus-based worked examples.
11 min answer →