AP Physics 1 / Topic
Force and Translational Dynamics
Unit 2 is Newton's laws: free-body diagrams, net force, friction, inclined planes, tension systems, circular motion, and gravitation. It is the most heavily tested reasoning unit in AP Physics 1.
What the exam asks
- Draw correct free-body diagrams and identify third-law force pairs
- Apply ΣF = ma along each axis, including inclines and connected systems
- Distinguish static from kinetic friction and use the inequality for static friction
- Analyze uniform circular motion with a net centripetal force
- Use Newton's law of universal gravitation and relate g to planetary mass and radius
Key formulas and rules
ΣF = ma (apply per axis)
f(kinetic) = μk·N; f(static) ≤ μs·N
along: mg sinθ; perpendicular: mg cosθ
a = v²/r toward the center; ΣF(centripetal) = mv²/r
F = G·m1·m2 / r²; g = GM/r²
force pairs are equal magnitude, opposite direction, on different objects — always
Question bank breakdown
48
5
14 easy · 25 medium · 9 hard
Skills covered
Every question in the bank comes with a per-choice explanation, so you learn why each wrong answer is wrong — not just the key.
Sample question
From the free tier of the ScoreMint AP Physics 1 bank — try it, then check the answer.
A $5.0 \text{ kg}$ block rests on a frictionless horizontal surface. Two horizontal forces act on the block: a $20 \text{ N}$ force to the right and a $12 \text{ N}$ force to the left. What is the magnitude and direction of the block's acceleration?
- A. $1.6 \text{ m/s}^2$ to the right
- B. $6.4 \text{ m/s}^2$ to the right
- C. $1.6 \text{ m/s}^2$ to the left
- D. $4.0 \text{ m/s}^2$ to the right
Show answer and explanation
Answer: A. Newton's second law states $\vec{F}_{net} = m\vec{a}$. The net force must be computed as the vector sum of all forces acting on the object. Here, the forces are antiparallel (opposite directions along the same line), so $F_{net} = 20 - 12 = 8$ N in the direction of the larger force (right). Then $a = 8/5.0 = 1.6$ m/s$^2$ to the right. A critical skill is distinguishing between the net force and individual forces.
Study tip
Normal force is not automatically mg. Recompute N whenever the surface is inclined, the object accelerates vertically, or an applied force has a vertical component — friction answers depend on getting N right.