School

AP Physics

Summary: Things move but specifically in limited ways

Unit 1: Kinematics

  • Core Idea: Motion can be described, measured, and predicted using a few key quantities.
  • Position (x): Location in space
  • Displacement (Δx): Change in position
  • Velocity (v): Rate of change of position
    • v = Δx / Δt (average velocity)
  • Acceleration (a): Rate of change of velocity
    • a = Δv / Δt
  • Key Kinematic Equations (constant acceleration):
    • v = v₀ + at
    • x = x₀ + v₀t + (1/2)at²
    • v² = v₀² + 2aΔx
  • Use signs to indicate direction — negative means opposite motion or deceleration.

Unit 2: Force and Translational Dynamics

  • Core Idea: Forces cause changes in motion. Newton’s Laws explain how and why.
  • Newton’s 1st Law: An object in motion stays in motion unless acted on by a net force (inertia).
  • Newton’s 2nd Law: F = ma (net force = mass × acceleration)
  • Newton’s 3rd Law: For every action, there’s an equal and opposite reaction.
  • Free-body diagrams show all the forces acting on an object.
  • Common forces:
    • Weight: Fg = mg
    • Normal force: Perpendicular to surface
    • Friction: Opposes motion, Ff = μN
    • Tension: Force in a string/rope
    • Applied forces: Pushes or pulls

Unit 3: Work, Energy, and Power

  • Core Idea: Energy makes things move. Work transfers energy.
  • Work: W = Fd cos(θ) (force × displacement × angle between them)
  • Kinetic Energy: KE = (1/2)mv²
  • Potential Energy (gravitational): PE = mgh
  • Mechanical Energy: ME = KE + PE
  • Work-Energy Theorem: W = ΔKE
  • Power: P = W / t or P = Fv (rate of energy transfer)

Unit 4: Linear Momentum

  • Core Idea: Momentum measures motion’s “oomph.” It’s conserved in closed systems.
  • Momentum: p = mv
  • Impulse: J = FΔt = Δp
  • Conservation of Momentum:
    • In collisions, total momentum before = total after
  • Elastic collision: momentum and KE conserved
  • Inelastic collision: momentum conserved, KE not
  • Perfectly inelastic: objects stick together

Unit 5: Torque and Rotational Dynamics

  • Core Idea: Rotation works like linear motion — but with its own set of rules.
  • Torque (τ): τ = rF sin(θ) (force × lever arm × angle)
  • Moment of Inertia (I): rotational analog of mass
  • Newton’s 2nd Law for Rotation: τ = Iα (torque = moment of inertia × angular acceleration)
  • Equilibrium:
    • Translational: ∑F = 0
    • Rotational: ∑τ = 0

Unit 6: Energy and Momentum of Rotating Systems

  • Core Idea: Rotation has kinetic energy and angular momentum — just like linear systems.
  • Rotational Kinetic Energy: KE_rot = (1/2)Iω²
  • Angular Momentum: L = Iω
  • Conservation of Angular Momentum:
    • In closed systems, Li = Lf
    • Example: Ice skater pulls arms in → spins faster (I ↓, ω ↑)

Unit 7: Oscillations

  • Core Idea: Simple harmonic motion (SHM) is predictable, cyclic motion powered by restoring forces.
  • Restoring force: Always pulls toward equilibrium
    • For springs: F = -kx (Hooke’s Law)
  • Spring Potential Energy: PE_spring = (1/2)kx²
  • Simple Harmonic Motion:
    • Period (spring): T = 2π√(m/k)
    • Period (pendulum): T = 2π√(L/g)
  • SHM is a transfer between KE and PE — total energy remains constant