Elastic & Inelastic Collisions – AP Physics 1

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Elastic & Inelastic Collisions

AP Physics 1 · Unit 4: Linear Momentum

Learning Objectives

Apply conservation of momentum to collisions

Distinguish elastic (KE conserved) vs inelastic

Calculate final velocities after any 1D collision

Identify perfectly inelastic collisions (objects stick)

Key Equations

Collision Types

Elastic: Both p and KE conserved (ideal billiard balls)

Inelastic: p conserved, KE lost to heat/sound/deform

Perfectly Inelastic: Objects stick together (max KE loss)

Real-World Examples

Billiard balls (nearly elastic)

Car crashes (perfectly inelastic)

Newton's cradle (elastic)

Football tackle (inelastic)

MomentumCollisionsAP Physics 1Unit 4

Ball 1 v0.0 m/s

Ball 2 v0.0 m/s

p_total0.0 kg·m/s

⬤ BEFORE Collision

p₁ = m₁v₁-

p₂ = m₂v₂-

p_total-

KE_total-

⬤ AFTER Collision

p₁' = m₁v₁'-

p₂' = m₂v₂'-

p_total'-

KE_total'-

Momentum: —

Kinetic Energy: —

Collision Type

Elastic

Inelastic

Stick

Ball 1 (Blue)

Mass m₁ (kg) 2.0

Velocity v₁ (m/s) +6.0

Ball 2 (Orange)

Mass m₂ (kg) 2.0

Velocity v₂ (m/s) −2.0

Inelastic e (0=perfect) 1.00

Coefficient of restitution (1 = elastic)

📝 Quick Quiz▼

1. In ALL types of collisions (elastic and inelastic), which quantity is always conserved?

Kinetic energy Momentum Total mechanical energy Velocity

2. A 4 kg ball moving at 6 m/s hits a stationary 4 kg ball elastically. What are their final speeds?

Both move at 3 m/s First stops, second moves at 6 m/s First moves at 6 m/s, second stops Both stop

3. Two objects stick together after collision. The collision is:

Elastic Inelastic Perfectly inelastic Perfectly elastic