Lesson 7 – Momentum & Collisions

Stage 1: Intermediate Complete Notes
Page 4 – Types of Collisions

A collision is an interaction between two or more bodies that occurs in a very short time interval, during which large impulsive forces act.

---

1️⃣ What is a Collision?

A collision occurs when two bodies come close and exert strong forces on each other for a short duration.

✔ Time of interaction is very small
✔ External forces are negligible during collision
✔ Momentum is always conserved

Collisions may occur with or without physical contact.

---

2️⃣ Classification of Collisions

Based on conservation of energy, collisions are classified as:

• Elastic collisions
• Inelastic collisions
• Perfectly inelastic collisions

---

3️⃣ Elastic Collision

In an elastic collision:

✔ Linear momentum is conserved
✔ Kinetic energy is conserved
✔ No permanent deformation occurs

Mathematical conditions:

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
½m₁u₁² + ½m₂u₂² = ½m₁v₁² + ½m₂v₂²

Example:

• Collision between gas molecules
• Ideal billiard ball collisions (approximate)

---

4️⃣ Inelastic Collision

In an inelastic collision:

✔ Momentum is conserved
❌ Kinetic energy is NOT conserved
✔ Some energy is lost as heat, sound or deformation

Example:

• Car accidents
• Clay ball hitting a wall

---

5️⃣ Perfectly Inelastic Collision

A perfectly inelastic collision is a special case of inelastic collision in which the colliding bodies stick together after collision.

✔ Bodies move together after collision
✔ Maximum loss of kinetic energy
✔ Momentum is conserved

Common example:

• Bullet embedding into a wooden block

---

6️⃣ Comparison of Collisions (Exam Focus)

Elastic collision → KE conserved
Inelastic collision → KE not conserved
Perfectly inelastic → Bodies stick together

---

7️⃣ Important Exam Points

✔ Momentum is conserved in all collisions
✔ Energy conservation distinguishes collision type
✔ Perfectly elastic collision is an ideal case

---

📌 Page 4 Summary

✔ Collision involves short interaction
✔ Momentum always conserved
✔ Elastic → KE conserved
✔ Inelastic → KE lost

👉 Next page: Coefficient of Restitution & Its Physical Meaning