1. Chapter 7 Impulse & Momentum

2. 7.1 – The Impulse-Momentum Theorem
Why is a glass less likely to break when dropped on carpet than on a tile floor?

3. Forces may not be constant during an impact.
In these cases, we will use the average force that occurred during contact time.

4. Δt = contact time (s)

5. A larger impulse produces a larger change in velocity (Δv).
but…the Δv depends on the mass also.

6. Momentum (p) –
‘inertia in motion’
mass (kg)
velocity (m/s)

7. Impulse = change in momentum
Impulse-momentum theorem
Impulse = change in momentum
A larger impulse produces a larger change in velocity.

8. Why does ‘following-through’ on a swing increase the drive distance of a ball?

9. You’re travelling down the road and you car suddenly goes out of control but you have a choice of slamming into a haystack or a brick wall. Which would you choose?
Why?

10. Decreasing Momentum

12. When you jump off a step, you usually bend your knees as you reach the ground. By doing this, the time of the impact is about 10 times more what it would be in a stiff-legged landing and the average force on your body is reduced by _______.

14. Why is a glass less likely to break when dropped on carpet than on a tile floor?

15. ASSIGNMENT Read 7.1 Ch. 7 Problems #1,2,8
Page 206

16. 7.2 – The Principle of Conservation of Linear Momentum
The total momentum of an isolated system remains constant (is conserved).

19. System – collection of objects being considered.
Internal Forces – forces objects exert on each other within the system.
External Forces – forces exerted on the objects from outside the system.
Isolated System – The net external forces are zero.

20. ASSIGNMENT
Read 7.2 Ch. 7 Problems #17,18,19 page 207

24. 7.3 – Collisions in One Dimension
Elastic Collision – total KE does not change before/after collision.
‘bouncy’
Inelastic Collision – total KE is not the same before and after collision.
‘sticky’
Completely Inelastic Collision – objects stick together.

25. Impulse = change in momentum
Things to Know…
Impulse
Momentum
Impulse = change in momentum
Momentum is conserved unless there is a net external force.
Elastic and Inelastic Collisions

26. Try These… Ch. 7 Problems #28, 31; p. 208
31. a) v5kg = -0.4 m/s, v7.5kg = +1.6 m/s
b) +0.8 m/s

27. Coefficient of Restitution (C.O.R.)
bounce height
drop height
*For objects bouncing off floor.
*C.O.R represents the collision not the object.
*C.O.R = 1, perfectly elastic, C.O.R. = 0, inelastic

28. Impulse = change in momentum
Rain vs. Hail
Impulse = change in momentum