1. Ch.6.3 Elastic and Inelastic Collisions

2. Bell Ringer
A 40 kg miniature horse runs west at 8m/s. What is the force of impact if it hits a wall and comes to a stop in 0.5s?

3. Objectives
We will demonstrate and apply the laws of conservation of momentum in one dimension.
I will complete a worksheet, notetaking & drawing to demonstrate & apply conservation of momentum in elastic & inelastic collisions
(6D)

4. AGENDA conservation of momentum
Intro to types of collisions&Examples inelastic vs elastic collisions
Complete worksheet
Reminder:
Egg drop- next Tuesday1/17
Missed Friday assignment- Thursday is last day!

5. Conservation of Momentum
Principle that states that the total momentum of an isolated system stays constant.
Total momentum before a collision equals total momentum after a collision
p = 30 kg·m/s
p = 20 kg·m/s
p = 20 kg·m/s
p = 30 kg·m/s
Total = 50 kg·m/s
Total = 50 kg·m/s

6. Conservation of Momentum Equation
𝑝 (𝑡𝑜𝑡𝑎𝑙) = 𝑝′ (𝑡𝑜𝑡𝑎𝑙)
m1v1+m2v2= m1v1’ +m2 v2’
p (total)  sum of momentum BEFORE
p’ (total)  sum of momenta AFTER

7. Demo: Newton’s Cradle

8. Newton’s Cradle

9. Demo: Basketball and Tennis Ball

10. Conservation of Momentum in Two Dimensions

11. Conservation of Momentum in Two Dimensions
Before
After

12. Examples
𝑝 (𝑡𝑜𝑡𝑎𝑙) = 𝑝′ (𝑡𝑜𝑡𝑎𝑙)
m1v1+m2v2= m1v1’ +m2 v2’

13. Collisions How would you define “collision?”
Is a tennis racket hitting a ball a collision?
Is a baseball glove catching a baseball a collision?
What’s different about these two situations?

14. Collisions Collisions happen whenever two objects impact each other
[NBC Learn Video-NHL]
Collisions happen whenever two objects impact each other
Sometimes the objects bounce off of each other
Sometimes the objects stick together

15. Types of Collisions
Elastic
Inelastic
Perfectly
inelastic

16. Elastic vs Inelastic Collisions
Perfectly Inelastic

17. Perfectly Inelastic Collisions
In a perfectly inelastic collision, two objects collide and stick to each other with some deformation
deformation
m1v1 + m2v2 = (m1 + m2)v’
Kinetic energy is NOT conserved because deformation takes away energy (sound, friction, etc.)
Momentum is conserved: pi = pf

18. Examples of Perfectly Inelastic Collisions

19. Elastic Collisions m1v1 + m2v2 = m1v’1 + m2v’2
In an elastic collision, two objects collide and bounce off of each other
m1v1 + m2v2 = m1v’1 + m2v’2
Kinetic energy is conserved because motion continues uninterrupted: KEi = KEf
Momentum is conserved: pi = pf

20. Real World Examples

21. Typical Elastic Collisions

22. Realistic Collisions
some deformation
Most collisions are somewhere between elastic and perfectly inelastic
For our class, we will be assuming collisions are either elastic or perfectly inelastic

23. Real World Examples

24. Problem Set Rd the problem.
Sketch a before & after pic to determine whether it is an elastic or inelastic collision
Choose the appropriate formula
Identify variables: m1, v1, m2,v2, v’1 etc.
Solve