1. Aim: How do we explain momentum and impulse?

2. Definition of impulse-impulse momentum theorem
The total impulse of the net force ΣF on a particle equals the change in momentum of the particle. I=ʃΣFdt = Δp It also applies to a system of particles in which we consider the net force external to the system I=ʃΣFextdt = Δptot

3. Impulse approximation
I = Δp=ΣFΔt The impulse approximation: We assume that one of the forces exerted on a particle acts for a short time but is much greater than any other force present.

4. Thought Question 1
Two objects are at rest on a frictionless surface. Object 1 has a larger mass than object 2. When a force is applied to object 1, it accelerates through a displacement Δx. The force is removed from object 1 and is applied to object 2. At the moment when object 2 accelerates through the same displacement Δx, which statements are true?
p1 <p2 b) p1 = p2 c) p1>p2 d) K1 <K2
e) K1=K2 f) K1>K2

5. Thought Question 2
In boxing matches of the 19th century, bare fists were used. In modern boxing, fighters wear padded gloves. How does this better protect the brain of the boxer from injury?

6. Thought Question 3
A race car travels rapidly around a circular race track at constant speed. For a given portion of the track, what is the direction of the impulse vector. Once the car returns to the starting point, there is no net change in momentum for the entire trip around the track. Thus according to the impulse momentum theorem, there must be no impulse. Yet a nonzero force acted over the time interval for one rotation around the track. How can the impulse be zero?

7. Problem 1
In a crash test, an automobile of mass 1,500 kg collides with a wall. The initial and final velocities of the automobile are vi = i m/s and vf = 2.6i m/s. If the collision lasts for 0.150s, find the impulse due to the collision and the average force exerted on the automobile.

9. Problem 2
A kg baseball is thrown with a speed of 40.0 m/s. It is hit straight back at the pitcher with a speed of 50.0 m/s. a) What impulse is delivered to the baseball? b) Find the average force exerted by the bat on the ball if the two are in contact for 2.00 x 10-3 s.

11. Problem 3
An estimated force-time curve for a baseball struck by a bat is shown. a) Determine the impulse delivered to the ball. b) Determine the average force exerted on the ball. c) Determine the peak force exerted on the ball.

13. Problem 4
A 3.00 kg steel ball strikes a wall with a speed of 10.0 m/s at an angle of 60 degrees. It bounces off with the same speed an angle. If the ball is contact with the wall for 0.200s, what is the average force exerted on the ball by the wall?