Chap 6 What is MOMENTUM? Units: kg m/s

Newton’s 2nd Law written in terms of change in momentum

What is IMPULSE? Units: N s

Force on a car versus time for a typical car collision. area = I Time Force Force Force on a car versus time for a typical car collision. Time

BOXING AND BRAIN INJURY Bare fists were used in the past, now fighters wear padded gloves. Why? Other examples with the same application: Car bumpers, Air bags, Seat belt

Impulse-Momentum Theorem From Newton’s 2nd Law: Impulse-Momentum Theorem

Quick Quiz A car and a large truck traveling at the same speed collide head-on and stick together. Which vehicle undergoes the larger change in the magnitude of its momentum? the car the truck the change in the magnitude of momentum is the same for both impossible to determine without more information

Impulse-Momentum Theorem Force when the bodies are in contact Velocities before and after the contact (no contact is happening)

Quick Quiz The same force F is applied to different bodies originally at rest for different amounts of time. The diagrams below show the results (after the force ceased). m 3m 2m x0 = 0 3.0v 2.5v 1.0v 1.5v (A) (B) (C) (D) Rank the IMPULSE for each diagram from the greatest IMPULSE to the least IMPULSE applied. (E)

Collision of astronauts

IMPULSE HAPPENS DURING THE COLLISION During a collision (only while the objects are in touch) the objects receive an IMPULSE (I) (3) Units of Impulse I = [ N . s] I2 I1 Impulse on astronaut 2 Impulse on astronaut 1 IMPULSE HAPPENS DURING THE COLLISION

Bouncing Ball

Conservation of momentum

Two skaters of different masses prepare to push off against one another. Which one will gain the larger velocity? The more massive one The less massive one They will each have equal but opposite velocities. The net external force acting on the system is zero, so conservation of momentum applies. Before the push-off, the total initial momentum is zero. The total momentum after the push-off should also be zero.

Collisions

Glancing collisions

Two lumps of clay of equal mass are traveling at right angles with equal speeds as shown, when they collide and stick together. Is it possible that their final velocity vector is in the direction shown? yes no unable to tell from this graph No. The final momentum will be in a direction making a 45o degree angle with respect to each of the initial momentum vectors.

Two cars of equal mass Collide at right angles to one another in an intersection. Their direction of motion after the collision is as shown. Which car had the greater velocity before the collision? Car A Car B Their velocities were equal in magnitude. It is impossible to tell from this graph. Since the angle with respect to the original direction of A is smaller than 45º, car A must have had a larger momentum and thus was traveling faster.