Ch.7 Linear Momentum and Collisions

(Use a pompom instead of marshmallow.)

7.1 Momentum Moving objects have momentum. Same momentum: (2m) v = m (2 v ) Because momentum is the product of mass and velocity, an object's momentum changes whenever its mass or velocity changes. Sometime p is referred to as linear momentum, as opposed to angular momentum ( of a rotating object).

Momentum is a vector quantity. The momentum vector points in the same direction as the velocity vector. Both objects have the same mass, 1 kg, and both hit the floor with the same speed, 4 m/s. Since the ball bounces, its change in momentum is double.

https://youtu.be/3tH1btwdss4

The waterwheels used in gold mining operations during the California Gold Rush were not very effective. Lester A. Pelton designed a curve-shaped paddle that caused the incoming water to make a U-turn upon impact. The water “bounced,” increasing the impulse exerted on the waterwheel. https://youtu.be/3Oe8YAJ9eSQ

Kinetic Energy Momentum Formula Units Scalar or vector?

Total momentum is a vector sum: The momenta of objects headed in opposite directions can partially or totally cancel one another. Thus, it is possible for system of several moving object to have a total momentum that is positive, negative, or even zero. Momentum of ducks: Momentum of goose: Total momentum of system:

p. 233 7.) it doubles 8.) its the same 9.) momentum doubles, KE quadruples 10.) No; momenta can cancel, but kinetic energy is a scalar quantity that cannot cancel.

7.2 Impulse A force acting for a time produces an impulse. An impulse changes an object's momentum. Pelton wheel:

Use the average force, Fav, and the time over which the force acts, t, to analyze problems.

If the change in momentum occurs over a longer time, the force of impact is smaller: If the change in momentum occurs over a smaller time, the force of impact is larger:

Applications: https://youtu.be/IpfSPAoUUcQ

p.241 22.) change in momentum 23.) change in momentum 24.) because it doesn't increase the time of impact 25.) D<C=B<A 26. a) equal b) greater