Tuesday, Nov 30, 2010

Collected RA 5.1

Handed out RA 5.2 due tomorrow.

Went around the room and asked what they remembered from last class.

Show parts of video dealing with boxing, railroad cars.

Demo with blowpipes and marshmallows to show that longer cannons impart more impulse (same force, longer time) than short cannons. Actually did this yesterday.

Catching and throwing on frictionless ice both give impulse. Catching and throwing is like bouncing. More impulse if bouncing occurs. But...don't know anything about the force unless you know something about the time.

Skare's demo with happy and sad balls knocking down block.

Bouncing gives greater impulse since there is a greater change in momentum. We know nothing about the force unless we know something about the time.

Showed part of video on Pelton Waterwheel

Intro to conservation of momentum: If no net external force acts on the system, then there is no change in momentum.

Conservation of Momentum has never been shown to fail. It does not apply in cases in which there is an external force (such as gravity for a falling object).

Applied Conservation of Momentum to collisions.
Two basic types of collisions:
1. Elastic (Things bounce)
2. Inelastic (Things stick)
If there is no net external force, momentum is conserved in both types of collisions.

Demos with air track for both types of collisions.

Worked inelastic collision problems on board showing problems solving strategy.

Handed out Inelastic Collisions worksheet. Students worked on it in class and handed it in. Actually ran out of time so had students do it for HW

Handed out CD chpt 5 due for the last time on Monday. It asks for pictures, if you don't draw them then I will return the paper.