Thursday, April 16, 2009 - Block 2

Collected RA 4.4
Reviewed Newton's 3rd Law

Explained problem of boxer hitting paper - Can he exert a force of 200 N on paper? Showed using F = m*a that it was not possible if paper hung in air, but would be possible if paper was against a wall.

To examine the magnitude of the force, look what happens. When hit at the same speed, the "free paper" accelerated and the fist carried through. Not enough force of paper on fist to stop the fist. When against the wall, the paper exerts enough force on the fist the stop the fist. If the paper exerted an even greater force, the fist might rebound.

Showed video clip from Independence Day. Hollywood does not understand the 3rd Law.
Example of flies in a jar.
Helicopter on force plate.

Handed out RA 4.5 due tomorrow.
Handed out CD 6.1 due for last time on Monday. Explained that I wanted not just arrows but descriptions of the forces written in the margins for the last problem on the front side.