You overhear one of your fellow swimming instructors telling a kid who
is having trouble floating in the water, "Try blowing as much air out of
your lungs as possible; that way you will weigh less so the water will
have less weight to hold up." Is that true? Is it good advice?
You are the one-person audience for a practice run of a ten-minute
presentation that your friend is giving in class in 10 minutes. Readily
available to your friend are these materials (show the students a pile
of stuff including some masking tape and a metal rod with a moment of
inertia about an axis perpendicular to the rod that is many times
greater than the corresponding moment of inertia of the laser pointer).
Your friend has put together a nice power point presentation and needs
to point at a few things on the screen with a laser pointer, but, during
the practice run, the bright dot on the screen is jiggling about so much
that you cannot tell what your friend is pointing at. What advice would
you give your friend that would allow your friend to use the laser
pointer to create a nice steady bright spot on the screen while still
being able to move it about steadily and pretty quickly?
(You might be able to find a newspaper article to support this one.)
You heard that a fire got started because a person plugged a space
heater into an extension cord (that was in good condition). Your friend
says that the story is ridiculous and argues that the wire in the walls
of the house is so much longer than the extension cord that a few more
feet of wire wouldn't make any difference. Your friend argues that the
space heater probably malfunctioned and that the firefighter who
attributed the problem to the extension cord doesn't have a good
understanding of basic physics. Is your friend right?
You overhear a conservation between two friends. One tells the other
about an accident in which two cars collided head on. The speaker says
there were no skid marks, suggesting that neither driver braked. The
speaker says that the collision involved a big old car and a little new
car and that the little new car was pushed way back from the point of
impact and smashed up badly while the big old car kept old kept on going
forward for awhile and sustained little damage. Your other friend says,
"That can't be true--it would be a violation of Newton's 3rd law?" Can
it be true?