This week’s material concerns rotation. You should review Hecht 2
ed. Chapter 8
before starting this lab. The activities for this lab are varied. You will race various objects
down a slope and predict which will get to the bottom first. You will have the opportunity
to spin in the rotating chair to get personal experience of rotational motion. You can
examine the stability of some interestingly constructed solids.
EXPERIMENT A: Racing down the slope.
Suppose you have two equal mass objects both on a gentle incline. One is a glider
on an air track, the other is a ball on a straight slope. The air track and the slope
have the same slope angle. You release them at the same time and at the same
distance up the slope. Note that neither looses any significant amount of energy to
friction since the air track has very low friction and the ball rolls (not slides) down.
Which will reach the bottom first? Justify why one will beat the other, or why you
think they will be the same.
Why does a ball roll rather than slide (without rolling) down a slope? Under what
special circumstances would a ball slide and not roll as it moves down a slope? If
you could make it slide and not roll would it beat the air track?
Suppose you have two objects with the same
mass and radius, but different moments of
inertia, rolling on a flat surface at the same
linear speed. You might imagine a solid
wooden cylinder and a hollow metal cylinder.
The metal cylinder (higher density than wood)
is not solid, so it has most of its mass at the
edge giving it a larger moment of inertia.
Compare their translational kinetic energies.
Compare their rotational speeds. Compare
their rotational kinetic energies. Which has