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Experiment 2: Momentum
HERE'S HOW
Attach the momentum trap track to the
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tower at any height. Two of the holes attach
to pegs on the same level, and the third
attaches to a peg one level down. You have
to stretch the track a little to get it to fit.
Place a gumball on the little "speed bump"
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in the middle of the track. Position another
gumball at the top of the track. Have your
other hand ready to catch the gumball at
the end of the track. Let go of the gumball at
the top of the track. What do you observe?
WHAT'S HAPPENING
The momentum trap track demonstrates a few
more important physics principles. The momentum
trap looks like the 180-degree straight track, but
with one important difference. It has a little
"speed bump" in the middle of it. When you place a
gumball on this speed bump (or even in the little
trough in front of the bump) and release another
gumball to roll down from the top of the track,
the rolling gumball will collide with the
stationary gumball. The stationary gumball will
then be knocked into motion and continue down
the track, while the previously moving gumball
will now be stuck in the trough. To understand
what happened here in terms of physics, you
have to understand momentum and inertia.
Inertia is the tendency of a body to remain at
rest or in motion. It can also be thought of as the
amount of resistance to a change in velocity. The
WORK AND ENERGY
Every track and stunt also enables us to investigate
work and energy. Work is force exerted over a
distance. When you move a gumball from the
bottom of the tower up to the top with your hand,
you perform work. Moving a body requires work.
Energy is the capacity of a body to do work.
Energy is required to move a body over a distance.
Energy comes in many different forms, and it can
be converted from one form to another. This
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Momentum
trap track
more mass a body has, the more inertia it has.
Since both gumballs have the same mass, they
have the same inertia.
Momentum is the combined effect of the mass
and velocity of a body. All moving bodies have
momentum. A fundamental rule of physics says
that momentum is always conserved when two
bodies collide. When the gumballs collide, the
momentum from the moving gumball is
transferred to the stationary gumball, causing the
latter to move. The first gumball loses its
momentum and slows down. This describes a
perfect elastic collision. If the bodies were to
deform, or change shape, on impact, the result
would be different. This is an inelastic collision.
The momentum trap can also be used to show
how a gumball must have a certain amount of
momentum if it is to make it over the hill. If it has
too little momentum, it will get stuck in the trap.
gumball machine demonstrates two types of
energy: potential energy and kinetic energy.
Potential energy is stored energy. Kinetic
energy is the energy of motion. The gumballs at the
top of the machine have potential energy. When a
gumball starts rolling down the track, its potential
energy is converted into kinetic energy. At the
bottom of the track, it has less potential energy
than at the top. You must put energy back into it
with your hand by raising it back up to the top.
"Speed bump"
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