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› › › PHYSICS EXPLANATIONS
Track
without
dominos
Rubber band color may vary.
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The
domino track offers another lesson in
transfer of momentum. To set up the domino track,
insert the six dominos and the domino track post, and
place a gumball on the post. A gumball drops into
the top of the domino track and knocks down the first
domino. A chain of collisions follows, in which each
domino knocks down the next. The final domino falls
over and collides with the gumball positioned on the
post, which falls out of the track. The momentum is
transferred from the gumballs through the dominos.
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You can also use the domino track without the
dominos and post as a simple
90-degree smooth track.
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The
pendulum stunt is attached to the tower
using the angled pivot post. When a gumball enters
the cup at the top of the pendulum, it causes the
pendulum to turn on its axis and the gumball is
passed to a lower track.
A
pendulum is a weight suspended from a pivot
that can swing freely. It demonstrates center of mass
and stable equilibrium.
Center of mass is a point on a
body representing the mean (or middle) position of
the mass of the body — mass on all sides of this point
balances out. When the pendulum is stationary, it is
said to be in stable equilibrium.
Equilibrium is the
state of a body at rest or in unaccelerated motion in
which the result of all forces acting on it is zero. A body
is in
stable equilibrium if its center of mass is located
vertically above its base of support. If its center of mass
lies vertically above its tipping line (the edge of the
base), then it will wobble or fall over. The slightest
movement will make it tip over. But its stability also
depends on the force needed to push it off balance.
The pendulum has been specifically designed with
a counterweight at the bottom that offers just enough
inertia to keep the pendulum stable until the gumball
enters the cup and knocks it out of stable equilibrium.
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The
trampoline is a window into two more huge
realms of physics: springs and projectiles. To set up the
trampoline, you must stretch the rubber bands around
the trampoline ring. The notches in the ring keep the
rubber bands from slipping off. Try to evenly space the
rubber bands around the surface of the ring. The
trampoline ring attaches to the tower with a straight
pivot post. Position the trampoline at an angle such
that when a gumball falls on it, the gumball bounces
into the next track segment.
The rubber bands in the trampoline work like a
spring. When a moving body stretches or compresses a
spring, it converts its kinetic energy into potential
energy stored in the spring. Then, the spring bounces
back and pushes back on the body. The amount of
force exerted on a spring is proportional to the amount,
or distance, that the spring stretches or compresses.
The more momentum a gumball has when it hits the
trampoline, the more the rubber bands will stretch.
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