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Unit 2: Motion Page 18
Take a look at your marks. See Remember momentum?
how they get farther and farther Momentum can be defined as
apart as the ball continues to inertia in motion. Something
accelerate? Your ball was must be moving to have
constantly increasing speed and as momentum. Momentum is how
such, it was constantly hard it is to get something to stop
accelerating. By the way, would it or to change directions. A moving
have mattered what the mass of train has a whole lot of
the ball was that you used? No. momentum. A moving ping pong
Gravity accelerates all things ball does not. You can easily stop a
equally. This fact is what Galileo ping pong ball, even at high
was proving when he did this speeds. It is difficult, however, to
experiment. The weight of the ball stop a train even at low speeds.
doesn’t matter but the size of the
ball might. If you used a small ball Mathematically, momentum is
and a large ball you would mass times velocity, or
probably see differences due to Momentum=mv.
friction and rotational inertia. The
One of the basic laws of the
bigger the ball, the more slowly it
universe is the conservation of
begins rolling. The mass of the
momentum. When objects smack
ball, however, does not matter.
into each other, the momentum
that both objects have after the
collision, is equal to the amount of
Experiment: Ball Launcher momentum the objects had before
the crash. Once the two balls hit
This is a satisfyingly simple activity the ground, all the larger ball’s
with surprising results. Take a momentum transferred to the
tennis ball and place it on top of a smaller ball (plus the smaller ball
basketball… then release both at had its own momentum, too!) and
the same time. thus the smaller ball goes zooming
to the sky.
Instant ball launcher!
Do you see how using a massive
You’ll find the top ball rockets off object as the lower ball works to
skyward while the lower ball hit the your advantage here? What if you
floor flat (without bouncing much, shrink the smaller ball even more,
if at all). Now why is that? It’s to say bouncy-ball size?
easier to explain than you think… Momentum is mass times by
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