Kind: captions
Language: en
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now at some point growing up most of us
have been captivated by one of these a
slinky but recently I found out one of
the most mesmerizing things about how it
moves is something I'd never seen before
how it
falls so what's so surprising oh about a
falling
Slinky was what I expected well to help
explain is phys just Rod cross the idea
is that I hold the top end of the slinky
like this and then let the bottom end
dangle so the slinky is dangling freely
and then I'm going to drop the slinky
but I want you to predict what's going
to happen will the top end fall first
will the bottom end fall first will both
ends fall together or will the two ends
approach each other in the middle that
is a tough
question when I Let Go what does the
bottom do
shoot up it's going to fall it's grabing
it's actually going to fall bottom goes
up top goes down it might come up
together you're going to see the top
come down to the middle and the bottom
come up to the top come to meet it and
then drop the Top will accelerate faster
than the bottom I reckon that bottom
will stay there this will come down to
there and then they go all right well
why don't we give it a shot here I want
you to to try to watch the whole Slinky
as it falls to see what it's doing count
it down right three 3 2
1 the problem is it's a bit hard to tell
with the naked eye just what's happening
no IDE think it came up you bottom come
up I couldn't be sure it's all too fast
yeah to really appreciate the physics
involved you need to see it in slow
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motion oh
oh gosh that's great that's weird that's
unbelievable it does it does stay
there just stays there like in midair
it's suspended what yeah it doesn't move
at all how does that work how does that
work how do you explain that well you've
got to look at what's happening at the
bottom end gravity is pulling the bottom
end down tension's pulling the bottom
end up the two forces are equal and
opposite so the bottom end remains at
rest then I let go at the top end the
tension in the spring changes but it
propagates down the spring coil by coil
until it reaches the bottom end and that
takes about a quar of a second and then
the bottom end Falls so the tension
doesn't actually change at the bottom
end until the rest of the slinky has
collapsed correct the same principle
applies to sporting equipment like
tennis rackets or golf clubs when
contact is made with a ball a wave
travels up the shaft so the golfer's
hands don't feel the hit until after the
ball is already on its way to the hole
now as a final extension on this
experiment we've tied a tennis ball to
the base of the slinky we're going to
drop it and see what happens this time
incredibly the same thing happens that's
because the slinky has simply stretched
further and reached a new equilibrium
where the gravitational force down
equals the tension force up it didn't
make a difference is cing ch but that's
what makes physics so interesting that's
why I keep doing experiments like
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this