Kind: captions
Language: en
[Applause]
This is the final installment of the
beaker ball balance problem. So, if you
haven't seen the first part, you should
probably watch that now. The link is in
the description.
Now, assuming you have seen it, you know
that the balance tips towards the
hanging acrylic ball when weighed
against a beaker with a submerged
ping-pong ball. But what would happen if
instead of tethering the ping-pong ball
to the base of the beaker, it was
instead submerged by my finger? I posed
this question in the last video and you
responded with thousands of comments.
13% of you thought that the acrylic ball
beaker would be heavier. 29% thought the
ping-pong ball beaker would be heavier
and 54% of you thought that they would
be balanced. So now let's see what
actually happens in three, two, one.
It's perfectly
perfectly balanced. But why is this the
case? Well, just as in the previous
experiment, both balls displace the same
amount of water, and so they experience
the same upward buoyant force equal to
the weight of water they displace.
Therefore, there are equal and opposite
downward forces on the water, making
both be heavier by this amount. And our
answer could stop here. But if you're
wondering why this result is different
from the previous case, consider that in
the first part, the downward force on
the ping-pong ball side was counteracted
by the upward tension in the string. But
not anymore because there is no string.
Instead, the downward force from my hand
is equal to the buoyant force minus the
weight of the ping-pong ball. So that
overall both beers get heavier by the
same amount. It's just the weight of
water displaced by the ping-pong ball or
the acrylic ball because it has the same
volume. I hope you enjoyed this
experiment. If you've got another way of
explaining this, please let me know in
the comments.