Here is the set up.
我有一个天平 两个完全一样的烧杯 烧杯里会放上相同质量的水
I have a balance and two identical beakers, which I fill with exactly the same amount
of water, except in one of the beakers there is a submerged ping pong ball tethered to
the base of the beaker.
And in the other there is an identically sized ball but made of acrylic.
So it is denser than water and it is supported by a thread.
Now I want you to make a prediction.
If I were to release this balance and allow it to rotate freely, which way do you think
it would tip, toward the acrylic ball, toward the ping pong ball or would it remain perfectly
You can make your selection by clicking on one of the on screen annotations or clicking
a link in the description.
>> If they are both displacing the same amount, like, I think it won’t rotate.
So, yes, it will not rotate.
>> Stay balanced.
>> The ping pong ball does have mass, albeit not very much.
I would predict that this end will sink.
>> I almost feel like this end would lift, because it is lighter than … but it wouldn’t
be pulling, because it is tethered to the lever.
I don’t know.
>> I am thinking it would go this way.
I am thinking because of the tension that is pulling this up.
所以我猜 如果你把这些力合起来 这边就更重一些
>> So I guess if your summing the forces, this one is more.
So then this is going to rise.
So I just switched my mind.
I am going to go with this one is going to rise.
但是 我的意思是这边 它似乎没有做任何力 因为
>> But, I mean, it seems like this shouldn’t be contributing any force to this side, because
it is suspended and the forces are balanced.
>> That means you would have more of a normal force on this side and it would tip that way.
>> It will tip down on the ping pong ball side?
>> Yeah, definitely the ping pong ball side.
That is so weird.
>> So now you think it is going to up on this side and down on this side.
>> Are you ready?
3 2 1
Three, two, one.