Do you get lighter when you put your hand in a bucket of water?

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CONFIRMED

I was listening to Dear Hank and John, a podcast where two brothers offer dubious advice in a fun, lighthearted way (while somehow also being thoughtful and comforting). In it, they got a science question that I couldn’t help falling in love with. The question can be posed like so:

Suppose you are on one scale, and a bucket of water on another. If you submerge your hand in the water, will the bucket’s scale get heavier and yours lighter?

This is the best kind of science question - simple but elegantly deceitful in the way it plays your intuition against you. After all, if you add something to the bucket of water, you would expect it to get heavier. Easy. But then, you think, have I gotten lighter? I don’t feel lighter. And mass can’t come from nowhere … so … does that mean the water’s scale won’t change because mine won’t?

And so the loop starts. You spin yourself in circles, overthinking basic physics and questioning your intellect. Does the water support my weight? Do I support my weight? If I don’t support myself, who or what does? Am I being supported at all? Am I just a burden on the world, a weight that pushes on the scales of those around me, only to be borne in the same silent dissatisfaction offered by the water? Or maybe the water likes supporting me? After all, I’ve made its day more interesting and enjoyable, and given it a purpose, right? Right?

Clearly, this is a question that needs answered. Luckily, the internet is on it - I love the answer posted by this engineering student:

@hankgreen @johngreen my explanation for the water bucket problem.
Not a physicist, just an engineering student
-Jannes

(Sorry for the bad handwriting) pic.twitter.com/Wx3cFbWdKs

— Ultraschrall (@JSchrall) September 21, 2021

Their drawing and reasoning is so clear and conveys the problem at hand (get it?) so well, it’s completely convincing. The answer is yes, if you place your hand in the bucket of water, its scale will get heavier and yours lighter. And they even managed to extend the question: what if the bucket has something other than water? It turns out a denser liquid than water will increase the amount of weight taken from your scale and added to the bucket’s scale, and a less dense liquid will decrease the weight moved from one scale to another.

That’s 100% right. This kind of creative question with a small, revelatory answer is among the small revelations that keep me, as a scientist, falling in love with science again and again.

But this is still all theoretical. To truly satiate our curiosity we need data. We need a demonstration. I am here to offer that demonstration.

The Setup

Because my partner and I are avid bakers, and I am a coffee lover, we have 2 kitchen scales, sensitive to below one gram. This means we can scale down our experiment to fit on a kitchen counter.

Materials

None of the objects I gathered are particularly rare, so this should be accessible to nearly everyone.

Process

Assemble the rig according to the picture below. Once assembled, turn on the scales and make sure they are tared - they both read 0 grams.