If you add a large fish of 2 kilograms to an aquarium with 20 liters of water, which is on a scale, does the weight on the scale change? If yes, with 2 kg or with less? We have been puzzling over this with a group of friends for several years now and can’t figure it out. It could be that the question is always raised again if we have already had a drink and then we no longer manage to think clearly… but still. Actually, we are ready for an answer!
Answer
Dear Lutgard,
The whole will indeed weigh 2 kg more, unless water flows over the edge of the aquarium during this maneuver. After all, mass cannot be lost.
Put it to the test in the kitchen with a bowl of water and an egg that you put in it. Weigh the egg beforehand. You will see that the weight of the egg just adds up. Now do the same with something that floats, a piece of wood. That weight just adds up. Whether something sinks, floats or floats does not matter to the weight. However, the level of the water surface will rise: most when something sinks and least when something floats.
Fortunately, you can make pancake batter in any order of addition of the ingredients: whether you put milk in the bowl first and then the eggs and solids or vice versa, it makes no difference to the scale.
Kind regards,
dr. ir. Pieter Schevenels
Answered by
dr. ir. Pieter Schevenels
sound acoustics engineering
Agoralaan University Campus Building D BE-3590 Diepenbeek
http://www.uhasselt.be/
.