A scientist weighs a jar of sleeping flies. Then, he shakes the jar to wake them up. While flies are flying in a closed jar, the scientist weighs the jar again. Does the jar weigh less when the flies are flying?
You have a balance beam, the kind of scales that tips from one side to the other, depending on the weight on each side. 10 kg of the iron-nails balanced on the scales by iron weights. The balance beam submerged in water. Are the scales in balance?
You have a balance beam, the kind of scale that tips from one side to the other, depending on the weight on each side. On each side is a beaker, half-filled with water. The sides are in balance. Now, on the left side, you submerge a Ping-Pong ball suspended by a string. On the right side, you submerge a steel ball of the same volume as the Ping-Pong ball suspended from a crane.
You may ignore the mass of the strings.
Does the balance beam tip to the right, to the left, or does it remain unchanged?