Concept: Gravity
Does a bowl of water weigh more with a goldfish in it than it does without the fish? This question usually provokes considerable argument. What do you think the answer is? If you said “Yes,” then you are correct! The bowl’s weight is increased by exactly the weight of the fish inside.
Suppose you nearly poke a finger into the water. Most people would guess that this would not make the bowl heavier, but it does. The bowl’s weight is increased by the weight of the water your finger displaces, as you can easily demonstrate.
Place a glass on each end of a ruler, with a pencil beneath, to form a crude balance scale. Adjust the pencil until the scale is almost, but not quite, balanced. Now plunge your finger into the raised class, taking care to touch only the water. The extra weight will immediately tip the “scale” the other way.