Science Chats Forum

To Whom It May Concern,

As we continue working on my son's science fair project, we are wondering what the answer is to a key question he has.

We are doing a basic experiment on salt water buoyancy. We are attempting to float an egg (raw and hard boiled) in a solution of salt water - ratio 20:1 salt to water. As we suspected and know from previous knowledge, we knew the 3 ounce eggs would float. Our question is, as we also attempted to float a 1 ounce marble, and a 2 ounce metal lug nut, we observed they did not float even though they weigh less than the egg. If the egg weighs more than the other two objects, why does it float, and the other objects do not? We think after some research that it has to do with the inside composition & density of the object, not so much the issue of weight. As far as I know, a 300 pound person would float in the Dead Sea, as much as a person who weighs 150 pounds,... but why? What is the basic principle of why this situation occurs? And more so,.... why do other 'solid' impermeable objects (lighter in weight) not float?

Please respond in layman's terms. ;o)

Thanks!

Sincerely,

Debby O

The answer is simply displacement. If the amount of water displaced by the object (the volume of the object under water) weighs more than the whole object itself, it will float. The marble is too small for its weight.