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HOW IT WORKS:

Denisty is the amount of space something takes up per volume and when you add more mass to the same amount of space being taken up you can change the density of a liquid. When you drop a raw egg into fresh water the egg doesnt displace enough water making the egg more dence then the water around it. Creating an unbalanced force which sends the egg to the bottom of its container. When you add 4 tsp of salt to 250 ml of water and stir, the salt crystals break down into molecules and and fill in the holes inbetween the water molecules. The solution now has more mass in the same space or volume, which changes the density of the water. When you add the egg to the salt water you displace the same amount of water but that space has more molecules in it and the egg becomes less dence then the salt water around it. When you slowly add fresh water to salt water the less dence fresh water floats on top of the more dence salt water and you create a dencity colum of water. The egg sinks through the less dence fresh water and floats on the more dence salt water. To make anything that doesnt float, such as a bowling ball that doesnt float, you just have to increase or lower the density of the liquid you want the object to float in.