Physics: Buoyancy (Float or sink)

Density
Objects like marbles, coins and stones are more dense than water. Their tiny molecules are really close together. When you put them in water, they sink to the bottom.
But objects like corks, wood and sponges are less dense than water. Their tiny molecules are further apart so they float on water. Objects that are hollow (with air inside) also float. This is because air is less dense than water.
The shape of an object matters too. When more of the surface of an object is touching the water, the object floats better. Let’s try that next.
Does the Shape Matter?
Buoyancy:
When more of the shape is touching the water it is more likely to float. The object pushes against the water, but the water pushes back! If lots of the object is touching the water, the water will push back enough to make the object float! This means the object is buoyant (even if the material is dense).
Surface Tension:
The surface tension of the water is holding its molecules together strongly. The pin floats on top of the surface!
Soap, detergent and washing up liquid break up the bonds between the molecules and makes the surface tension weaker.
The surface tension breaks and the pin can fall through!

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Indrajeet sharma

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