Question

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Why do we say that materials in our world are mostly “empty space"?

Why will a block of iron float in mercury but sink in water?

A ship sailing from the ocean into a freshwater harbor sinks slightly deeper into the water. Does the buoyant force on the ship change? If so, does it increase or decrease?

An old man sells you a solid gold 1-kg statue for a very reasonable price. When you get home, you wonder whether or not you got a bargain, so you lower the statue into a container of water and measure the volume of displaced water. Show that, for pure gold, the volume of water displaced will be 51.8 cm3.

Answer 1

1. Materials are basically made up of atoms. These atoms have a nucleus in the core built up of neutrons and protons held together by a strong binding force. The nucleus is extremely tiny and can be modelled as a sphere of radius of the order of 10^-15 m. There is another type of subatomic particle called electron, even smaller than protons and neutrons, that revolves the nucleus. Together they form an atom but the electrons revolve the nucleus with a radius much larger than the size of the nucleus, leaving a lot of empty space in between. This is why we say that materials are mostly made up of empty space.

2. A block of iron will float on mercury but not on water because density of mercury is greater than density of iron but density of water is lesser than that of iron.

3. Buoyancy force is directly proportional to the density of the fluid. Salt water has higher density than fresh water this is why buoyancy force in salt water is higher than fresh water. In fresh water the buoyancy force can not give more force against the gravitational force of the ship as compared to salt water and this is why the ship sinks a bit deeper.