What causes milk to rise up when we boil it?

Milk contains mostly water, proteins and lactose (milk sugar). When we boil milk, the fat, sugar, proteins and minerals get separated. Since they are lighter than milk they collect on the surface in the form of cream.

During heating some amount of water gets converted into vapour and the bubbles of water vapour rise to the top The vapour gets trapped in the creamy upper layer. As the milk is heated further the water vapour expands and thick foam is produced on the top.

As the milk is boiled continuously the water, which boils at 100 degrees Centigrade, produces more water vapour and pressure builds up in the boiling milk so that the vapour pressure raises the creamy layer. So the milk pushes the creamy layer out and milk spills out.

How can we test the purity of honey?

A cotton wick dipped in pure honey when lighted with a matchstick burns and shows the purity of honey. If adulterated, the presence of water will not allow the honey to burn, If it does, it will produce a cracking sound.

Generally honey is adulterated by adding a syrup of jaggery. Pure honey does not dissolve in water but impure honey dissolves. So to test it mix a spoon of honey in a cup of water and find out whether it dissolves to check its purity.

What makes the earth rotate?

The answer is Earth has not stopped rotating

Earth rotates because of leftover momentum from the solar nebula that all of the planets and the Sun formed within.
The Solar System, and indeed the Galaxy, were formed by the condensation of a rotating mass of gas.
Each molecule in the cloud had its own momentum, and as they came together, their momentums added up, and needed to be conserved.

Conservation of angular momentum meant that any bodies formed from the gas would themselves be rotating. As frictional and other forces in space are very small, rotating bodies, including the Earth, gradually recuces the rotation speed which is approximately 30 seconds per centuary

Why is the ocean blue?

When sunlight hits the ocean it is scattered by the water molecules that make up the ocean. Sunlight is made up of all of the colors of the rainbow (red through violet). Water molecules scatter blue light the most. This makes the ocean look blue.
Sometimes the ocean doesn't appear blue! Many parts of the ocean look green. This is because the blue we would normally see is mixed with the yellow coloring of floating plants...blue and yellow make green!

Another example of water not looking blue is the Yellow Sea. It looks yellow because of the great amounts of yellow mud carried into the Sea by rivers.

Does wind have an effect on radio waves?

Radio waves have a long wavelength. Wind cannot affect radio waves because the air particles associated with wind are far too small for the radio wave to bounce off of. Radio waves can only bounce off of large objects.

Can we control the movement of hot air balloons?

Hot air balloons rises up because of the fundamental property of the hot air filled in them; air when heated becomes lighter (less denser) than the surrounding cold air. It is driven by breeze and so there is no control over the flight path. Moving up is controlled by heating the air with the help of burners uspended beneath it. As a result, the balloon rises to find its equilibrium with the surrounding air. Coming down is controlled by releasing the hot air from the balloon. Hot air balloon should be operated after studying the weather and making sure there are no strong winds.

We all know fish lives in sea water,Can the fish live in puredistilled water?

The skin of the fish is a semi permeable membrane across which water can diffuse from one side to the other through osmosis. If the fish is in distilled water, there is an osmotic flow of water from outside the fish to the inside because the salinity of the fish body is higher than that of water. Thus dilution of the body fluids of the fish occurs due to more amount of water moving inside and even blown out if the fish is in distilled water for a very long period of time.

Why is it easier to tear wet paper than dry paper?

Tearing a paper involves overcoming the cohesive force between the cellulose fibres by which the paper is made up of . In the case of dry paper this force is high and hence tearing it is not very easy. However, the cohesive force becomes weakened in the presence of water.

This is the same way table salt dissolves in water due the weakening of the electrostatic attraction between the positively and negatively charged ions. Once dipped in water, the water molecules can easily flow into the spaces between the fibres, weakening the cohesive force between them and making them susceptible to easy tearing.