My Science School

What you do:

• Turn on the tap.
• Watch the water flow.

What you see:

The stream of water is initially of the same size as the opening of the mouth of the tap but it decreases in size as it flows.

Why does this happen?

Surface tension tends to hold the water in a solid stream at the top but as it falls, its speed increases because of the pull of gravity.

When the flow of water is continuous, the amount of water passing through any point should be the same. The amount of flow is determined by the cross sectional area of the stream multiplied by the speed of flow of the water. As the speed of the water increases due to gravity. its size reduces.

Picture Credit : Google 

 

What you need:

A glass and a vessel with tea What you do:

Hold the vessel high above the glass and pour the tea into it. What do you find? Bubbles form on the surface of the tea inside the glass. Next hold the vessel close to the glass and pour the tea into it.

What do you find?

Bubbles don't form on the surface of the tea inside the glass.

What's the reason?

Due to surface tension, the surface of a liquid behaves like a stretched membrane or skin'. When you pour tea into the glass while holding the vessel close to it the tea falling gently cannot penetrate the skin of the tea in the vessel. But when you pour it from a great height, it strikes the surface of the tea in the glass with great force. The skin breaks trapping air, which bubbles back to the surface.

Picture Credit : Google

What you do:

• Open your mouth wide and blow air into your palm. Observe.

• Then purse your lips and blow air into your palm. Observe.

What you find:

The air is warmer when you blow with your mouth wide open.

Why?

The temperature of the air coming out of the open mouth is more or less the same as that of the body, and hence it is warm. When you purse your lips, the air gets compressed and comes out in a thin stream but once, outside, it expands and cools. Another reason for the difference is that the fast moving stream of air draws in cool air from the surroundings.

Picture Credit : Google 

What you need:

A bicycle and a friend to ride it.

What you do:

 • Ask your friend to cycle fast.

• Watch the upper and lower spokes of the wheels.

What you find:

The spokes of the wheels that are below are clearly visible but the upper spokes are a blur. Does it mean that the top of the rolling wheels moves faster than the bottom?

Yes. This happens because while the wheels are rotating on their axle, they are also moving forward along with the axles. At the top, the two motions are in the same direction but at the bottom the rotation is in the reverse direction.

Picture Credit : Google