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# How Did We Use Energy?

Boxes are carried, heavy furniture is shifted, and goods are transported over steep hills. People learned early in their existence how to simplify the work. They crouched down for lifting a box; mountain trails and mountain passes were made in widely curved serpentines; and pulleys were used in storage halls and harbours. Soon this knowledge was used in different ways. For example, a crown cap fits tightly on the bottle, and it is easy to open it with a bottle opener.

## Why do mountain passes have serpentine roads?

Any work can be done in many ways. What matters is how it is done. We can climb the mountain in two ways. If we take the shortest route, we need to apply a lot of force. If we gradually ascend towards the top using the serpentine roads, it takes long, but saves energy. It is based on the law of physics: Work = Force >< Distance.

## What is pulley?

A pulley is a device used to lift heavy objects. It is made with a cable and a wheel of different sizes. Here again, the law ‘Work = Force x Distance’ is applicable as in the case of serpentines. Here ‘distance’ means the length of the cable. The cable is wound around the wheels.The more the number of wheels, the smaller the force to be applied. We can find such pulleys on sailing ships for hoisting the sail. They are also used at construction sites to lift beams or other construction material. Earlier, pulleys were used to put heavy ship boxes in storage spaces high above the ground.

## Did you know…

Even the Egyptians used pulleys while building the pyramids for putting the stone blocks weighing several tons one above the other?

Friction is important? Without it we cannot apply brakes.

Hovercrafts travels very fast because the friction between the boat and the water is reduced by an air cushion?

Earlier the rollers of weaving looms were called ‘pulls’? The name ‘pulley’ is derived from this word.

## Why is it difficult move heavy furniture?

Heavy furniture exerts a high pressure – force per unit area – downwards. If both the contact surfaces of the furniture and the surface of the floor are very rough, the surfaces adhere to each other. To move the furniture we have to overcome this force known as static friction. It is smaller if the surfaces are smoother. During movement, it gets converted into dynamic friction. It is easier to transport heavy objects on wheels. Forces of friction always produce heat. In the stone age, human beings used this heat to make fire.

## Why do we crouch down to lift a heavy box?

The body’s centre of gravity normally lies near the belly button. When we bend forward and lift a heavy box, the centre of gravity of the ‘body plus the box’ lies far away from our body. This puts a lot of pressure on the backbone, and the back muscles resist this. In contrast, when we crouch down and get up with the box, the centre of gravity remains near the body. This puts less pressure on the backbone and helps keep our backs healthy.

## How does a bottle opener work?

A bottle opener is a simple lever. It intensifies the force with which we remove the crown cap of a bottle. Levers are mostly rigid, rod-shaped objects that have a fulcrum at one place. The longer the arm of the lever, the lesser the force required to do the work. The law of physics ‘Work = Force x Distance’ is applicable here too. The bottle opener is a one-sided lever. The longer the arm of the bottle opener, the easier it is to open it. Other examples of levers are pliers, scissors, crowbars, wrenches, paper punchers, and door handles.