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# Daily Archives: December 3, 2011

## Weight and inertia on moon

Say True or False; An object on the Moon weights 1/6 of what it weights on the Earth. Therefore, the object has less inertia on the Moon.( Justify your answer)

Inertia depends on mass and not on weight. The weight on moon is less not because of a decrease in mass, but due to the decrease in the acceleration due to gravity on the surface of moon.

Inertia depends on mass and there is no change in mass when a body is taken to moon. Therefore the inertia of a body is same on moon as that on earth or anywhere else in the universe, even in a gravity free space.

## Physics of Diving

When a high diver in a swimming event springs from the board and “tucks in”, a rapid spin result. Why is this?

Answer: This is the consequence of conservation of angular momentum.

The angular momentum of a body is the product of Moment of inertia (A measure of rotational inertia and it depends on the mass as well as distribution of mass about the axis of rotation. Farther the masses, greater will be the rotational inertia) and the angular velocity (The speed of rotation)

The angular momentum of a body remains unchanged in the absence of any external torque.

When the diver dives, he is giving his body a turning and takes off with his limbs stretched. In the stretched position, the moment of inertia is more. When he “tucks in”, the moment of inertia decreases. But since this happens without any external torque, it would result in an increase in angular velocity so as to keep the angular momentum constant.

## Lightning Conductor – Working and Theory

How does a lightning conductor work ? Please explain

Answer: Lightning conductor is a conducting rod with sharp spikes erected at the topmost region of  a building to be protected. The rod is connected to earth via thick copper strips. The contact with earth is kept well conducting.

The lightning conductor protect the building in two ways

1. It avoids the chance of a lightning strike by corona discharge. (The opposite charge induced by the charged clouds are sprayed back to the clouds through electric wind and this avoids the potential difference getting developed to a higher value.)
2. If a lightning strikes, it provides a conducting path to earth without affecting the building or the inhabitants or the appliances inside.

## The Physics of a Pressure Cooker

How does a pressure cooker work? What is the Physics behind it?

A pressure cooker develops a very high pressure when water boils inside. At high pressure the boiling point of water also rises and therefore food gets cooked at a higher temperature. Therefore the food materials are cooked well and faster than at normal temperature and pressure.

A pressure cooker is extremely useful in hilly areas where the pressure is very low and the boiling point is less for water. AT a lower boiling point, cooking is very difficult as proper cooking will not take place. When a pressure cooker is used, it increases the pressure as well as the boiling point and the food materials can be cooked well.