When you try to push or pull a heavy object it appears as if the floor pulls it back. This backward pulls called friction.
Friction is useful as well as harmful. If there is no friction we cannot walk. The vehicles slip away and fall. A nail driven into the wall cannot be held by it and easily comes out. Writing with a chalk on a smooth blackboard is difficult than on a slightly rough black board because friction offered by the rough surface helps us to write. We could apply the brakes of the bicycles because of friction only. A match stick can be lighted because of the friction offered by the rough surface on their side of the match box.
In some cases, friction is harmful.
It prevents easy movement of wheels in machines. The machines break down easily because of the frictional force. It produces a lot of heat.
Frictional force can be reduced by applying lubricants like castor oil or grease. You might have seen the mechanic applying oil or grease to your bicycle. Smooth surfaces reduce friction. Write some examples where friction makes the work difficult.
We do different types of work everyday. When you say, ``I am working,’’ it means that you are doing something. When you push or pull an object, you do some physical work. Whenever we use a force to move a thing we say that work is done. In scientific terms, work is done only when something is moved to a certain distance.
Conditions to do mechanical work
1) Some force has to be applied on the object
2) The applied force should move the object in its direction or change its shape
All living things need energy to work. The food we eat as fuel and enable us to work. Like food, fuels like petroleum, coal etc., also give energy.
The capacity to do work is called energy.