PHYSICS [5 Mark Question Answer]

Various effects of force :

1. A force can move a stationary object.
   Example: Pulling a suitcase on its wheels.
2. A force can stop a moving object.
   Example: A ball rolling on the rough surface comes to rest after some time due to the force of friction.
3. A force can change the speed of a moving object.
   Example:We can increase the speed of a moving swing, we apply a force (push) in the direction of motion to increase its speed.
4. A force can change the direction of a moving object.
   Example:A moving bicycle changes its direction when a force is applied to steer its handle.
5. A force can change the shape and size of an object.
   Example:When we make a chapatti, a small ball of dough is changed to a flat, circular shape of a much bigger size by applying a force with the help of a rolling pin.

• Disadvantages of friction:

1. Friction produces heat which damages the moving parts of a machine.
2. Friction produces wear and tear on the contacting surfaces. This reduces the life of machine parts, tyres and shoe soles.
3. A lot of energy is wasted due to friction to overcome it before moving.,

• Ways to reduce friction :

1. Providing ball bearings or wheels between the moving parts of machine or vehicles reduce friction and allow smooth movement as rolling friction is less than sliding friction.
2. Oiling or lubricating (with graphite or grease) the moving parts of a machine reduces friction. Fine powder like talcum powder also works as a lubricant to reduce friction.
3. Polishing the rough surface reduces friction offered by it.
4. Streamlining (giving special shape to experience minimum drag) the bodies of aeroplanes, cars, boats and ships help reduce drag (fluid friction) while travelling through air or water.

Friction is a force that opposes relative motion between two bodies/surfaces in contact with each other. Although friction opposes the motion, it also makes motion possible.
Friction helps us do many things like :

• It helps us in walking. In the absence of friction, we may slip or M.
• Cars and buses are able to move safely on roads due to the friction between the treaded tires of these vehicles and the surface of the road.
• Friction allows us to hold objects with our hands.
• It allows us to write on paper.
• Friction produces heat. In winter, when we rub our cold hands, the heat produced due to friction makes our hands warm.