3. What is force? Describe different type of forces with example and diagram,
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Project 2
Date of Submission: 18th January 2021
Answers
Explanation:
Frictional force:
You have learnt that a force is required to stop the movement of a body in motion. Then why does a swing not continue to move forever once you have given it a push? And why does a ball not roll endlessly once you have kicked it, even if no force is applied to stop it?
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This is because when (the surface of) one body moves over another, frictional force acts in a direction opposite to that of the motion. Frictional force always opposes motion, trying to stop the movement of one surface over another. However, how great the frictional force is depends on the nature of the two surfaces in contact.
This will become clearer after you do the following activity.
Frictional force
Place one end of a strip of cardboard or plywood on a block of wood or a brick. Place the other end on the floor, as shown in Figure 8.5. Place a small rubber ball near the top, and let it roll down on to the floor. Note the distance the ball travels along the floor.
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Try out this activity on different types of floors (for example, a tiled floor and a carpeted floor). Note the distance the ball travels each time. Try to keep the cardboard inclined at the same angle each time. You will see that the ball travels farther on a smoother floor.
No surface is perfectly smooth. Even the smoothest surface has tiny bumps and holes all over. When two surfaces move over each other, the bumps and holes on both get in each other’s way. This is what causes friction. Obviously, the smoother the surface, the lesser is the frictional force. That is why a ball travels a greater distance over a tiled floor than over a carpeted floor.
Static and Kinetic Friction:
Frictional force does not only depend on the nature of the surfaces in contact. It also depends on whether something is moving over a surface or it is stationary.
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Activity:
Try to push a heavy dictionary over the surface of a table. Push gently first, using one or two fingers. You will feel the frictional resistance. Keep increasing the force you apply until the dictionary starts moving. Does the resistance offered by friction, or the frictional force, seem to decrease when the book starts moving?
When a force is applied to move a body, frictional force resists the movement. As the force increases, the frictional force also increases, until the force applied becomes greater than the frictional force. Just as the force applied becomes greater than the frictional force, the body starts moving.
And as the body starts moving, the frictional force decreases. It is as though frictional force has limited strength, and as long as the force applied does not cross this limit, frictional force flexes its muscles and acts like a bully. When the force applied manages to get past this limit, frictional force loses heart and becomes weaker.
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Remember two things in this context.
1. A body starts moving when the force applied is greater than the frictional force.
2. Static friction, which acts when a body is stationary, is greater than kinetic friction, which acts when a body is moving.
