Friction Worksheet-10

Friction Worksheet-10

36. Why does a car stop when brakes are applied?

37. Give three factors on which the frictional force in fluids depends.

38. How has nature shaped the body of fishes to minimize air resistance?

39. A labourer has to push a heavy trunk. What should be done to reduce his effort in pushing it and  why?

40. (a) How do trees help reduce friction?

(b) Why do meteors burn on entering the atmosphere?

41. Amit was riding his bicycle. He found that he had to apply a lot of force while pedalling. Why? What can he do?

42. Give five examples to show that friction is increased deliberately.

43. Why are heat resistant tiles laid along the surface of spaceships?

44. What is meant by lubrication? Why do we lubricate the moving parts of our vehicles? Name some lubricants and where they are used.

45. What is meant by "streamlined shape"? Where and why is this shape used? To whom has nature provided streamlined body?

Answer:

36. In cars, the friction is increased by using brake pads in the brake system. The brake pads do not touch the wheels but when we press the brake level, these pads arrest the motion of the run due to friction and the wheel stops moving.

37. Speed, shape and nature

38. The shape of the fishes is streamlined to minimize water resistance, so that they do not loose much energy while swimming.

39. The labourer may put some cylindrical logs of wood under the trunk. This way the area of contact between the two surfaces is reduced. Rolling friction is less than sliding friction.

40. (a) Trees slow down strong winds and save us from wind storms.

(b) The speed of the meteor is very high. Therefore, there is a large amount of friction between the air and meteor. This generates a lot of heat and the meteor starts burning.

41. He had to apply more force because there had been more friction between the parts of the bicycle. He may apply oil to the parts to reduce the friction.

42. (a) Athletes wear spiked shoes that help them run faster in sports.

(b) Mountaineers wear spiked shoes while walking on snow.

(c) The tires of vehicles are grooved.

(d) The roads are made rough.

(e) The blackboards are made rough.

43. The spaceships are sent into the space from the rockets with a very high speed. This creates a very high frictional force between the air and spaceship. As a result, the spaceship gets heated to red hot. The heat resistant tiles save the spaceship from burning.

44. Lubrication means oiling the machines from time to time. Lubrication of the moving parts is done to reduce friction between them. Oil or grease or Graphite can be used to reduce friction in machines.

45. Streamlined shape means they are narrow in front and broader at the back. The bodies of aeroplanes, missiles and rockets are streamlined to reduce friction with air. Ships and boats have a streamlined shape to reduce friction with air. Nature has given birds and fish streamlined bodies.