Question 1 Why is the surface of slide polished to make it smooth?
Question 2 Name 2 lubricants?
Question 3 Why do we sprinkle fine powder on carrom board?
Question 4 Which force gets reduced when two surfaces in contact are polished to make them smooth?
Question 5 State one way in which the friction between wheel and axle can be reduced?
Question 6 Why does oiling the axles of a bicycle make the bicycle move more easily?
Question 7 Name one example from every day life where wheels are used to reduce friction?
Question 8 Name device which is attached to heavy luggage to move it easily by pulling?
Question 9 What is lubrication?
Question 10 Why are lubricants applied to rubbing surfaces of machines?
Question 11 Explain why wheels are so useful?
Question 12 Why is lubrication important?
Question 13 How will you reduce friction between those machine parts which rub against each other?
Question 14 What is ball bearing?
- 1 (1) Friction can be reduced by making the surface smooth by polishing
- 2 (2) Friction can be reduced by applying lubricants (like oil or grease) to the rubbing surface
- 3 (3) Friction can be reduced by using wheels to move objects
- 4 (4) Friction can be reduced by using ball bearing between the moving parts of machine
(1) Friction can be reduced by making the surface smooth by polishing
The friction is due to the roughness of surface. If we make the surfaces smooth by polishing, then friction will be reduced. For example a slide in the park is polished to make its surface smooth and reduce friction. Due to reduced friction of a polished, smooth slide, children can slide down easily.
(2) Friction can be reduced by applying lubricants (like oil or grease) to the rubbing surface
When oil or grease is applied between the moving parts of a machine, a thin layer of oil or grease is formed between the two rubbing surfaces. This layer of oil separates the two rubbing surfaces a little bit due to which their interlocking is reduced to a large extent. This friction is reduced and movement becomes smooth. When oil or grease is applied to the moving parts of a machine, then their surfaces do not rub directly against each other, they rub through a layer of oil and grease .
The substance which reduce friction are called lubricants
Oil, grease, graphite and fine powder are lubricants.
The applying of lubricants to a machine is called lubrication.
Friction can be reduced by lubrication.
A well lubricated machine runs more smoothly and lasts longer.
(1) A bicycle mechanic and motor mechanic uses grease between the moving parts of these machines to reduce friction and increase efficiency.
Drops of oil are poured on the hinges of a door, the friction is reduced and the door smoothly.
(3) We Sprinkle fine powder as dry lubricant on carrom board to reduce friction.
(4) In some machines an air cushion between the moving parts is used to reduce friction. For example the frictional drag from the sea on hovercraft is reduced by a cushion of compressed air. (A vehicle or craft which travels over land or water on a cushion of air provided by a downward blast is called hovercraft)
(3) Friction can be reduced by using wheels to move objects
It is quite difficult to move a heavy suitcase by dragging it on the ground because the sliding friction between the heavy suitcase and the ground is very large. If this heavy suitcase is fitted with small wheels then it can be pulled very easily. Because when we attach wheels then sliding friction is converted into rolling friction. And rolling friction between the wheels of suitcase and ground is much less.
Friction can be reduced by attaching wheels to move the objects.
(4) Friction can be reduced by using ball bearing between the moving parts of machine
Ball bearing is a device which consists of a ring of small metal balls. The small metal balls of a ball bearing can roll freely. They are designed to make the moving parts of a machine to roll over each other rather than slide. The ball bearing is introduced between the two surfaces which have to rotate over each other. The axle is fixed on the inner side of a ball bearing and wheel is fixed to the outer side of the ball bearing the ball bearing. They reduces friction by making the two surfaces (axle and wheel) to roll over each other. This happens due to the rolling action of small metal balls present inside the ball bearing.
Even a wheel produces some friction where its central hole rubs with the axle. To reduce friction still further, wheels are mounted on ball bearing. The ball bearing is fixed between the hub of wheel and axle. When the wheel revolves the balls of ball bearing roll and reduce friction. The use of ball bearing makes the wheel roll smoothly over the axle. In most of the machine friction is reduced by using ball bearing. The Wheels of the bicycle turn on sets of ball bearing. These ball bearings reduce friction because they roll rather than slide.
Example where sliding friction changes into rolling friction .
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Mrs Shilpi Nagpal says
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