- Friction is a
(a) non-contact force
(b) contact force
(c) magnetic force
(d) electrostatic force - The force of friction acts in a direction to the direction of motion of the object. (a) same (b) opposite (c) perpendicular (d) downwards
- Which of the following is responsible for wearing out of bicycle tyres? (a) Muscular force (b) Magnetic force (c) Frictional force (d) Electrostatic force
- Force of friction depends on (a) roughness of surface (b) smoothness of surface (c) Mass of object (d) all of these
- If we apply oil on door hinges, the friction will (a) increase (b) decrease (c) disappear altogether (d) will remain unchanged
- Which of the following is not a smooth surface? (a) Surface of wet soap (b) Surface of tyres (c) Glazed tiles (d) Surface of mirror
- Friction is (a) foe (b) friend (c) both (a) and (b) (d) none of these
- Friction can be reduced by using (a) oil (b) grease (c) powder (d) all of these
- Which of the following produces least friction? (a) Sliding friction (b) Rolling friction (c) Composite friction (d) Static friction
- Friction always
(a) opposes the motion
(b) helps the motion
(c) both (a) and (b)
(d) none of these
Important Questions & Answers of The Chapter
- Fill in the blanks.
(a) Friction opposes the ______ between the surfaces in contact with each other.
(b) Friction depends on the __ of surfaces.
(c) Friction produces ______
(d) The sprinkling of powder on the carrom board _______ friction.
(e) Sliding friction is _______ than the static friction.
Solution:
(a) relative motion
(b) smoothness (or irregularities or nature)
(c) heat
(d) reduces
(e) less - Explain why sportsmen use shoes with spikes.
- Define friction. What is meant by sliding friction ?
- What is meant by lubrication ? Why do we lubricate the moving parts of our vehicles ? Name some lubricants and where they are used.
Answer- Lubrication means oiling the machines from time to time. Lubrication of the moving parts is done to reduce friction between them. We can use oil or grease in machines. Graphite can be used in machines which reach a very high temperature.
5. Yash has to push a lighter box and Rudransh has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
6. Give examples to show that friction is both a friend and a foe.
Friction as a friend:
- It allows us to grip and catch any object.
- It helps us to walk comfortably on the floor.
- It helps to minimise the speed or to stop any moving object.
- It helps us to write.
Friction as a foe:
- It causes wear and tears in objects.
- It causes damage to the parts of machines and tools which further require money to get them repaired.
- It reduces the speed of moving objects, so more force is required.
- It produces hurdles in moving any object freely.