Friction

Q1. Fill in the blanks.

                         i.        Friction opposes the motion between the surfaces in contact with each other.

                        ii.        Friction depends on the nature of surfaces.

                       iii.        Friction produces heat.

                       iv.        Sprinkling of powder on the carrom board reduces friction.

                        v.        Sliding friction is less than the static friction.

Q2. True/False

                         i.        The force of friction always opposes the applied force. True

                        ii.        On rough surfaces, there are a lesser number of irregularities. False

                       iii.        Sliding friction is slightly smaller than the static friction. True

                      iv.        Friction is caused by the irregularities on the two surfaces in contact. True

                       v.        Soles of shoes wear out due to gravity. False

Q3. Which force helps things to move and stop?

Ans. Frictional force

Q4. What enables a ladder to lean against the wall?

Ans. Friction

Q5. Name two common lubricants.

Ans. Oil and Grease

Q6. Mention one simple method of reducing friction between two surfaces.

Ans. Lubrication

Q7. What is drag?

Ans. The frictional force exerted by fluids is also called drag.

Q8. Which type of surface produces less friction?

Ans. Smooth surface produces less friction.

Q9. Why the soles of our shoes wear out gradually?

Ans. The soles of shoes wear out gradually due to friction.

Q10. Which type of surface produces more friction?

Ans. Rough surface produces more friction.

Q11. Why ball bearings are used in machines?
Or
What is the purpose of using ball bearing in machine?

Ans. Ball bearings reduce friction. Thus, they are used in machines.

Q12. Write any two machines in which ball bearings are used.

Ans. Ceiling fans and Bicycles

Q13. What makes the steps of foot over-bridges at Railway Stations to wear out slowly?

Ans. Frictional force

Q14. What are lubricants?

Ans. The substances which reduce friction are called lubricants.

Q15. Why do we sprinkle fine powder on the carrom board?

Ans. Powder is sprinkled on the carrom board to reduce friction.

Q16. Name the force responsible for wearing out of car tyres.

Ans. Frictional force is responsible the wearing of car tyres.

Q17. What is the direction of force of friction acting on a moving object?
Or
What is the direction of force of friction?

Ans. The force of friction always opposes the applied force.

Q18. Which force always opposes motion?
Or
What is the force that always opposes motion?

Ans. Friction force always opposes motion.

Q19. What is done to increase friction between the tyres and road?

Ans. The tyres of the vehicle are treaded to increase friction.

Q20. When does static friction come into play?

Ans. Static friction comes into play when we try to move an object at rest.

Q21. When does sliding friction come into play?

Ans. Sliding friction comes into play when an object is sliding over another.

Q22. Why is the surface of a slide polished to make it smooth?

Ans. The surface of a slide polished to make it smooth in order to reduce friction.

Q23. Why do kabaddi players rub their hands with dry soil?

Ans. Kabaddi players rub their hands with soil for a better grip of their opponents.