Why does a matchstick light when we strike it on a rough surface?
17. What makes the steps of foot over‐bridges at Railway stations to wear out
18. State two advantages & two disadvantages of friction.
19. Why do kabaddi players rub their hands with dry soil?
20. Why are treads made in the surface of tyres?
21. Explain why, oil or grease is applied to those parts of machine which are in
22. What is the special name of frictional force exerted by fluids (like air or water)?
23. What are the factors that affect the fluid friction?