Friction :

1. promotes motion
2. opposes motion
3. acts in the direction of motion
4. is always a nuisance.

Friction is reduced by :

1. making the surfaces wet
2. making the surfaces dry
3. making the surfaces rough
4. sprinkling sand on the surface.

Friction is increased if :

1. an oil is sprayed
2. the surfaces are made wet
3. the surfaces are made dry
4. the surfaces are polished

Fill in the blanks :

(a) Force is applied as …………… or …………… .

(b) On squeezing a gum tube, its …………… changes.

(c) On pulling a string, its …………… increases.

(d) A moving football when kicked, its …………… changes.

(e) On applying brakes on a moving car, its speed …………… .

(f) We use ball bearings to …………… the friction.

(g) Friction …………… motion.

(h) Lubricants are used to …………… friction.

(i) Friction causes …………… of moving parts of a machine.