Physics
Write true or false for each statement :
(a) The frictional force acts in the direction of motion of body.
(b) The unit of weight is kilogram.
(c) A force can change the direction of motion of a moving body.
(d) A force increases the mass of the body when applied on it.
(e) The force of friction is always disadvantageous.
(f) The sliding friction is more than the rolling friction.
(g) Liquids offer more friction than the gases.
(h) A wet oily road offers more friction than a dry rough road.
Force
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Answer
(a) False because friction is the force that opposes the relative motion between the two surfaces in contact with each other.
(b) False since weight, being a force, is expressed in gravitational unit kgf or gf whereas kg or g is the unit of mass.
(c) True as if a force is applied on a moving body in a direction other than its direction of motion, the direction of motion of the body changes.
(d) False because a force does not change the mass of the body on which it is applied.
(e) False as friction is advantageous to us in almost all activities of our life, for example it helps us in walking or rotating a wheel etc.
(f) True since static friction > sliding friction > rolling friction
(g) True as gases offer less friction than liquids, while liquids offer less friction than solids.
(h) False because a dry rough road offers more friction than a wet oily road due to large numbers of pores or depressions in the dry road as compared to wet oily road.
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Related Questions
Friction is increased if :
- an oil is sprayed
- the surfaces are made wet
- the surfaces are made dry
- 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.
Match the following columns :
Column A Column B (a) Non contact force (i) repel (b) Like poles (ii) kg (c) Contact force (iii) Gravitational force (d) Mass (iv) wear and tear (e) Weight (v) force of friction (f) Friction (vi) kgf Name the term used for the push or pull.