Name the force which always opposes motion.

Why does a fast car slow down if its engine is switched off?

Which type of surfaces produce

(a) least friction, and

(b) too much friction?

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

Name a device which is used to measure force acting on an object.

What is a spring balance?

Out of sliding friction, static friction and rolling friction:

(a) which one is the smallest?

(b) which one is the largest?

Which type of friction comes into play when a book kept on cylindrical pencils is moved by pushing?

Why is it more difficult to walk properly on a well-polished floor?

Why is it difficult to walk on a wet marble floor?

Which force is responsible for the wearing out of car tyres?

What prevents you from slipping every time you take a step forward?

Name the force which helps things to move and stop.

What enables us to fix nails in a wall and knots to be tied?

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

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

Why do gymnasts apply a coarse substance to their hands?

Why do kabaddi players rub their hands with dry soil?

Name the device which is used between the hubs and axles of bicycle wheels to reduce friction.

What is the purpose of using ball bearings in machines?

Name any two machines in which ball bearings are used.

Name the device which is attached to heavy luggage (such as a heavy suitcase) to move it easily by pulling.

Name one example from everyday life where wheels (or rollers) are used to reduce friction.

Why does oiling the-axles of a bicycle make the bicycle move more easily?

State one way in which the friction between wheel and its axle can be reduced.

Name two common lubricants.

Why do we sprinkle fine powder on carrom board?

Which force gets reduced when the two surfaces in contact are polished to make them smooth?

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

Name the force which increases when the two surfaces in contact are made more rough.

What is the special name of frictional force exerted by fluids (like air or water)?

What is the name of 'special shape' which is given to objects moving through air (or water) to reduce drag?

Why are grooves provided in the soles of shoes?

Why are treads made in the surface of tyres?

Fill in the following blanks with suitable words :

(a) Friction always opposes..............between the surfaces in contact with each other.

(b) Sliding friction is …………..than the static friction.

(c) Friction produces................

(d) Friction prevents our foot from..............over the ground.

(e) Sprinkling of powder on the carom board.............friction.

(f) Ball bearings reduce friction because they...............rather than 'slide.

(g) The friction when something moves through a liquid or gas is called……

(h) Cars and speedboats are...........to reduce drag.

(i) Shapes that are designed to reduce air resistance are called............shapes.

(j) Objects which can move quickly through the water have a ………shape.

(k) The shape of an aeroplane is similar to that of a............in flight.