Suppose your writing table (or desk) is tilted a little. A book kept on the table starts sliding down. Draw a diagram to show the direction of force of friction acting on the book.

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.

When we try to push a very heavy box kept on ground, it does not move at all. Which force is preventing this box to move forward? Where does this force act?

Which will cause more friction: a rough surface or a smooth surface? Why?

Explain why sliding friction is less than static friction.