Science Question Answer (3 Marks)

A very heavy machine can be moved from one place to another with the help of wheels. Because then rolling friction comes into action and its value is the least among static and sliding friction.
The following diagram shows, how a heavy cylinder can be rolled easily.

Lubricants (oil or grease) are applied to rubbing surfaces of machines because when the parts rub against each other, heat is produced. To avoid the wearing and tearing of the machine parts, lubrication is done. Because it reduces the friction and thus less heat is produced.

Seema will have to apply larger force than Iqbal.
Because Seema’s box is heavier and Seema will have to apply greater force to overcome the larger friction in case of the heavier box.

A speedboat has a streamlined shape so as to reduce the fluid friction as it moves in the waters.

When step forward and walk, we are applying force (denoted by “F”) on the ground. Now, in return ground also applies the reaction force to us. But we can fall if friction (denoted by “f”) is not present as the large ground can apply a large force. This is explained in the diagram:

A streamline shape is the one in which the body is pointed at the ends and broad-shaped in the middle.

Example:
Speedboat has streamlined shape.

Whenever we push a very heavy box kept on the ground, it does not move at all because frictional force balances the force that we apply. So, there is no net movement of this box. It acts in a direction opposite to the force we apply.