Friction is defined as a force that works in the opposite direction of motion. In other words, friction is a force that opposes motion.
Let us suppose that a book is lying on a table. If we tilt the table slightly, the book will start sliding down the table. However, the motion of the book will gradually slow down, and may even stop. This is because the force of friction opposes the direction of the book’s motion and stops it from sliding down and falling onto the ground.
Frictional force is created between two objects only when they are in contact, and they rub or slide against each other.
Friction is offered by all the three states of matter, but it is most prominently observed between two solids.
Factors That Characterise Friction-
Friction between two objects depends on the following factors-
- Nature of the two surfaces in contact-
Different surfaces display different degrees of friction. Rough surfaces offer a greater degree of fiction, compared to a smooth surface. Rougher a surface, greater will be the strength of the frictional force. Conversely, a smooth surface will offer a low degree of friction. Very low surfaces such as glass offer very less friction.
If both the surfaces that are in contact are rough, then the frictional force will be very large. When one surface is smooth, and the other is rough, then the force of friction will be slightly lower. And if both surfaces are smooth, then the force of friction will be the lowest.
- Weight of the object-
Suppose we want to push an object across the floor. Since weight of a body is the gravitational force acting on the body, a larger gravitational force is exerted on a heavier body by the floor, as compared to a lighter object. Thus, the force of friction is greater when an object being pushed is heavier as compared to when we push a lighter object.
Greater the weight of a body, greater is its frictional force, and lower the weight of a body, lower is its frictional force.
How Friction Helps In Daily Life-
Although friction is a force that opposes motion, it is also the force that makes motion possible. If there was no friction between our feet and the ground, we wouldn’t be able to even stand, much less walk. That is the reason why it is difficult to walk on wet, highly polished, icy or oily surfaces- because there is hardly any friction between our feet and the surface.
Friction is advantageous is other ways too-
- Vehicles are able to move on the road because of the friction between their treaded tyres and the road. They are also able to stop when required, because the brakes exert fiction on the wheels, causing them to slow down and then stop.
- We are able to hold objects in our hands because of the friction between our hands and the object.
- Friction lets us write on paper. It is therefore difficult to write on smooth surfaces such as glass or plastic, because there is negligible friction.
- A matchstick that is rubbed on the side of the matchbox lights up because of the friction between the chemical-laden tip of the matchstick and the matchbox.