# Friction

Friction is a force that tries to oppose motion between the two surfaces in placed contact. When we throw a ball on the floor it starting with some velocity. But once it is rolled ideally no force is acting in the direction of motion and according to Newton’s first law the ball should keep on rolling but this does not happen. The ball stops after moving certain distance, so a force must be acting on it. That force is known as Friction.So, we tend to develop a common definition that frictional force tends to oppose the motion. But that’s not completely true. Consider a block kept on another block. If I apply force on the lower block it begins to move. Along with, it the upper block also starts moving. In this case, it is responsible for the motion of the upper block.

What is friction?

A Friction is a kind of force created by rubbing and can slow things down and then ultimately stop them.

When two objects or bodies are in contact with each other, then a force comes into play. What makes the tires of the car wear away? What makes the Machine parts which come in contact with each other wear away subsequently? What makes the match sticks burn when they are scratched on an unequal surface? What makes us slip on a wet floor?

The answer to all these questions is an imaginary force called Friction which comes into execution when two bodies or objects come in contact. Rough surfaces create more friction than smooth one.

Friction is a force that always exists between two bodies that are in contact with each other.

(Or)

The opposing force of nature or the force which opposes motion of objects or bodies.

(Or)

Friction is the force which basically resists the relative motion of objects, solid surfaces, and even fluid layers sliding over each other.

(Or)

Friction can be defined as a force which is against an object when it touches another object.

(Or)

When an object moves over the surface of another object, its motion is always opposed by a retarding force that resists motion. This retarding force is called friction and it always acts in the direction opposite to the motion of the object.

What Causes Friction?

Friction enables us to walk without slipping and gives the car tires grip on the road surface preventing them from skidding, at the same time, it can also prevent us from moving as fast as we would like to.

Now, let us understand its origin and main cause for it. Take two pieces of sandpaper facing each other. Now bring them in contact and try to rub them against each other, you will find it difficult to move. Why do you think so? The answer is that the irregularities of both the surface get locked with each other and prevent slipping.

The same is the case between two sheets of paper, sheets of glass, even two different material like a wooden plank on a concrete floor, being rubbed against each other. In the case of two cell – Polished surface, interlocking occurs but at a microscopic level.Friction is the retarding force which comes into play when a body actually moves or tends to move over the surface of another body. To move a body we need force. When we move or try to move a body over another body by the aid of a force, the interlocking causes a retarding frictional force which acts in the opposite direction of the applied force.

Friction can also be caused due to molecular adhesion, sticky materials can lead to friction. It can also be caused by deformation. When the materials is soft, it deforms under pressure and hence causes more resistance to motion.

Examples of Friction:

• When we rub our hands together, the heat produced is due to friction.
• Meteors falling, enter into the earth’s atmosphere and burn due to friction.
• Wearing of the tires of vehicles is due to friction.
• We are able to stand on the ground due to the force of friction.
• Lighting a matchstick is possible only because of friction between the stick and the box.
• When we use a rubber to erase what we have written, it is possible only because of the friction.
• When we apply the brakes then friction acts opposite to the engine’s thrust and causes the vehicle to stop.
• The adhesion that the rails have on the tracks is only because of friction between two surfaces.
• It is useful in many engineering disciplines.