Friction is a force that tends to oppose the relative motion between two bodies in contact. Frictional force always acts on a moving body from the direction opposite to the direction of motion. It opposes the motion, and therefore, helps to reduce the speed of the moving object. It is a contact force. Based on the type of motion between the two objects, the force of friction can be classified into four broad categories.
Types of Friction
1. Static Friction
A force of friction that acts between an object and a surface on which the object is placed is known as static friction. When a force is applied to an object resting on a surface to put it into motion, the main requirement is that the magnitude of applied force must be higher than the force of friction provided by the surface. It is also known as limiting friction. Walking, rock climbing, etc., are some examples of static friction.
2. Sliding/Kinetic Friction
Sliding friction exists when an object is dragged over the surface of another. It is weaker than static friction. Sliding friction is also known as kinetic or dynamic friction. Dragging a block kept on the table, writing, playing on a slide, etc., are some examples of sliding friction.
3. Rolling Friction
When a body is made to roll over the surface of another body, rolling friction is said to be existing between them. It is much smaller than kinetic friction. Roller skates, ball bearings, etc., are some of the applications where rolling friction can be clearly observed.
4. Fluid Friction
A fluid is a substance that can flow and is able to take the shape of the container in which it is kept. The opposition force presented by a liquid or a gas to the moving object is known as fluid friction. The frictional force presented by the air is called the air resistance force or the drag force. Walking through a pool filled with water and amidst a storm is difficult due to the presence of fluid friction.
Examples of Friction
1. Rubbing Hands
Rubbing hands is an example of sliding friction. When the hands are rubbed against each other, a force opposing this motion of the hands comes into action. The force resisting the motion is applied in the direction opposite to the direction of motion of the hands is called the frictional force and is responsible to generate heat energy.
2. Climbing a Rock
When a climber tends to move on the rock a force is felt in the opposite direction that tries to resist the motion. This force is known as the force of friction. Rock climbing makes use of a force of friction to establish a proper grip between the feet/hand of the climber and the surface of the rock. It helps the climber to climb the rock and prevent his/her hands and feet from slipping.
The surface of a playing slide is made as smooth as possible. This is done because the friction coefficient of smooth surfaces is less than the friction coefficient of rough surfaces. A large friction coefficient allows the person to build a strong grip, whereas a small friction coefficient makes the surface slippery. This lack of grip and friction helps to execute the sliding action on a playing slide. Hence, a person sliding down a slide is one of the best examples to demonstrate friction in real life.
4. Sliding a Sled
A sled sliding over an icy surface is yet another example of kinetic friction. The ice deposited over the ground surface or the land decreases the force of friction between the object and the surface. This lack of friction causes the objects present on the surface to slip and slide easily. This is the reason why people living in such regions wear boots with nails attached to the base. The nails provide a better grip and help the person to walk without slipping.
5. Dragging a Chair
When a small amount of force is applied to a bulky chair, it does not move. This definitely means that a force is being applied from the opposite direction that has a greater magnitude than the external force applied in order to move it. This is known as the force of friction. In order to move the chair, a person has to apply a force that has a magnitude greater than the magnitude of the frictional force.
6. Carrom Board
The striker is susceptible to face a force of friction when it is made to slide over the surface of a carrom board. This force of friction slows down the speed of the striker and sometimes resists its motion. Usually, dusting powder is used to reduce the frictional force and cause the striker to move smoothly.
7. Braking System
A moving vehicle is made to stop by applying a force from the opposite direction that resists the motion. The braking system usually consists of brake pads and rims. Sliding friction existing between the two components helps to slow down the speed of the rolling wheels of the vehicle and cause it to stop. In the absence of friction, an object tends to move continuously with a constant speed.
Walking is possible only due to the presence of a force of friction between the ground and the feet. Friction is a contact force, which means it is present between the point of junction. It helps in establishing a firm grip between the foot and the ground. A proper grip is necessary to move forward. The application of Newton’s third law of motion can also be seen here because the force applied to the ground is equal and opposite to the force of friction produced by the ground.
9. Slippery Floor
While stepping on a slippery or wet floor, it becomes highly difficult to maintain balance. This is because water present on the floor reduces the frictional coefficient. In the absence of the frictional force, an improper grip is formed between the feet and the floor. It may lead to accidents.
10. Rolling Ball Stops Eventually
When an external force is applied to a ball, it comes into motion. The motion-induced in the ball causes it to roll and advance forward. However, after some time, the speed of the ball decreases, and it eventually comes to rest. This change in speed occurs due to the resistance provided by the force of friction, which acts on the ball from the direction opposite to the direction of motion.