Laws of Friction

Friction

The force exerted by two surfaces sliding (or attempting to glide) across one another is known as friction. For instance, friction makes it more difficult to push a book across the floor. Whenever an object moves or attempts to move, the friction acts in the opposite direction. Friction always tries to slow down a moving thing. 

The materials used to construct the two surfaces determine the degree of friction. When the surface is rougher, the friction increases. Friction also produces heat. If you rub your hands together quickly, you will notice that they become warmer. In our shoes, friction prevents them from slipping on the pavement, and in cars, friction prevents the wheels from skidding as we walk. The tread of your shoes grinds against the ground when you walk, generating friction. This friction protects you from sliding by gripping the ground.

There are times when we all want to reduce friction. We use oil, for example, to minimise the friction between the moving elements inside an automobile engine. It prevents friction between the surfaces and allows fluid to flow between them. As a result, the car’s moving parts wear less and emit less heat as the friction is less.

Types of Friction

Friction can be static or kinetic. When two surfaces are not moving relative to one another, they experience static friction, whereas relatively moving objects encounter kinetic friction. 

Friction, often known as viscosity, is the resistance between moving layers of  fluid in liquids. Fluid friction is higher in honey than in water because viscous fluids are thicker. A solid material can also undergo friction within its atoms. For example, when a solid block of metal is crushed, all the atoms inside the material move, causing internal friction. There are no frictionless settings in nature. Even in deep space, microscopic particles of matter can interact and cause friction.

Coefficient of Friction

When two solid objects move against each other, kinetic friction occurs. In this instance, friction is a percentage of the perpendicular force operating between two objects (the fraction is determined by a coefficient called the coefficient of friction, which is determined through experiments). The force is unaffected by the contact area and the speed at which the two objects travel in general. 

Friction can also be found in stationery things. Static friction prevents objects from moving and is frequently stronger than the frictional force experienced when two objects move in relation to one other. A box cannot slide to the bottom of an incline due to static friction.

Applications of Friction

Many everyday processes are impacted by friction. Friction converts some of the energy of the motion into heat when two things rub together. For example, a fire starts when two sticks are rubbed against each other. Bicycle gears and other mechanical components deteriorate due to friction as well. To reduce friction as well as wear and tear between the moving parts, lubricants or liquids are frequently used.

Laws of Friction

The five laws of friction are as follows:

1. The frictional force acting on the moving object is perpendicular and proportional to the normal force.
2. The qualities of the surface with which the object comes into touch determine the object’s friction.
3. As long as there is friction, it exists regardless of the area of contact.
4. Kinetic friction is unaffected by velocity.
5. Static friction coefficients are generally larger than kinetic friction coefficients.

Static Friction

When the tendency of relative motion exists in the bodies in contact and they are at relative rest, static friction occurs between non-moving solid surfaces. The symbol for static friction is “fs.” 

Static friction does not exist by itself. It opposes the impending motion, implying that it always occurs in the presence of the applied force. There is no static friction if there is no applied force. It has a changeable and self-adjusting value. It does not have a formula because the value is variable. Limiting friction, abbreviated as “Flimiting,” is the maximum value of static friction.

Laws of static friction

The laws of static friction are as follows:

1. The maximum magnitude 

The static friction force is independent of the contact area between two surfaces.

2. Since the magnitude of maximum force is always proportional to the normal force, as the normal force increases, so does the maximum external force that the object can withstand without moving.

Limiting Friction

It is the maximum force of static friction, which is attained when a body is just about to start moving over the surface of another body when they are in touch.

Laws of limiting friction

The four laws of limiting friction are as follows:

1. The normal reaction is directly proportional to the force of limiting friction between two objects: F ∝ N. As a result, if a body is heavy, the usual reaction, i.e., the mg, increases, resulting in greater force being required to move the heavy body than a lighter body.

2. The direction in which one object is about to move over another is always the opposite of the direction in which friction force acts.

3. The force of limiting friction is independent of the area common between the two bodies in contact.

4. The type of substance, as well as the roughness and smoothness, play a role in limiting the friction’s force between any two items in contact.

Kinetic Friction 

Kinetic friction occurs when two moving surfaces collide or when motion is present. The actual motion begins when the applied force is somewhat greater than the limiting friction. Kinetic friction describes the force of friction at this point. Its value is constant and independent of relative motion and contact area. It is denoted by “Fk.” The kinetic friction Fk is proportional to N (normal reaction).

Laws of kinetic friction

The laws of kinetic friction are as follows:

1. Kinetic friction opposes relative motion at all times and has a constant value. The nature of the two surfaces of the items in contact determines its value.

2. The value of kinetic friction Fk is independent of the contact area.

3. Kinetic friction is not completely determined by velocity.

Conclusion 

 We have discussed in detail about friction, laws governing friction. We have also studied about kinetic and static friction and the difference between them and also about the laws governing them separately. We have also covered limiting friction, which comes under static friction.