Law
State the laws of kinetic friction
Laws of Kinetic Friction are:
1. The force of kinetic friction is independent of the area of contact so long as the normal reaction remains the same.
2. It is independent of the velocity of sliding provided the velocity is neither too small nor too large.
3. It is proportional to normal reaction i.e., , , where is the constant of proportionality and is called the coefficient of kinetic friction so
1. The force of kinetic friction is independent of the area of contact so long as the normal reaction remains the same.
2. It is independent of the velocity of sliding provided the velocity is neither too small nor too large.
3. It is proportional to normal reaction i.e., , , where is the constant of proportionality and is called the coefficient of kinetic friction so
Law
Static friction
A block is kept on a horizontal surface. A horizontal force F is applied. The block dose not move. This is because the applied force balances friction. This frictional force which just balances the applied force is called static friction. It is called so as body is still at rest.
If the applied force is increased, the friction also increases and reaches a maximum. Just before the body starts sliding over the surface of another body, the value of frictional force is maximum and this value is called limiting friction.
If the applied force is increased, the friction also increases and reaches a maximum. Just before the body starts sliding over the surface of another body, the value of frictional force is maximum and this value is called limiting friction.
Example
Rolling Friction
A solid sphere of mass is placed on a rough inclined plane as shown in the figure. The coefficient is insufficient to start pure rolling. The sphere slides a length on the incline from rest and its kinetic energy becomes . Then, the work done by friction will be given by:
Work done by friction + Work done by gravity + work done by normal force = Kinetic energy
(Work energy theorem)
work done by normal force=0
Work done by gravity is mglsin
Work done by friction =
Work done by friction + Work done by gravity + work done by normal force = Kinetic energy
(Work energy theorem)
work done by normal force=0
Work done by gravity is mglsin
Work done by friction =
Definition
Types of Friction
There are 2 types of coefficients of friction.
1. Static
2. Kinetic
The static coefficient of friction is more than or equal to Kinetic coefficient of friction.
1. Static
2. Kinetic
The static coefficient of friction is more than or equal to Kinetic coefficient of friction.
Definition
Fluid Friction
Fluid friction is the resistance to an object's motion through a liquid or gas. When the motion is occurring in a liquid, it is referred to as viscous resistance. As an example, when an object falls through water, its speed reduces due to fluid friction acting on it.
When we add lubricant between two surfaces, fluid friction acts between them. This helps reduce wear and tear between the two surfaces in contact caused due to friction in the absence of lubricant.
When we add lubricant between two surfaces, fluid friction acts between them. This helps reduce wear and tear between the two surfaces in contact caused due to friction in the absence of lubricant.
Definition
Identify factors influencing the fluid friction
The factors affecting fluid friction are:
- Material surface roughness
- Viscosity of fluid
- Length of pipe
- Diameter of Pipe
- Flow Rate of fluid
Example
Friction as a necessary evil
Friction is sometimes essential. A basic example is that friction is necessary for walking. Friction acts between our feet and the ground when we walk. If the ground were perfectly smooth, we would always slip and never be able to move forward. Similarly, friction is necessary for a tire to move on the ground. Also cars, when once in motion would never be able to stop in the absence of friction. When brakes are applied, friction acts on the tires and pulls the car to stop.
Definition
Advantages and Disadvantages of friction
Advantages of friction
1) We are able to walk or run properly on the floor because of friction. If there is less or no friction we will slip and fall down.
2) It would not be possible to light a match stick without friction between its head and the side of the matchbox.
3) Cars and buses are able to run on the roads because of the friction between the wheels and the road.
4) We cannot write on paper without friction between the tip of a pen or a pencil and the paper.Disadvantages of Friction 1. Friction produces heat. This heat causes wear and tear of the machinery parts.
2. Vehicle tyres and soles of footwear wear out because of friction.
1) We are able to walk or run properly on the floor because of friction. If there is less or no friction we will slip and fall down.
2) It would not be possible to light a match stick without friction between its head and the side of the matchbox.
3) Cars and buses are able to run on the roads because of the friction between the wheels and the road.
4) We cannot write on paper without friction between the tip of a pen or a pencil and the paper.Disadvantages of Friction 1. Friction produces heat. This heat causes wear and tear of the machinery parts.
2. Vehicle tyres and soles of footwear wear out because of friction.
Example
Methods to increase or reduce friction
To reduce friction we can make the surfaces in contact smooth. Also adding a lubricant to two surfaces in contact reduces friction between them. Grease is added between the moving parts in machines, to reduce friction. Another method of reducing friction is by using bearings. When ball bearings are introduced between two surfaces friction is reduced because of the freely rotating metal balls.
To increase friction, the surfaces in contact have to be made rough. The two surfaces in contact can also be pressed harder to increase force between them. Use of adhesive materials that stick surfaces , also increases friction between them.
To increase friction, the surfaces in contact have to be made rough. The two surfaces in contact can also be pressed harder to increase force between them. Use of adhesive materials that stick surfaces , also increases friction between them.
Definition
Coefficient of static friction
Coefficient of static friction is a property of pair of surfaces. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one.
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