CBSE Physics Experiment Friction

Introduction

Friction plays an important role in our daily activities such as walking, writing, skating, driving a vehicle on a surface, lighting a matchstick and much more. Without friction, nothing is possible. In this class 11 friction experiment, we'll talk about types of friction, laws of limiting friction, the origin of friction, and the importance and application of friction.

Table of Content

• Aim

• Theory

• Laws of limiting friction

• Conclusion

Aim

Friction

Theory

The resistance provided by surfaces in touch as they move past one another is referred to as friction.

Types of Friction

1. Static Friction

The frictional force that exists between surfaces while they are at rest in relation to one another is known as static friction. When a tiny amount of force is applied, the static force's magnitude is similar in the other direction. 

The examples of static friction are as follows:

• Skiers battling the snow

• Rubbing two hands together to produce heat

Coefficient of Static Friction

The symbol for the static friction coefficient is µs. The product of the coefficient of static friction and normal force is used to calculate the maximum amount of static friction, and the amount of static friction is either less than or equal to this value. It is specified as 

$F_s$ (max) = µs η and Fs ≤ µs η

Where

Fs is the force of static friction

µs is the coefficient of static friction

η is the normal force

$F_s$ max is the maximum static friction force.

2. Sliding Friction

The resistance that is formed between any two items when they are sliding against one another is known as sliding friction.

Some examples of sliding friction:

• The brick is sliding across the floor.

• Two cards in a deck are rubbing against one another.

Coefficient of Sliding Friction

The symbol for the sliding friction coefficient is µs. The sum of the normal force and the coefficient of sliding friction is known as the force of sliding friction. It is specified as

Fs = µs. Fn

3. Rolling Friction

The weakest type of friction, rolling friction is described as the force that opposes a ball's or wheel's motion.

• The instances of rolling friction are as follows:

• The wood rolling on the ground

• The moving vehicles' wheels

Coefficient of Rolling Friction

The symbol for the rolling friction coefficient is r. The sum of the normal force and the rolling friction coefficient is known as the rolling friction force. It is specified as

Fs = µr. Fn

4. Fluid friction

The friction that develops between fluid layers as they move in relation to one another is known as fluid friction.

The instances of fluid friction are as follows:

• The way ink flows out of pens

• Swimming

Origin of Friction

1. The roughness of surfaces causes friction. When two surfaces are moving relative to one another, the roughness or imperfections of the surfaces allow for interlocking. Elevations and depressions on the bodies' lower surfaces and bottom surfaces interlock.

2. Molecules on the body's lower and bottom surfaces are attracted to one another by force. The term for it is sticky force.

Laws of Limiting Friction

There are four laws of limiting friction:

1. Law of Direction: Reducing friction acts in a direction tangential to the surfaces in contact (i.e., opposite to the direction of motion).

2. Law of Magnitude: Limiting friction has a magnitude that is directly proportionate to the normal response that is exerting pressure on the body.

3. Law of Dependence: The law of dependency states that friction can be reduced by altering the type (rough or polished) and material (hard or soft) of the surfaces in contact.

4. Law of Independence: Friction can be reduced regardless of the size and shape of the surfaces coming into contact.

Coefficient of friction

The normal reaction has a direct relationship with the limiting friction.

μ =F/R

F=μ R  

Here F is the limiting friction, R is the normal reaction and μ is called the coefficient of friction. 

Importance of Friction

1. In daily life, friction is vital. Many acts might not be able to be performed without them.

2. A motion cannot begin without friction. On a surface with no friction, we cannot walk.

3. If there is no friction, the brakes will not function.

4. A motion cannot be conveyed without friction. If there is no friction between the belt and the wheels, the belt will not be able to rotate the machine wheels one by one.

5. Knots won't remain if there is no friction. It will be challenging to pack, tie, and bandage.

6. The process of grinding cannot occur without friction. Spices and wheat won't be ground.

7. Nails won't stay in place if there is no friction. A piece of furniture will be challenging to put together.

Application of Friction

1. When matchsticks are lit, it is possible because of friction.

2. Friction is used when pistons move inside a cylinder.

3. Due to the friction between the board and the pen, writing on both books and boards is feasible.

Disadvantages of Friction

Although friction has various applications, it is bad in the following situations.

1. The wear and tear of parts and excessive heat are caused by friction between the various machine parts. The machine's life is shortened as a result.

2. Unnecessary energy expenditure to remove friction As a result, the output is never more than the input.

Ways to Reduce Friction

The following techniques can be used to minimise friction:

1. Polishing and rubbing the surface to make it smoother. Elevations lose height when rubbed. Deeper depressions are filled with polishing. Interlocking decreases in the absence of peaks and valleys. As a result, friction is reduced.

2. However, friction is increased when surfaces in contact are excessively smooth. The molecules on the two surfaces are in close touch, which is why the friction rises as a result of the molecules' increasing attraction to one another.

3. Using the right lubricant to lubricate the surfaces that are in contact. Two surfaces are kept apart and from locking together by a lubricant. It lessens friction.

4. Grease should be used for heavy bodies, heavy oil should be used for bodies of moderate weight, and light oil should be used for light bodies when choosing a lubricant.

5. Adding a soft material layer to the surfaces or surface. Strong molecular tensions between the surfaces of hard materials cause higher friction. They are lined (coated) with soft material to decrease friction between them without compromising their strength. Less friction is created when soft material surfaces come into contact.

6. Converting the friction of rolling into that of sliding friction.

7. By modifying the form of a body travelling through the air, friction due to air can be minimised in jets, planes, swiftly moving automobiles, etc.

Ways to Increase Friction

Several methods can increase friction:

1. Chiselling the surface in order to make it rough.

2. Sanding the outside.

3. Strong material lining.

4. Creating slide friction by converting rolling friction.

Lab Manual Questions

1. What do you understand by the self-adjusting nature of the force of friction?

Ans. As static friction wants the objects to stay at rest and not move, it is seen as a self-adjusting force. Because of this, if an external force is applied, the static friction force will match it until it exceeds the threshold of motion.

2. Why don't we study the limiting friction between the two surfaces using a spherical body?

Ans. The best shape for reducing friction is a sphere since only a small portion of a spherical object comes into contact with the opposing surface. This is the reason why a spherical body was not selected to explore limiting friction between the two surfaces since there is only one point of contact between the body and the plane at any given instant, and this point has no motion connected to the plane.

3. Why is there no possibility of zero friction?

Ans. Since there will always be some friction on every surface, it is impossible to completely eliminate it. A surface cannot have a zero-friction surface, hence a frictionless surface is not feasible.

4. Why are unpolished surfaces typically preferred in experiments related to friction?

Ans. Lessening the area of contact between imperfections on surfaces results in less friction, which reduces the likelihood that the force may have an adverse effect and improves the accuracy of the outcome.

Viva Questions

1. What is the angle of friction?

Ans. The angle of friction is the result of a normal reaction and limiting friction with the normal reaction. The static friction coefficient is equal to the tangent of the friction angle.

3. What is Limiting Friction?

Ans. Limiting friction is the highest amount of static friction that is present when a body is about to slide over the surface of another body.

4. Which is easier: rolling or sliding?

Ans. It is simpler to roll a body along a surface than it is to slide (drag) it because rolling friction is smaller than sliding friction.

5. Is Zero friction possible?

Ans. Although theoretically friction acting on a surface may be zero, this is never practical. It can be drastically reduced, but it can never be zero because of contamination and wear.

6. What kind of friction is not moving?

Ans. While sliding friction happens when objects glide against one another, static friction happens when objects are still. Rolling friction and fluid friction are other types of friction. A surface cannot be moved by an item due to static friction.

7. Does ice have friction?

Ans. Most experts agree that ice's low friction is caused by a thin layer of liquid water that covers its surface. Therefore, skaters on delicate metal blades can glide across the ice rink without incident but come to a grinding halt when they reach the wooden floor beyond.

8. How does friction affect speed?

Ans. Friction always resists motion and reduces the speed of an object moving across a surface. Transforming a portion of an object's kinetic energy into thermal energy will slow it down.

9. Is a higher or lower friction angle preferable?

Ans. Friction angle is the physical representation of particle interlocking. The friction angle should be higher the more tightly the particles lock together, and vice versa.

10. What is the angle of response?

Ans. The angle of repose is formed by an inclined plane and the horizontal when a body is placed on it, and it simply begins to slide.

11. Why is friction less on snow?

Ans. A thin lubricating water layer produced while skiing can be used to explain the low sliding friction between skis and snow. For sliding to take place, this skinny water film is necessary. The snow's free water content creates the water film.

Practical Based Question

1. The force of friction 

1. Always act in the direction of motion

2. Always act against the direction of motion

3. Has no particular direction

4. has a direction based on the size of the body

Ans. The force of friction always acts against the direction of motion.

2. If no force is applied to the moving object, it will stop due to

1. Tension

2. Momentum

3. Impulse

4. Friction

Ans.  If no force is applied to the moving object, it will stop due to friction.

3. If two rough surfaces are polished and put in contact, the friction force will?

1. Increase

2. Decrease

3. Remain constant

4. Either increase or decrease

Ans. If two rough surfaces are polished and in contact, the friction force between them will decrease.

4. Which of the following forces is contact force?

1. Force of gravity

2. Magnetic force

3. Force of friction

4. Electrostatic force

Ans. The Force of friction is the contact force.

5. Which of the following is the wrong example of friction?

1. Sledge sliding across the snow.

2. A person sliding down a slide.

3. A person lifting a heavy object.

4. Washing machine pushed along a floor.

Ans. A person lifting a heavy object is the wrong example of friction.

6. Which of the following produces the least friction?

1. Sliding friction

2. Rolling friction

3. Composite friction

4. Static friction

Ans. Rolling friction produces the least friction.

7. The unit of coefficient of friction in the SI unit of the system is?

1. N

2. Unit less

3. N/M

Ans. The unit of coefficient of friction in the SI unit of the system is unit less.

8. Which of the following cannot be charged by friction?

1. A copper rod

2. A glass rod

3. A plastic pen

4. An inflated balloon

Ans. Frictional charging is not possible with copper rods.

9. The static coefficient of friction is greater than the kinetic coefficient of friction.

1. True

2. False

Ans. The static coefficient of friction is greater when the static frictional force is divided by the kinetic frictional force because the static frictional force is greater than the kinetic frictional force.

10. Limiting friction of a body depends on _____

1. Area of contact of surfaces

2. The volume of the smaller body on a larger surface

3. Nature of surfaces

4. The periphery of the contact surfaces

Ans. Limiting friction only depends on the surfaces' coefficients of friction, or the smoothness or roughness of the surface, because it depends on more than anything else.

Conclusion

Through this experiment, we discovered the significance of friction in daily motion. Without friction, no one in motion will be able to stop, since friction is a force that resists motion. We came to know the types of friction, laws of limiting friction and much more. Also, the importance and application of friction.