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Friction Experiment Viva Questions


Coefficient of Friction Experiment Viva Questions and Answers


1. What is meant by friction?


Friction is an opposing force that comes into effect when a body moves or even tries to moves over another body’s surface.


2. Name the different types of friction.


(i). Static friction, (ii) limiting friction and (iii) kinetic friction


3. Define static friction.


Static Friction is the opposing force that comes into effect when one body tends to move over the surface of another, when they are not in motion with respect to each other.


4. Define limiting friction.


Limiting friction is the maximum value of the frictional force that comes into effect when a body just starts to slide over another body’s surface.


5. Define kinetic friction.


Kinetic friction is the frictional force that comes into effect when a body is in a steady state of motion over the surface of another body.


6. Name two types of kinetic friction.


i. Sliding friction ii. Rolling friction


7. Define coefficient of limiting friction (µ).


Coefficient of limiting friction is defined as, the force of limiting friction is directly proportional to the normal reaction force between them.

F R, F = µR


6. Is friction a self adjusting force?


No. Only static friction is a self adjusting force.


9. Why are wheels circular?


Because rolling friction is less than sliding friction.


10. Distinguish between static friction and dynamic friction.


The static friction is defined as the frictional force acting on a body when at rest. And the kinetic friction is defined as the force of friction acting on a body when in a relative motion.


11. What are the factors on which coefficient of friction depends?


The coefficient of friction depends on the

(i) nature of the surface in contact

(ii) material of the surfaces


12. What is rolling friction?


It is the frictional force that resists the motion of a rolling body on a surface.

Eg: car's wheels on the ground


13. Why is friction considered a necessary evil?


Friction is useful as well as harmful. It is necessary, because it helps us on walking, writing, holding things, lifting the objects. So it is necessary in our lives. Also frictional force causes a lot of losses in general. It causes most of the injuries when we fall down. It also results in loss of energy, wear and tear of machinery. So it is considered a necessary evil.


14. Lubricants reduces friction, how?


When a lubricant is added between two surfaces rubbing each other, it fills the irregularities present on the surfaces and smoothes the process by forming a film between the two rubbing surfaces which reduces the friction. Thereby the performance and efficiency would be increased.


15. Aim of Friction Experiment


i. To determine the relation between force of limiting friction and normal reaction force.

ii. To find the coefficient of friction between a block and a horizontal surface.


16. Apparatus of Friction Experiment


A wooden block, a set of 50 gram weights, a weight-box, pan, a horizontal table fitted with a frictionless pulley, spring balance, spirit level etc.


17. Principle of Friction Experiment


F R --------------- (1)

F - Force of limiting friction

R -Normal reaction

Coefficient of friction, µ = F/R ----------- (2)


18. Procedure of Friction Experiment

The weights of the given wooden block and the pan are first taken using a spring balance. The wooden block is then placed on a horizontal table and its horizontability is checked with the help of a spirit level. A thread is tied to the hook of the block and is passed over a pulley. The weighed pan is attached at the free end of the thread.


With no weight over the block, weights are added on the pan in steps till the block just begins to slide on tapping the table. The weights in the pan are noted. Now a 50 gram weight is placed over the block and additional weights are added on the pan till the block again just begins to slide. The experiment is repeated by placing different weights over the block.


It is seen that the force of limiting friction, F is directly proportional to the normal reaction, R. The coefficient of friction, µ is found out using relation (2).


A graph is plotted with normal reaction, R, along the X-axis and force of limiting friction, F, along the Y-axis. The graph is a straight line. The slope of the graph gives the coefficient of friction, µ , between the block and the horizontal surface.

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