Cause of friction

Question 1 Which type of surface produce least friction?

Question 2 Which type of surface produce too much friction?

Question 3 Name a device which is used to measure force acting on an object?

Question 4 What is a spring balance?

Question 5 Which will cause more friction:A rough surface or a smooth surface?Why?

Question 6 What is meant by irregularities of surface?

Question 7 What is the cause of friction?

Question 8 Give example to show that friction depends on the nature of two surface in contact?

Every object has a rough surface, though the surface may appear to be smooth to the naked eyes.When we see through a microscope, it is found that the surface of all the objects have rough edges. Some of the particles on the surface of objects are in the form of tiny hills while other form grooves.The tiny hills or grooves on the surface of object are called irregularities of surfaces.

When we try to move one object over another object, the irregularities present on their surface get entangled or  locked with one another. The interlocking of irregularities of the two surfaces opposes the motion of one object over the other and give rise to force of friction.

Friction is caused by the interlocking of irregularities in the surface of two objects which are in contact with each other. To move one object over the other ,we have to apply a force to overcome interlocking of the irregularities in their surfaces.

More the roughness of a surface larger is the number of irregularities on its surface and has greater will be the friction does the force of friction.The force friction is greater if very rough surfaces are involved.


Let us take two wooden blocks A and B kept one over the other.The rough surfaces of these wooden blocks have lot of irregularities. When we pull the upper wooden block A over the lower wooden block B by applying a force, then the irregularities of their rough surface get entangled or locked with one another.

This interlocking of surfaces gives rise to force of friction which opposes the motion of upper block A over the lower block B. We are able to move block A over block B because we apply sufficient muscular force while pulling to undo the interlocking of surfaces and overcome the opposing frictional force.

The block A moves over block B only when the pulling force applied by us becomes greater than the force of friction holding them together. Friction is small for smooth surfaces.Friction is small for smooth surface.Friction is much greater for rough surfaces.

The spring balance is a device which is used for measuring force acting on an object.The spring balance contains a coiled spring which gets stretched when a force is applied to its free end.The extent by which the spring get stretched is a measure of force applied. Larger the stretching of street spring ,greater will be the magnitude of force applied. The stretching of spring or magnitude of force is indicated by a pointer attached to the spring which moves on graduated scale. The reading on the scale of spring balance gives us the magnitude of force.When the spring balance is held vertically, it is said to measure the weight of an object hung from its hook. And when a spring balance is held horizontally, it can be used to measure the force applied to pull the object on a horizontal surface.

spring balance

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