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Force of Friction

Factors affecting friction : -

Let us understand factors affecting friction with this activity.

At the end of this activity students will be able to:

  • Recognize that weight and surface type affect friction. 
  • Recognize that surface area does NOT affect the friction.
  • Recognize that some things are hard to measure like friction because the spring scale needle vibrates.

Materials Needed : -

  • 3 wooden blocks
    • Small screw hooks that can be screwed into the blocks to hook the blocks
    • together.


    spring scale
    Different surfaces like a table, carpet, glass, etc.


    Join the wooden blocks with the help of hooks in the form of a train and suspend it with spring balance.


    Try moving this setup as per the instructions given and answer the following questions. Move a single wooden block on the table and find out the friction with the help of spring balance for the given surface area.



    What happens if you double the weight by stacking one block on top of the other ?


    The frictional force double.


    What happens if you keep the weight the same but double the surface area ?


    The frictional force stays the same.


    What happens if you double the surface area and double the weight ?


    The frictional force is doubled (the increase in weight doubles the force and the surface area has no effect).

    Now try moving this setup on carpet and glass.



    How does the surface type affect the frictional force?


    Friction is caused by the irregularities on the two surfaces in contact .Since irregularities are more on rough surface, the friction is greater. The smoother surface has less friction. However, sometimes glass which is very smooth will produce a large frictional force, specifically if it is very clean. There is a weak vacuum that is formed that pulls the blocks together when there is little or no air between the surfaces. The frictional force is affected by the surface type and weight. It is not affected by the surface area.


    The laws of friction, given below are based on some of these experimental results.

    • The friction force is directly proportional to the normal reaction between the surfaces.
    • The frictional force opposes the motion or its tendency to the motion.
    • The frictional force depends upon the nature of the surfaces in contact.
    • The frictional force is independent of the area.

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