Solution:
Frictional forces , such as the traction needed to walk without slipping, may be beneficial, but they also present a great measure of opposition to the motion.
About 20 per cent of the engine power of automobiles is consumed in overcoming frictional forces in the moving parts.
The amount of friction is nearly independent of the area of contact.
Friction is proportional to the load or weight that presses the surfaces together.
The ratio of friction F to load L is constant.
This constant ratio is called the coefficient of friction and is usually symbolized by the Greek letter mu(μ) .
Mathematically, μ = F/L.
Static friction , in contrast, acts between surfaces at rest with respect to each other.
When there is no force applied there is no static friction.
It comes into play the moment there is an applied force .
As the applied force F increases, fs also increases , remaining equal and opposite to the applied force (up to a certain limit) , keeping the body atrest. Hence, it is called static friction .
Static friction opposes impending motion.
Hence, Statement 1 is incorrect.
The term impending motion means motion that would take place (but does not actually take place ) under the applied force if friction were absent.
Rolling friction occurs when a wheel, ball, or cylinder rolls freely over a surface, as in ball and roller bearings.
Friction , by definition, is the component of the contact force parallel to the surfaces in contact, which opposes impending or actual relative motion between the two surfaces.
Hence, Statement 2 is correct.
Note that it is not motion, but the relative motion that the frictional force opposes.
In this ideal situation, kinetic or static friction is zero and the body should continue to roll with constant velocity.
In many situations, like in a machine with different moving parts, friction does have a negative role .
It opposes the relative motion and thereby dissipates power in the form of heat, etc.
Lubricants are a way of reducing kinetic friction in a machine.
Another way is to use ball bearings between two moving parts of a machine.
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