Answer the following questions in short
a)Why is sliding friction slightly less than static friction?
b)What do you mean by adhesive force?
Answer the following question in detail-
Friction is a necessary evil.Justify the statement.
Answers
Answer:
For a given two surface, sliding friction is slightly lesser than that of the static friction because it is easy to move the object which already in motion than the object which is at rest.
Attractive forces between molecules of different types are called adhesive forces. Cohesive forces between molecules cause the surface of a liquid to contract to the smallest possible surface area.
Frictional force causes a lot of losses in general upkeep and wear and tear of machinery. ... But almost all crucial tasks cannot be carried out without the presence of friction. Basic activities like walking and writing on a surface are possible due to friction. Hence it is considered as a necessary evil .
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The friction between the two surfaces is because of the interlocking of the irregularities of the two surfaces.
a) During sliding, contact points do not get enough time to get interlocked properly. Therefore, less friction. But, when the object is at rest, the surfaces interlock well, therefore friction is more. This explains why sliding friction is less than static friction.
b) Similarly, the term "adhesive forces" refers to the attractive forces between unlike substance, such as mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges). In the case of a liquid wetting agent, adhesion causes the liquid to cling to the surface on which it rests.
c) friction is said to be a necessary evil because it is useful as well as harmful. friction helps us to walk, write, hold things, lift objects. ... Without friction many essential processes can not be done. On the other hand, it is also unecessary at times.