Substances that reduce friction are called lubricants. Oil, grease, graphite and fine powder are lubricants. The applying of lubricants (such as oil, grease, etc.) to a machine is called lubrication.

Study the following pictures carefully and answer the following questions: On which surface will you experience the highest friction?

Friction depends on the nature of the surfaces in contact. When the two surfaces in contact are smooth, then the friction between them will be small (because the interlocking of smooth surfaces is less). On the other hand, when the two surfaces in contact are very rough, then the friction between them will be very large (because the interlocking of very rough surface is too much). From the given pictures, picture C indicates a stone which have a rough surface than other two. So here the stone surface offers more friction as it is rough.

Study the following pictures carefully and answer the following questions: On which surface will you experience the lowest friction?

Friction is not the same for all the surfaces. When the two surfaces in contact are smooth, then the friction between them will be small (because the interlocking of smooth surfaces is less). On the other hand, when the two surfaces in contact are very rough, then the friction between them will be very large (because the interlocking of very rough surface is too much). From the given pictures, picture A represents a tile which has a smooth surface. So tile will offer least friction as it is having a smooth surface than other two.