Use the molecular theory of matter to explain the laws friction s

1. State the laws of static friction. (03 marks)

• Friction force opposes relative motion between surfaces in contact.
• Friction force is independent of area of contact provided normal reaction is constant.
• The friction force is directly proportional to the normal reaction.

(ii) Use the molecular theory of matter to explain the laws friction stated in (a)(i) (06 marks)

• On a microscopic level, even seemingly smooth surfaces have rough and uneven features (high and low points). When two surfaces come into contact, the high points (asperities) of one surface are welded to those of the other with strong attractions.
• Actual area of contact between solid surfaces is very small. Therefore pressure at points of contact is very high; projections emerge to produce adhesion or welding. Motion in any direction has to break the attractive force at the point of contact i.e. force which oppose motion is obtained (Law I)
• The actual area of contact is the sum of the areas of tiny projections that adhere to each other and are nearly independent of the surface areas of contact.(law II)
• Increase in weight increases the actual area of contact and hence greater limiting frictional force.(Law III)
• Also, the movement of surfaces over each other results in the conversion of kinetic energy into other forms of energy, such as heat. This energy dissipation is a fundamental aspect of friction, as it opposes the relative motion of the surfaces. (Law I)

Dr. Bbosa Science