This question on the laws of solid friction was very popular among the candidates. It was well attempted by most responding candidates. Under observation, candidates missed the unit of R which is Newton (N) as they recorded it in grammes(g)
Plotting of the graph and determination of slope were however well handled by most candidates. The precautions were not properly stated by most candidates. In the part b, most candidates were unable to define correctly the coefficient of static friction but they were able to use formular to calculate the co-efficient of static friction between two surfaces.
The demands of part (a) include the following:
- measurement of and recording of mo, M and F
- evaluation of M = (mo + M) and R =
- data should be recorded in composite table and in trend
(Trend: As m increases, F increases)
- The graph axes should be indictated and reasonable scales selected to plot four
points required;
- determination of the slope using large right angled triangle on the graph line.
- state any two of the following precautions in acceptable speech:
- Avoided parallax error in reading spring balance
- Tapped the wood/load slightly to avoid sticking to the table
- Repeated readings shown on table.
(b)(i) Definition of the term coefficient of static friction
This is the ratio of the frictional force F (when the body is just about to move) to the normal reaction R (Between the two surfaces in contact).
(ii) U= F/R
= 2.5/5
= 0.5
