A physicist is investigating the effect that different conditions have on the force of friction. The material used is an ordinary brick, with a mass of 1.8 kg. It is pulled across the surface of a wooden table. Friction is measured by pulling the brick with a string attached to a spring scale, calibrated in newtons (N). When the brick is pulled at constant speed, the reading on the scale is equal to the force of friction between the brick and the table top.
Experiment 1: The brick is placed on the table in three different positions. First, it is allowed to rest on its broad face (area =180 cm2), then on its side (area =130 cm2), and finally on its end (area =56 cm2)
Table 1
Area (cm2)18013056Friction (N)7.17.37.2
Experiment 2: A wooden block of mass 0.6 kg is made to the same dimensions as the brick, and the experiment is repeated.
Table 2
Area (cm2)18013056Friction (N)1.21.11.2
Experiment 3: The time, the wooden block is loaded by adding 1.2 kg of extra mass on top of it, to give it the same weight as the brick.
Table 3
Area (cm2)18013056Friction (N)3.53.63.7
From Experiment 1, it would be reasonable to hypothesize that:
A physicist is investigating the effect that different conditions have on the force of friction. The material used is an ordinary brick, with a mass of 1.8 kg. It is pulled across the surface of a wooden table. Friction is measured by pulling the brick with a string attached to a spring scale, calibrated in newtons (N). When the brick is pulled at constant speed, the reading on the scale is equal to the force of friction between the brick and the table top.
Experiment 1: The brick is placed on the table in three different positions. First, it is allowed to rest on its broad face (area =180 cm2), then on its side (area =130 cm2), and finally on its end (area =56 cm2)
Table 1
Area (cm2)18013056Friction (N)7.17.37.2
Experiment 2: A wooden block of mass 0.6 kg is made to the same dimensions as the brick, and the experiment is repeated.
Table 2
Area (cm2)18013056Friction (N)1.21.11.2
Experiment 3: The time, the wooden block is loaded by adding 1.2 kg of extra mass on top of it, to give it the same weight as the brick.
Table 3
Area (cm2)18013056Friction (N)3.53.63.7
From Experiment 1, it would be reasonable to hypothesize that:
The correct option is A The surface are of contact does not affect the amount of friction x
In spite of the fact that one surface is almost three times as great as another, there is no substantial difference in the amount of friction. The small differences are surely due to experimental variation. This is obvious when it is noted that the value obtained for the 130−cm2 surface is a little larger than that for the 180−cm2 surface. (2) is wrong because there is no comparison with other readings to decide what constitutes large friction. (3) is wrong because the experiment did not vary weight distribution. (4) is wrong because the same object was used throughout.
The surface are of contact does not affect the amount of friction x
In spite of the fact that one surface is almost three times as great as another, there is no substantial difference in the amount of friction. The small differences are surely due to experimental variation. This is obvious when it is noted that the value obtained for the 130−cm2 surface is a little larger than that for the 180−cm2 surface. (2) is wrong because there is no comparison with other readings to decide what constitutes large friction. (3) is wrong because the experiment did not vary weight distribution. (4) is wrong because the same object was used throughout.
