Question 6
In activity 03 the sandpaper stuck to the different faces of the block must all be of the same roughness. Why?
The right answer is the one marked above.
So that the area is the only thing being changed. If the roughness varied too, a change in the reading could be blamed on either factor and the experiment would prove nothing.
This is the fair-test rule behind all three activities: change one factor, hold the rest steady. Activity 02 varied the roughness and kept the block the same; activity 04 varied the weight and kept the surfaces the same.