In this experiment, you will investigate the friction between a training shoe and different floor surfaces. You places the shoe sole-down on a floor surface...

(a) The newton meter reads 7.4 N. [1]

(b) The weight of a 2.0 kg mass:

\[ W = mg = 2.0 \times 10 = 20 \text{ N} \]

(Using \(g = 10\) N/kg. If using \(g = 9.8\) N/kg: \(W = 2.0 \times 9.8 = 19.6\) N.) [1]

Weight is the gravitational force acting on a mass, calculated by multiplying mass by gravitational field strength.

(c) Two variables kept the same to make this a fair test:

1. The same shoe used for all surfaces, so the sole material and tread pattern are identical.
2. The same mass (2.0 kg) inside the shoe, keeping the normal contact force constant.

Other acceptable answers: pulling at the same angle (horizontal), keeping the same area of sole in contact with the surface. [2]

(d) Pulling at a steady speed means the shoe is in dynamic equilibrium: the net force on it is zero. The forward pull from the newton meter exactly equals the backward friction force. If the shoe were accelerating, the newton meter reading would include the force needed for acceleration, and would not equal the friction force alone. [1]

(e) One improvement: repeat each measurement three times on each surface and calculate the mean friction force. This reduces the effect of random variations in the readings and gives a more reliable result. Alternatively, use a data logger with a force sensor instead of reading by eye, which reduces human error. [1]

(f) On a wet tiled floor, the water acts as a lubricant between the shoe sole and the tile. The thin layer of water reduces direct contact between the two surfaces, lowering the friction force compared to a dry tile. [1]