Question

12. (12 Points) A student is interested in high-performance racing. The student, while learning about high-performance racing comes across a research document that claims that rubber materiais experience a kinetic friction with concrete such that the frictional force is directly proportional to sliding speed. (a) Would this claim be valid for materials such as wood, glass, and metal? If so, why? If not, why not? The student wishes to experimentally test this claim. The student obtains a piece of tre rubber shaped like a rectangular prism and a long slab of concrete. The student has access to other materials commonly found in a high-school physics laboratory. (b) i. What additional materials would the student need in order to perform the experiment? ii. Outline a procedure that the student could follow to collect data that would be needed to test the claim. Be sure to explain how the materials listed above are used to make measurements. Include a labeled diagram. (C) Explain how the student would analyze the data in order to test the claim

Answer 1

Solution

a)

Rubber is made of long carbon polymer chains with hydrogen attached along the length the chain. Almost any atom or molecule will try to stick to those hydrogen atoms. So rubber has more friction because it can flex enough to have more atoms available for interaction than almost any other material and because those atoms are “stickier” than the atoms present in most other materials. It has high surface area of contact as well which means more molecules interact and thus more friction.

This is not same in case of metals or wood which relatively stiff and has low contact area.

b)

Apparatus required rubber slab, weighing machine, mass of an object greater than the rubber slab, pulley, scale, stop watch, slab of concrete and strings Firstly weigh the two masses given and record it. We take the concrete slab and mark 1 m, 2m, 3m length with the scale and place the rubber slab on the opposite end of the slab. We connect the rubber with mass through the pulley attached as shown in the figure. We release the mass and and the stop watch to record at what time the pulley reaches marked lengths. We record the time.

3m 1m 2m

Analysis

We find the friction force acting on the rubber

Let a be acceleration of both the objects

For the mass W

W- T = W/g * a

For the rubber

T - W_rubber - f = W_rubber / g *a

From the two equations

f = W - W_rubber - (W- W_rubber) / g *a

We can find velocity and acceleration from the data recorded for 1m, 2m and 3m time taken.

Once we find acceleration we find their corresponding frictional value f

We then compare the value by taking the ration of frictional force and velocity. If it is nearly same then the experiment is successful.

If any doubt feel free to comment

P.S I thought this on my own I have not found or did any such experiment.