Determination of Coefficient of Friction

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DETERMINATION OF THE COEFFICIENT OF FRICTION

Aim:

  1. To determine µ kinetic between a wooden block and a wooden plane;
  2. To determine µ static between a wooden block and a wooden plane.

Equipment:

  1. Wooden block;
  2. Wooden plane;
  3. Spring scale;
  4. Meter rule;
  5. Weights.

There are two parts of my investigation, so I will precede them separately.

Determination of µ kinetic between a wooden block and a wooden plane

This is the table which I filled during my determination:

Recording raw data:

First of all, I prepare my working place and start my determination. All my measurements are recorded to the table above. For more accurate results of µ kinetic I recorded data with 5 different weights.

The smallest graduation of the spring scale is 0.1 N. According to this, the absolute uncertainty of weight of the block is ±0.05 N.  I do not add additional uncertainty as I did not encounter any further difficulties in weight measurement.

I used weights provided by my teacher. Those weights were precisely 1 N each. In the table I only provide the number of them and therefore I take it without uncertainty.

Once again the smallest graduation of the spring scale is 0.1N and according to this, the absolute uncertainty of friction force measurements should be ±0.05N, but I decided to take this uncertainty as ±0.1N as it was hard to determine the friction force correctly. I needed to pull the block with the weights at just that force to overcome the friction. I needed to pull equally and using the constant force. It was hard to do, so I decided to add some further uncertainty.

Data processing:

When determining the kinetic friction coefficient the mg is equal to the normal force. In each situation I add the weight of the block with weight of the number of weights added. As my used weights were very precise and provided by my teacher I do not include uncertainty to their weights. They were 1N each. Therefore, I leave the absolute uncertainty of the normal force the same as the weight of the block as the same uncertainty remains. ∆Normal force = ∆weight of the block + ∆weights -> ∆normal force = ∆weight of the block + 0.

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For each situation with different number of weights, the normal force differs as well. I calculated the normal force in this way:

Normal force = weight of the block + n x weight of one weight -> Normal force = 0.60 + 1n, where n is the number of weights added.

When I added 0 weights, normal force = 0.60 N;

When I added 1 weight, normal force = 1.60 N;

When I added 2 weights, normal force = 2.60 N;

When I added 3 weights, normal force = 3.60 N;

When I added 4 weights, normal force = 4.60 ...

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