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# How Weight Affects Friction.

Extracts from this document...

Introduction

Friction Assessment

Planning:

The three factors that affect friction between surfaces are:

Weight (Mass)

Surface type (Roughness)

Area of Contact

I will investigate how weight affects friction.

I will keep the other factors constant to make it a fair test.

## Trial Experiment

I will choose the 100g masses.

I will choose the 95g sled.

I will take 5 numbers of readings.

My range will be from 0g to 1kg.

I will repeat each reading by 2 times.

### Reasons

I chose to use the 100g masses because they are easy to read and covers the required range.

I chose the 95g sled because the sled could hold more weight than the 31g sled, it is easier to read and easier to plot.

I chose to take 5 numbers of readings because it fits with my range. I will go up by 200g for each reading.

I chose to use my range from 0g to 1kg because it is easy to read.

I will repeat each reading 3 times, I will repeat readings and take average so that it will be a fair test.

### Trial Results

#### Mass of sled

(g)

(g)

Total Mass

(g)

Frictional Force (N)

Average

Friction

95

200

295

0.2             0.2          0.2

0.2

31

200

231

0.1             0.1          0.1

0.1

Middle

Smoother surfaces make for closer contact; the surfaces get close enough for atoms so they attract making them stick together. There is no such thing as the smoothest surface because even the smoothest surface is rough on an atomic scale. Therefore even two very smooth surfaces are in close contact at only a few points. This diagram shows this:

Thus the weight of an object with a smooth surface is supported at a few points of contact. The area of these points of contact is very small. The weight of the object divided by the total area of contact (resulting pressure) is huge. When these high pressures occur, atoms of one surface are pushed close enough to the other surface that they attract one another as strongly as they would if they were all part of the same surface. Due to this the two surfaces fuse (melt or weld) together at those points.

The surface area of the object does not affect friction because the total area of contact at these points is small compared to the total surface area of the object.

Conclusion

To make the experiment more accurate mechanical apparatus should be used that is capable of measuring by itself without human help, this would help greatly to the accuracy of the experiment. Due to the time limitations of the experiment each mass and sled in existence could not be tested to see if it gave clearer results also due to time limitations if the experiment was repeated 10 times the average fiction would be more accurate.

The results were reliable because all the plotted points were near the line of best fit and there were no anomalous results.

I could also investigate how surface area affects friction or use a different range of masses.

Bibliography.

http://physicsweb.org

Physics by Stephen Pople and Peter Whitehead

Britannia Encyclopedia

By Oktavis Gousevnis

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

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