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Investigating Sliding Friction: the effect of weight on sliding friction between a block and surface.

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Frankie Bright 11B

Investigating Sliding Friction: the effect of weight on sliding friction between a block and surface.


In this investigation we are going to find out what effect weight has on sliding friction. Friction is the force that is between two objects that are in contact with each other. The force is always present even though people only think it is there when the object is moving. Leonardo da Vinci was one of the first people to experiment with the idea of friction. He came up with two types of friction; static friction, which is the friction, which is present when the object is stationary and kinetic friction, this type of friction is present when the object is moving. Static friction is greater than kinetic friction. Kinetic friction is the type we are going to be investigating. Kinetic friction occurs when the surfaces of the two objects move against each other. Even if the surface appears completely smooth there will always be minute bumps and lumps on it. The lumps on the one surface move against the lumps on the other surface and produce the force of friction.

I predict that in this experiment if you double the weight the friction on the object will also double. I have based this prediction on the formula shown below.

...read more.


Nine 100gram weightsFlat surface that will stay continuously at the same angle



  1. Firstly I am going to set up the equipment as shown in the diagram above
  2. I will then pull the wooden block until it is moving at a steady speed. I will do this because according to Newton’s first law of motion Newton said


This means that when an object is moving at a steady speed the two forces acting on the object are equal. I will use this information to record the force of friction because when I pull the block my pulling force will be measured on the Newton meter, so therefore if the block is moving at a steady speed the force of friction will be the same as my pulling force.

  1. Once the block is moving at a steady speed I will record the results.
  2. I will then repeat this but place one of the 100g weights on top of the block, so as to increase the weight.
  3. Once I have added the extra weight I will pull the block across the foam until yet again it is moving at a steady speed.
  4. I will again record the results.
  5. I will continue adding the weights one at a time until all of the weights have been used up and I will record the results each time.

...read more.



I feel that, my results were relatively accurate though I do feel that they could be improved by having a Newton meter that has more accurate readings. For this experiment however I think that the results are accurate enough to prove the theory and my prediction. The force of friction did in fact double when the weight of the object was doubled. This reverts back to my prediction and the workings of Leonardo da Vince and another man called Guillaume Amontons. He said  

“The friction made by the same weight will be of equal resistance although the area of contact may be different lengths and breadths; the friction produces double the amount of effort if the weight is doubled.”

Amontons said that he noticed patterns of behaviour when two surfaces moved against each other. He said that the roughness of the surfaces was to blame for this. They were proved to consist of minuscule dip, mountains and cavern that interlock with each other as they pass over one another. By raising the upper object, in this case it is the wooden block; you would reduce the amount of friction. So therefore by pushing harder on the upper object you would increase the friction and a greater force would be needed to pull the block and this proves my results and my prediction.

...read more.

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