Question

In our experiment we used a block with different materials on its sides. One side was wood, the other was felt, the last was cork. We then used attached a string to the block and put that over a levey. At the end of it was a hanging mass. The mass of the block mentioned in the questions below is in reference to the mass of the block on the horizontal surface (not the hanging mass) Please answer the questions conceptually. If you feel the need to mark this question as "needs more information" then please do not attempt to answer this question. I appreciate the help.

1. How does the coefficient of kinetic friction vary with the mass of the block?

2. Which has a greater effect on the force of kinetic friction, continually increasing the mass of the block or changing the type of materials in contact? Cite your data and explain your answer.

3. How does the coefficient of static friction compare to the coefficient of kinetic friction for the same surface material. (woode felt, and cork)

Answer 1

1. The coefficient of friction is a property of type of material and does not depend on the mass of the body. Frictional force depends on mass of body but not the coefficient of friction.

2. Changing the type of material in contact will have greater impact because force of friction depends on normal force and coefficient of friction. So normal reaction from a surface may not necessarily depend on mass of block. Hence the force definitely depends on coefficient of friction and hence changing that will have most impact.

3. The coefficient of static friction is always greater than coefficient of kinetic friction for all type of materials ( same surface of material)

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