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One of the physical phenomenon that you encounter everday is friction. Yet it is something that scientists really don't completely understand yet. Today we will examine friction and see if we can come up with some characteristics of friction.

Part 1: Discuss with your neighbor the following questions and write down what you come up with. What do you think causes friction? What are some of the consequences of friction?


Also be sure that when you pull on the box that the string and scale are parallel to the tabletop or the floor.

Part 2: Let's do some experiments to help us figure out some general properties of friction by using a spring scale which will measure the frictional force for a box on the table. Place a two kilogram (kg) mass in the box. Now measure the force it takes to just get the box to move. Add a one kilogram mass and repeat this measurement. Do this again by adding another one kilogram and continue until you have measurements for 2, 3, 4 and 5 kilograms. What do you notice about the force needed to just get the box to move?

Part 3: Repeat the above experiment but now measure with the box on the carpet in the hallway. Do you get the same frictional force for the same mass as in Part 2? What can you generally say about the forces needed on the carpet versus the forces on the table top?

Part 4: Repeat the experiment described in Part 2 only now measure the force needed to keep the box moving at a constant speed for the different masses. Are your results the same as in Part 2? What does this tell you?

Part 5: Do you think that the frictional force depends on the surface areas touching? Let's do an experiment to test this. With a 2 kg mass in the box what frictional force does it take to just get the box to move (remeasure it)? Rotate the box so that a different side is touching the tabletop. Again with the 2 kg mass in the box what force is needed to just get the box to move? Is this force the same as with the other surface? What can you now say about "Does the frictional force depend on the surface area?"

Summarize your experimental results from today.