Objective Demonstrate static and kinetic friction, and see how friction changes when the surface is different
Materials Rubber band Shoe with rubber bottom Ruler
Procedure Weigh shoe Cut rubber band and tie one end to the shoe Set shoe on asphalt and start pulling on the other end of the rubber band until the shoe starts to move Use ruler to measure how far the rubber band stretches before the shoe moves Once it’s moving measure how far the rubber band is stretched Compare measurements Repeat steps 3-6 on concrete instead of asphalt
Static and Kinetic Friction After comparing measurements, we found that the rubber band stretches farther before the shoe starts to move. This is because it has to overcome static force for it to move. Once it was moving, the stretch of the rubber band wasn’t as much, because then it was just being influenced by kinetic friction.
Calculating Friction To find the value of the frictional force, you multiply the weight of the object by the frictional coefficient. For the first trial, we used the rubber bottom of a shoe on asphalt. That coefficient is 0.9, so we multiply the shoe’s weight by 0.9 For the second trial, we used the rubber bottom on concrete, and that coefficient is 0.7. Then we multiply the weight by 0.7
Friction and Newton’s 3 rd LawFriction is related to Newton’s 3rd law (every action has an equal and opposite reaction). When you try to push or pull an object, a frictional force is always acting against that motion, whether it’s in the air or on another surface.