Question 1. Which of the surface pairs had the least friction? If you tried a liquid interface,or ice,comment on the difference between the dry and liquid instances. From your experience doing this simple experiment, what would you choose to (a) allow a heavy piece of furniture slide on the floor to move it, and (b) prevent slipping on a sloped sidewalk in wet weather?

Question 2. Provide your data on the surfaces you used. We requested that you do this for at least three pairs,for example wood could be the ramp and a cardboard box might be the load sliding on it. List the pairs, and for each one give the angle at which the object started to slide. This should be the angle of the lower surface to the horizontal. measured as you described in #1. For each angle compute its tangent, which is the coefficient of static friction for this pair of materials.

Question 3. Which of the surface pairs had the least friction? If you tried a liquid interface,or ice,comment on the difference between the dry and liquid instances. From your experience doing this simple experiment, what would you choose to (a) allow a heavy piece of furniture slide on the floor to move it, and (b) prevent slipping on a sloped sidewalk in wet weather?

An ideal way to do this experiment is to reproduce what they have done at home with a convenient board (a shelf pehaps) and your cell phone with a level application that will tell you how much it is tilted. However you can also

• use any flat surface - inside a drawer, a cutting board, or a the hard cover of a large book
• measure the tangent directly - the ratio of the rise to the run or y/x is the tangent of the angle to the horizontal
• select several different surface pairs

Start with the materials in contact on a flat horizontal surface and raise one end until the object starts to slide. Find the angle either by direct measurement or the geometry.

What is the coefficient of static friction for that surface pair?

Repeat for 3 or more materials. Select two of them to have at least one that will not move easily and will require a large angle, and another that will slip readily and start to slide at a small angle. If possible try a pair with and without water at the interface, or even some ice. An application is obviously how you can slip on wet surface, or how a car may skid on ice.