Physics Core/AP 1 and 2

Physics Lab

# Physics Lab: Inclined Plane with Friction

## Goal: to become familiar with force measurements when a non-conservative force (friction) is involved.

#### Materials and Equipment

• an elevated surface on which you can slide things without worrying about scratching it. [scrap wood on a table will work--but it shouldn't be too rough].
• a pulley you can clamp to the edge of your surface. If you can't find a pulley, reduce the friction at the edge by using a roll of plastic tubing along the edge.
• several sliders: such as a block of wood, a bar of soap. They should have flat surfaces where they will be in contact with the support surface.
• pins, tape, or other means of fastening string to your slider.
• string
• a set of standard weights (I like using coins; try to weed out any that are too worn). These do not have to be any particular unit, but they should all be the same.
• a bucket, sack, or other means of keeping the weights together.
• blocks or other means of inclining your slide surface
• stop watch
• protractor

#### Procedure

1. Record your hypothesis: do you expect the static friction for a given slider to be a constant, or will it depend on the angle of the sliding surface?
2. Weigh your slide. If you still have your equal arm scale, you can use that. If necessary, just get the weight of your slide in equivalent standard weights (e.g., 95 nickels). If you use a cup to hold your weights, you should weigh it also and include its weight along with your standard weight for total weights below.
3. Fasten the pulley or tubing to your surface edge.
4. Fasten the string to your slide
5. Run the string over the edge of the tubing so that it hangs down; fasten your cup or other weight holder to the end.
6. Start adding weights to the end of the string.
7. Record the total amount of weight required for your slide to start moving.
8. Repeat the above procedure with another slide which has a noticeably smoother or rougher surface.
9. Repeat the above procedure for each slide with the slide surface inclined at approximately 10° and at 15°.
10. Make a table which shows the mass of the slide, the normal force for each trial, and the weight required to overcome static friction. Determine the static friction.
11. Estimate errors for each of your measurements.

#### Data Handling

Data Reduction

Display your information appropriately in table format. Use data reduction techniques such as those outlined in the Data Handling section of the Falling Bodies lab to analyze your data.

Determine the dependence of acceleraton on the angle of inclination and the amount of friction. Is this a linear function? A non-linear function? How can you show this?