Slip Sliding Away: Experimenting with Friction
| Difficulty | |
| Time Required | Very Short (≤ 1 day) |
| Prerequisites | None |
| Material Availability | Readily available |
| Cost | Very Low (under $20) |
| Safety | No issues |
Abstract
As you headed up the mountain to enjoy your last ski trip, you may have noticed a sign reading: Hazard! Icy Roads Ahead—Put On Your Chains. Putting chains on car tires increases the resistance between the tires and the road allowing the car to "grip" the road. This resistance to sliding is called friction. In this experiment, you will be investigating how to increase and decrease the friction between two surfaces.Objective
The goal of this project is to compare friction between dry and icy surfaces by measuring slip angle and slip height.
Credits
La Né Powers
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Last edit date: 2013-02-16
Introduction
Friction is the resistance to motion when two objects rub together.
For example, would it be easier to ride your sled down an icy snow-covered hillside or down a rough gravel driveway? It is easier to ride your sled down the icy hillside because both the runners on your sled and the hillside are smooth and slide past one another with little resistance. The icy hillside is an example of a surface with low friction.
Riding your sled down the gravel driveway is difficult due to the rough surface of the driveway resisting the motion of the sled. The gravel driveway is an example of a surface with high friction.
Terms and Concepts
- friction
- motion
- resistance
- gravity
Questions
- What is friction?
- How can friction be overcome?
- When is high friction beneficial? When is it not beneficial?
- When is low friction beneficial? When is it not beneficial?
Bibliography
- Introduction to General Physics Concepts:
Hewitt, Paul G, 2002. "Conceptual Physics," Prentice Hall, IL. - Simple Physics Concepts for Kids:
Keller, R.W., 2005. "Real Science for Kids: Physics, Level 1," Albuquerque, NM: Gravitas Publications, Inc.
Materials and Equipment
- 2 2×4s cut to 0.5 m length (about 20 in)
- small plastic tub or jar with lid
- sand
- water
- freezer
- books
- metric ruler
- protractor
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Experimental Procedure
- Soak one piece of wood in water and freeze overnight.
- Fill the plastic tub with sand and close the lid.
- Build a ramp using several books and the piece of wood.
- Determine the ramp height and ramp angle at which the tub of sand first slips down the ramp.
- Place the tub of sand onto the ramp.
- If it slips down the ramp, remove the tub, lower the ramp height and try again.
- If it does not slip, remove the tub, raise the ramp height and try again.
- Make your changes in height small enough so that you can accurately determine the ramp height and ramp angle just high enough to allow the tub to slip down the ramp.
- At the angle that the tub first moves, measure the height of the book pile with the meter stick and the angle of the ramp with the protractor. Record your results.
- Conduct the same experiment (steps 2–5) with the icy wood.
- For any experiment, it is important to do multiple trials to assure that your results are consistent. Repeat steps 2–5 for at least three separate trials for each surface, and record your results. It will be easier to keep track of your results if you write them down in a table in your lab notebook. Here is a sample table for data collection:
Sample Data Table Condition
(name)Trial
(#)Slip Angle
(°)Slip Height
(cm)Average Slip Angle
(°)Average Slip Height
(cm)Dry Wood 1 2 3 Icy Wood 1 2 3
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Variations
- Conduct the same experiment with two dry surfaces—increase the friction by covering one board with sandpaper.
- Cover the surface of one piece of wood with oil or foil to decrease the friction.
- Instead of changing the surface of the wood, change the bottom of the tubs by rubbing with oil or covering with sandpaper.
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