Slip Sliding Away: Experimenting with Friction
IntroductionHave you ever driven up a mountain, seen a sign reading "Hazard! Icy Roads Ahead," and wondered why ice makes roads dangerous to drive on? The answer has to do with friction—specifically, the lack of it.
Specifically, in the case of driving a car down the road, the friction that allows the car to move occurs between the tires and the road. This friction normally allows the car to "grip" the road—keeping the tires in contact with the relatively rough road surface, and the driver of the car in control. However, when the road is icy, the friction between the two surfaces decreases, allowing the car to slip—rather than grip. You can replicate these situations much more safely at home using some common objects—regardless of the weather.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
BackgroundFriction is the resistance to motion when two objects rub together. An example of low friction is when you sled down an icy hill. It's easy because both the sled and the ice on the hill are smooth and the surfaces of the sled's runners and the ice slide past one another with little resistance. On the other hand, sledding down a rough, concrete driveway is almost impossible due to the rough surface of the driveway, which provides resistance on the sled's runners. This is an example of high friction.
As you can imagine, friction happens when the rough parts of two objects catch one another as they rub together. The resistance that occurs depends on a value called the coefficient of friction. This is a measure of how much two objects interact with one another when rubbing together, and this depends on the materials that make up the two objects. The friction that takes place also depends on the mass of the moving object in the pull of gravity. All of these factors play a role in determining how much friction there is between two rubbing objects.
Extra: How easily would the tub slip on a ramp made of other materials? Make a similar ramp using a plank covered with sandpaper, oil or aluminum foil. Alternatively, cover the bottom of the tub in these materials. How easily does the tub slip using the different materials?
Extra: If you know the ramp's height and length, you do not need a protractor to figure out its angle. All you need is to do some math: The equation used to solve the angle of the ramp is sin(theta) = opposite/hypotenuse. In the formula, "sin" stands for sine, "theta" is the angle, "opposite" is the ramp height and "hypotenuse" is the ramp length. Find out more about how to do this calculation at "Finding an Angle in a Right Angled Triangle" from Math is Fun Advanced. Does the calculated angle match the one you measured with your protractor?
Observations and ResultsIn general, did the tub slip down the icy ramp better than the dry ramp? Was the smallest ramp angle needed for the tub to slip on the icy ramp smaller than the angle needed on the dry ramp?
When two objects rub together, there is always friction, and the surfaces of the two objects determine the amount that is generated. In this activity, you should have seen that there was less friction between the tub and the icy wood than from the dry plank. In other words, a smaller ramp angle was needed when using the icy wood than when using the dry wood for the tub to slip.
To calculate the force of friction, one must multiply the coefficient of friction by the force generated by the object, which was the mass of the tub in the pull of gravity. Although the mass of the tub and gravity did not change, the coefficient of friction of the two ramp systems did. The icy plank and the tub bottom had a lower coefficient of friction than the dry wood and the tub. You can easily feel this difference by carefully running your hand along the icy and then dry wood surfaces. The icy plank's frozen coating makes it much smoother than the dry wood.
More to Explore"Friction" from Kidipede, History and Science for Kids, Portland State University
"Moti" from Motion Basics: Friction from Rader's Physics4Kids.com
"Finding an Angle in a Right Angled Triangle" from Math is Fun Advanced
"Slip Sliding Away: Experimenting with Friction" from Science Buddies
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Physics, friction, mass, gravity
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