ACTIVITY 8TRACTION SURFACES AND FRICTION Fast Fact:
Warming up for the start of a race, drivers zigzag, raising the temperature of their tires to improve traction. When cornering on the track, racing tires can reach temperatures of up to 188C (370F).
Objective:
The students will investigate the effects of friction and how different surfaces can affect the amount of friction.
In the Film:
The race cars sole connection to the track is through the contact patches, or footprints, of its four tires. Different weather conditions require different tires and driving strategies. In the film you see weather conditions vary from race to race. Starting, slowing, passing and turning are all affected by weather and track conditions.
Background:
Friction is a slowing force caused by interactions between surfaces rubbing together. These interactions may be the result of cohesion or of molecular vibrations. If the interactions can be controlled, the friction can be controlled.
Materials:
Any toy car or truck, a ramp, paper, sandpaper, various kinds of tapes, plastic wrap, and sand or flour.
To Do:
Have the students fold a piece of paper and tape it to make a pocket. This pocket will capture the toy car as it leaves the ramp (see illustration). Ask the students to roll the car down the ramp into the pocket and measure how far along the flat surface the pocket slides until it stops. They may do this a number of times to get an average sliding distance.
Now have the students put tape on the underside of the paper pocket so that the pocket will slide on the tape instead of the paper. Repeat the experiment and note how far it slides. Repeat the experiment with a variety of different textures placed on the flat surface such as sandpaper and plastic wrap, with and without the tape. Finally, have the students sprinkle a tiny amount of flour over the flat surface to see how this affects the results.
Whats Going On?
The friction force slows the pocket in each trial. The larger the force, the shorter the distance the pocket will travel. For example, the plastic wrap sticks to the table more readily than the paper because the molecules of the plastic are more cohesive. The pocket will stop in a shorter distance when sliding over the plastic wrap than over the paper. The flour reduces the molecular interaction, allowing the car to slide further.
Taking It Further:
1. Have the students try rolling the car from different ramp heights. If it is twice as high, does it slide twice as far?
2. Tell the students to place weights inside the pocket. How does this affect the distance of the slide?
3. See if the students can explain why different tires are used on a race car when it rains.
4. Have the students consider when it might be advantageous to have a lot of friction. What parts of a race car should have lots of friction?
5. Have them consider when a lot of friction is a disadvantage. What parts of a race car should have very little friction? Ask the students how this knowledge might be used to improve the car they designed in Activity 1.