|MadSci Network: Physics|
You have quite a project to accomplish! It is not my intent to do your homework, but I can help. You probably can figure out what materials would work from your own experience. What has good traction when wet? If your answer was a rubber tire--you are correct. Now think about what kind of tire treads are used on wet roads, and what types on dry. Drag racers only operate on dry road surfaces, and have no tread, and very high surface area contacts. If you have seen the tires used on sports cars for wet roads, you may see that the treads have many sipes, cuts that cross the rubbing path. Wet road tires also have higher contact pressures than dry road tires. If you think about it, the higher contact pressure helps force water away from the contact. This increases friction by decreasing the lubricating effect of the water. You did not indicate the size of the vehicle you are building. Model shops carry tires of different sizes for model cars and aircraft. If building a larger vehicle, you might want to try a lawnmower tire, with added saw cuts across the tread to increase wet traction. If larger yet, a bicycle tire may be used. Remember to keep the contact pressure high enough to remove the water. Avoid foam rubber tires. Another point to consider. Cleanliness affects friction--by a large amount. You would do well to consider a careful cleaning of the tire rubbing surfaces. Oil and solid particles must be removed. Laundry or dishwashing powder detergents are good. Rinse well, and then rinse again with some alcohol. Then do not touch the tires, as your fingers will likely contaminate the tires with oil. Finally, run an experiment before the final test. This is how you learn about friction, and the variables that affect it. You might try different solvents on the tires to see how they affect traction. You also may want to try narrowing the tire tread width. Higher contact pressures usually help wet friction, as long as solid (not foam) rubber is used.
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