Additional Project Ideas

Hey Gear Heads! The Physics of Bicycle Gear Ratios
If you have a multi-speed bike, you know that you can make it easier or harder to pedal just by shifting gears. Ever wonder how that works? You can investigate this a number of ways. A basic approach is to use a selection of spools of thread (with different diameters), a board with two nails, and a rubber band. Place a spool over each nail, and put the rubber band over them. Mark the 12:00 position on each spool so that you can count revolutions. Turn one spool through a full circle and note how far the second spool turns. Try with different combinations of spool sizes. Explain how your results relate to bicycle gears. You can also do this with a multi-speed bike: turn the bike over, and mark a position on the rear wheel with tape so you can count revolutions. Or, maybe your bike has a speedometer and cadence monitor (this uses magnets on the crank and wheel, and fixed sensors mounted on the frame to count). Have a helper hold the rear wheel up while you move the pedal at a fixed cadence (make sure there is no slack in chain). Record the resulting speeds for each gear combination. Count the teeth on the front sprockets and rear gears. Divide the number of teeth in front by the number in back for each gear combination. Knowing the wheel circumference, you can calculate the wheel's angular speed (revolutions per minute, or rpm's) from the recorded speed. Graph your results. Is there a relationship between the ratio of the gear teeth and wheel rpm's? (Idea from Wiese, 2002, pp. 62–67.)
Wiese, Jim. Sports Science: 40 Goal-Scoring, High-Flying, Medal-Winning Experiments for Kids. New York: John Wiley and Sons, 2002.

Air Pressure and Rolling Resistance
How does the air pressure in a tire affect the rolling resistance of a bicycle or wheelbarrow? Do you need more or less effort to move the bicycle (or wheelbarrow) as the air pressure is changed? Use a tire pressure gauge to monitor air pressure (don't exceed the recommended tire pressure). For the bicyle, you could probably use a spring scale to measure how much force is needed to pull the bicycle along (have a friend lightly touching the bike to keep it balanced). Quantifying the force needed to move the wheelbarrow will be a bit more difficult. You may have to resort to a 1–5 rating scale (e.g., where 1="I can do this all day," 2="takes a bit of effort," 3="a good workout," 4="pushing myself pretty hard," and 5="maximum effort.") For more advanced students, can you explain your results in terms of frictional forces?

Physics of Vibrations
Tennis racquets, baseball bats and golf clubs all vibrate when they hit the ball. You can often feel it in your hands, particularly if you "mis-hit" the ball. You can find the point(s) on your racquet, bat or club—called the "sweet spot"— that minimize unwanted vibrations. Low-tech method: hang the racquet or bat straight up and down with a string from its handle. Lightly hold the handle with your thumb and forefinger and have a helper sharply tap the bat, strings or club face with a ball at regular increments along the length. You'll feel a minimum in the vibration at the "sweet spot" of the bat, racquet or club. High-tech method: loosely tape a card to the handle so that it will vibrate when the racquet, bat or club is tapped (Brody, 1987, p. 33). If you want to go all out, you can measure the vibration of the card by monitoring light reflecting off the card with a photodiode and analog-to-digital converter. Several projects possible: longest hit from where? best accuracy from where? comparing different racquets for comfort? (Both Brody et al., 2002, and Brody, 1987, have extensive sections on the vibration of racquets; Barr, 1990, pp. 37–39, has a short treatment of vibration in baseball bats.)
- Barr, G., 1990. Sports Science for Young People. New York, NY: Dover Publications.
- Brody, H., 1987. Tennis Science for Tennis Players. Philadelphia, PA: The University of Pennsylvania Press.
- Brody, H. et al., 2002 The Physics and Technology of Tennis. Solana Beach, CA: Racquet Tech Publishing.

Skiing and Friction
How does ski wax affect the sliding friction of skis? You can model this with an ice cube sliding down a plank: how high do you need to lift the end of the plank before the ice cube starts to slide? Try this with one side plain wood and the flip side waxed wood (use paraffin wax, candle wax or ski wax). Make sure both sides are equally smooth to start with. Do at least three trials. More advanced: using what you know about the forces acting on the ice cube, derive equations to calculate the coefficient of friction for each case. Variation: chill the planks to different temperatures (e.g., inside, vs. outside, vs. enclosed, but unheated porch; or use your freezer; make sure the boards stay long enough to reach equilibrium). Do tests at steady temperature, try different cross-country ski waxes at each temperature. (Idea from Wiese, 2002, pp. 54–56.)
Wiese, Jim. Sports Science: 40 Goal-Scoring, High-Flying, Medal-Winning Experiments for Kids. New York: John Wiley and Sons, 2002.

The Turn of the Screw
How much force is required to advance a lag bolt (large wood screw with a hex-shaped head) into a piece of wood? You can measure the force by using a spring scale attached to the handle of ratchet. Pull on the spring scale until the bolt starts to turn, and note the required force from the spring scale. There are many potential experiments you could try. Think about answering the following questions: How does the force change as the bolt advances deeper into the wood? Why? How does the required force change as the diameter of the pilot hole is changed? Why? Can you change the required force by rubbing the bolt's threads with soap or wax? (Coyle, 2005)
Coyle, C.P., 2005. "Some Variables Affecting the Torque Required to Turn a Screw," California State Science Fair Project Abstract [accessed April 18, 2006] http://www.usc.edu/CSSF/History/2005/Projects/J0205.pdf.

Effect of Temperature on Elasticity of Rubber Bands
How much force can a rubber band withstand before breaking? Do rubber bands that stretch longer take more or less force to break? How does the elasticity of a rubber band change with temperature? Use a spring scale to measure the applied force, and a meter stick or ruler to measure the change in length. Recording with a video camera (or possibly two) can help you to capture the values at the moment before the rubber band breaks. You can change the temperature of the rubber bands using heated or cooled water. (Coy, 2005)
Coy, A.R., 2005. "How Does Temperature Affect a Rubber Band's Elasticity?" California State Science Fair Project Abstract [accessed April 18, 2006] http://www.usc.edu/CSSF/History/2005/Projects/J0204.pdf

Domino Theory
Have you ever set up a line of dominoes and watched them fall? If you wanted to make your line of dominoes fall faster, do you think you should set the dominoes up with more or less space between them? Set your dominoes up in a straight line, using a ruler to keep the spacing between them constant. Try different spacings at 0.5 cm increments. Conduct multiple trials at each spacing, and time how long it takes for a fixed total length of dominoes to fall (e.g., a 1.5 or 3.0 meter length of dominoes). Average your results for each spacing. At which spacing do the dominoes fall the fastest? Can you explain your results? Can you predict the optimal spacing for a set of taller (or shorter) dominoes? Find another set and test your prediction! (Gatanaga, D.A., 2004)
Gatanaga, D.A., 2004. "How Does the Distance Between Dominoes Affect the Speed That Dominoes Fall?" California State Science Fair Project Abstract [accessed April 18, 2006] http://www.usc.edu/CSSF/History/2004/Projects/J0211.pdf

Resources

Sources for Additional Project Ideas

Coy, A.R., 2005. "How Does Temperature Affect a Rubber Band's Elasticity?" California State Science Fair Project Abstract [accessed April 18, 2006] http://www.usc.edu/CSSF/History/2005/Projects/J0204.pdf.
Coyle, C.P., 2005. "Some Variables Affecting the Torque Required to Turn a Screw," California State Science Fair Project Abstract [accessed April 18, 2006] http://www.usc.edu/CSSF/History/2005/Projects/J0205.pdf.
Barr, George. Sports Science for Young People. New York: Dover Publications, 1990.
Brody, Howard. Tennis Science for Tennis Players. Philadelphia: The University of Pennsylvania Press, 1987.
Brody, Howard et al. The Physics and Technology of Tennis. Solana Beach, CA: Racquet Tech Publishing, 2002.
Gatanaga, D.A., 2004. "How Does the Distance Between Dominoes Affect the Speed That Dominoes Fall?" California State Science Fair Project Abstract [accessed April 18, 2006] http://www.usc.edu/CSSF/History/2004/Projects/J0211.pdf.
Wiese, Jim. Sports Science: 40 Goal-Scoring, High-Flying, Medal-Winning Experiments for Kids. New York: John Wiley and Sons, 2002.