The Starting Line
Do you feel the need ... the need for speed? Racing cars is just fun, and building your own racecars adds to the excitement. But science is also involved in building and racing cars. If you want to build away, go ahead — you can always come back to this chapter later. But knowing about the science involved in your racecars is the key to making cars that roll farther and faster.
Ways to Power Your Racecar
Cars need energy to go. In a traditional car, that energy comes from gasoline. In the future more and more cars will run on electricity from batteries. But for the cars you are going to build, you will be using free and renewable sources of energy — rubber bands, mousetraps, chemical reactions, air pressure, and gravity. The key is getting that energy to spin the wheels.
How to Make Great Racecars
Friction is important for a good racecar. Friction is a force that opposes motion, but friction also keeps the wheels from spinning in place. A racecar driver never wants a wheel that spins in place.
Friction depends on two things: weight and the types of surfaces in contact. Rubber is a great material because it provides a lot of friction, which is why you play basketball, volleyball, and tennis in rubber-soled shoes. Wrapping a rubber band or a piece of a balloon around your wheels can increase friction, and off your car will go.
Weight is a tricky thing with your car. Too much weight and it won't go very far. But too little weight and the wheels will just spin in place. Adding weights like coins and soda cans may actually make some cars roll farther. Experiment to find the best combination to help your car go.
The key to science is experimentation. Feel free to modify any of the plans in this book if you have a better idea; you won't know unless you try.
To roll, you need wheels. Save every round thing you come across: CDs, bottle caps, jar lids, and plastic can covers (like those from Pringles cans) all work well. Another great source for wheels is old toys. Save the wheels from any broken toy before you recycle the rest. A relatively cheap and lightweight wheel can be found in stores that sell fake flowers. Round Styrofoam discs are used in floral arrangements and also make great lightweight wheels. You can also buy wheels at hobby stores, which sell a large variety of wheels for remote control cars and planes.
For maximum speed and distance, store-bought wheels are hard to beat. Many are made from high density foam, which leads to lightweight tires and great friction that blast off from the starting line. But store-bought wheels take cash and planning. Every racecar in this book can also be built with free wheels. Keep a box in your room with anything you might be able to use. If it's round, save it. Someday you may use it to help create world record racecars.
Growing up, my brother and I had to hide stuff from our trash monster: my sweet mom. She would have been more understanding if we had just explained the benefit of creative construction.
All wheels need axles. Axles can be fixed or rotating. A fixed axle is stationary; the wheel spins on the axle. A rotating axle is affixed to the wheel, and the entire wheel and axle combination spins.
Regardless of type, toothpicks and bamboo skewers make great axles. Bamboo skewers are toothpicks on steroids. Your parents may already have these around the house. They are also available at dollar, grocery, and big box stores. You can also buy metal rods or wooden dowels at most home improvement stores. They add to the cost, but sometimes it is worth it for a contest.
Mousetrap car contests are a great way for science to come alive. Designing and building a mousetrap car is fun and educational. Mousetrap car contests have one of two goals: the fastest speed or the longest distance. Modify your mousetrap car to achieve maximum results for your specific contest.
Another type of car contest is an edible racing battle, in which the car must be made primarily from edible parts. Fun, educational, and tasty! The rules may allow for toothpicks or skewers, so read the rules carefully. Regardless of contest type, you need to learn a little about energy so you can achieve the best results.
Energy is the ability to do work. And in science, work means getting something to move. Energy comes in two forms: potential and kinetic. Potential energy (PE) is stored energy. A stretched rubber band has stored elastic potential energy. Elastic materials will return to their original shape after being stretched. Elastic energy is most commonly found in rubber bands and springs. You will use both to power your racecars.
A box sitting on a high shelf has stored gravitational potential energy. Gravitational potential energy is energy an object has because of its position. Climbing a flight of stairs gives you more potential energy. Ramps will be used to give a few of your racecars the energy they need to go.
Once your car starts moving, the potential energy is converted into kinetic energy (KE, or energy of motion). The more stored energy you have, the greater kinetic energy you will get out. Play with a rubber band to understand this. Stretch it a little and shoot it. Now stretch it more and shoot it. More PE equals more KE, and KE means speed. And speed is fun.CHAPTER 2
Mousetrap cars — rolling machines powered by the spring of a mousetrap — are a ton of fun. Car design is crucial as you shoot for a world record distance or a world record speed. If you want a little more power, you can even go with a rattrap.
Mousetrap car contests are popular events for science olympiads. Participants are asked to build a car that will roll the greatest distance powered only by a single mousetrap. Adding a longer lever arm to the spring is the best way to create maximum distance. Other contests just measure speed over a set distance. If you participate in a mousetrap car competition, be sure to read the rules carefully. You will probably need to make a trip to the hardware or hobby store in order to create the best racecar possible, but there are a few plans that use mostly free and recycled stuff you already have around the house.
Take a close look at a mousetrap. A mousetrap consists of a wooden base, a spring, a hammer, a catch, and a holding bar. The energy of a mousetrap car comes from the spring. The metal spring is coiled around the base of a square called the hammer. The hammer is the part that snaps closed when the mousetrap is sprung by a cheese-loving rodent. A basic mousetrap also contains a catch, which is the platform for the cheese, and a holding bar, which holds the loaded mousetrap hammer until a mouse samples the cheese. You will only use the spring and the hammer for your cars. The holding bar and catch will be removed to save weight.
Wheel choice is very important on a mousetrap car, since bigger wheels will cover a greater distance each time they rotate. Think of the bicycles you have owned. As you grew, the wheels grew too and you covered more distance. Old CDs are probably your best free choice for wheels — the perfect way to repurpose discs that are no longer needed. Also, when you buy a package of blank CDs, they often come with at least one clear CD-sized plastic top (or bottom) to protect the actual CDs. These layers make great wheels, as they are even lighter than the CDs. Of course, many hobby stores sell lightweight remote control car wheels. These wheels are designed for speed and traction, but they will cost you.
Rubber faucet washers work the best to hold the CDs onto the axles. They are beveled and large enough to fill the CD center hole. They can be found in the plumbing section of any hardware store or large department store. Wooden dowels should be available in the same stores. A dowel with a 3/16-inch diameter works the best, but other sizes will also work. Take the dowel to the plumbing department and you can find a washer that will fit snugly around it.
Balloons or glue can be used to increase the traction on the wheels. This is another great way to increase distance. Adding lubricants to the axles will help the car roll easier; WD-40 and graphite powder are great choices for this. You will also need some scrap wood to attach to the car for size. For a mousetrap contest, lightweight wood is important. Balsa wood — the wood used in model airplanes — is the best choice because it has enormous strength for its weight. Balsa wood is available at all craft and hobby stores.
Many hobby stores and websites also sell mousetrap car kits. These kits will give you all the basic pieces and eliminate the need for much adult help. Kits are fun, but they can limit your creativity. A list of kit makers and websites is included at the end of this chapter.
Mousetrap cars can also be a great choice for science fair projects. Science fairs expect you to design an experiment and take measurements to reach a conclusion. Mousetrap cars are fun to build, and the distance they roll is easy to measure. You can vary the length of the lever arm or the wheel diameter and measure the rolling distance for each variation. You can also compare a rattrap car to a mousetrap car. Rattraps are larger and weigh more, but they have a more powerful spring. However, rattrap cars won't be allowed in most contests. Nevertheless, they are fun to build and play with.
Now it's time to start building some cars.
This basic design will get you started launching mousetrap cars.
Adult supervision required
Small piece of wood
4 screw eyes
4 old CDs
Fishing line or thread
Tape or cable ties
Step 1: Use needle-nose pliers to remove the mousetrap's holding bar. The holding bar is the long, straight bar that allows you to set the mousetrap.
Step 2: Use the pliers to remove the catch. The catch is the platform for the cheese bait.
Step 3: With an adult's help, drill a ½-inch hole in the end of a piece of wood near one end. This piece of wood will be glued to the base of the mousetrap. The piece shown is 2½ inches by 6 inches, but the size of the piece can vary, so just use what you have. Any type of wood will work, but for a contest balsa is the best choice, since it is very light. But using balsa may mean a trip to the hobby store.
Step 4: With an adult's help, use a handsaw to cut from the end to each side of the hole. You will be left with a ½-inch-wide, U-shaped cutout from one end.
Step 5: Use wood glue to secure the mousetrap to the wooden base you just created. Make sure the U extends past the end of the mousetrap. Let the glue dry for a few hours.
Step 6: Once the glue is dry, put a screw eye into the bottom of each corner of the wooden base.
Step 7: Cut your dowel a few inches longer than the width of your base wood block. Slide a faucet washer onto the dowel with the beveled side pointing out. Cut another axle out of the dowel for the front wheels. Set one piece aside.
Step 8: Have an adult put superglue on the beveled side of the washer.
Step 9: Before the glue dries, quickly slide a CD onto the dowel so that it is on the beveled side of the washer and center the washer in the hole.
Step 10: Slide another faucet washer onto the dowel with the flat side toward the CD. Press it onto the CD and make sure it is centered. Let the superglue dry for at least 5 minutes.
Step 11: Slide another washer on the axle with the beveled side toward the mousetrap and the flat side toward the CD wheel. Slide the wheel axle combination through the rear set of screw eyes. The rear of the car is the end with the U. Slide another faucet washer onto the other end of the axle with the bevel toward the mousetrap to secure the axle in place.
Step 12: It is easier to do this step before you put the other rear wheel on. Tie a 20-inch-long piece of fishing line or thread to the rear axle in the cut-out U. Use a cable tie, zip tie, or tape to secure your knot. The fishing line can just dangle while you finish the rest of the construction.
Step 13: Slide another washer onto the axle with the beveled side out. With adult help, superglue another rear wheel on the other end of the rear axle. Secure with another washer, with its flat side toward the wheel.
Step 14: Make sure the wheels are parallel to each other and straight up and down. Let the glue dry for at least 5 minutes before starting on the front axle.
Step 15: Repeat Steps 9 through 11 on the front axle. You may need to shorten the axle depending on the length of your wooden base. Set aside for at least 10 minutes to let all the glue dry before getting ready to launch your Cheese Wagon.
Step 16: Tie the free end of the fishing line or thread to the middle of the spring hammer on the mousetrap. You will probably want to secure the knot with tape or a cable tie.
Step 17: Pull the spring hammer toward the rear and slowly wind the fishing line or thread around the rear axle.
Step 18: Place the car on the floor and let the spring hammer go.
Additional Racecar Topics
You can increase friction on any wheels by adding rubber. You can do this easily with balloons. Blow up a balloon and let it deflate several times to stretch it out. Cut 4 slices across the balloon to create 4 large, circular straps. Stretch each piece of balloon around the edge of each CD.
Top Fuel is a long, sleek, rolling machine designed to travel over 50 feet.
Adult supervision required
Brass tube, 12 inches long
Long piece of wood, 1 inch wide (balsa is best)
Drill and bits
2 brass tubes or dowels with 3/16 diameters, 6 inches long
4 old CDs
Duct tape (optional)
Fishing line or thread
Step 1: Use needle-nose pliers to remove the staple securing the mousetrap's holding bar, if present.
Step 2: Remove the holding bar to reduce weight, if allowed under competition rules. Some contests may require the car to be launched using the catch and holding bar. If both are required by rules, skip to Step 4.
Step 3: Remove the catch as well.
Step 4: Use the needle-nose pliers to cut the spring hammer on one side of the square. Remove the short piece left and straighten out the long remaining piece.
Step 5: Lay your mousetrap and the long piece of brass tubing on the 1-inch-wide piece of balsa wood. Mark the length with a pencil and then cut 2 pieces to that length.
Step 6: Have an adult drill a ¼-inch hole in both boards, 1 inch from the end. Drill slowly in balsa wood because it is very light. These holes will hold the axles, so they need to be drilled at the same time, which will allow the axles to be perfectly parallel and perpendicular to the long side rails.
Step 7: At the end of each wooden rail, put 3 inches of wood glue along the narrow edge. This is the top of the rail.
Step 8: Place the mousetrap on the glue with the loose spring hammer pointing toward the long end of the rails. Make sure that the rails are at the edge of the mousetrap and that the rails are perfectly parallel. Let this glue dry for at least 24 hours before you put the axles through to complete the Top Fuel. You can work on the wheels and axles while the glue dries.
Step 9: Push one short brass tube through the center of a faucet washer. Repeat for the other brass tube. If you don't have a brass tube, 3/16-inch dowels will also work.
Step 10: Slide a faucet washer into the center hole of the CD. Many washers will fit very snugly and will not need superglue. If it fits snugly, you are done. If not, you will need to use a second washer to sandwich the CD, and possibly some superglue to hold the washers together.
Step 11: Slide the long brass tube onto the straight piece of the spring hammer on the mousetrap. Friction should hold it in place. If you don't have a tube, you can use a 12-inch-long piece of dowel — use duct tape to secure it to the spring hammer.
Step 12: Use needle-nose pliers to create a hook in the other end of the tube. If you used a dowel you can skip this step.
Step 13: Tie a long piece of fishing line or thread to the hook. If using a dowel, just tie it tightly to one end and secure with a small strip of duct tape.
Step 14: Use the needle-nose pliers to bend the hook over to further capture the fishing line or thread end.