Olympic Engineering: Bobsled Challenge
Get ready for the Winter Olympics by designing, building, and testing your own mini-bobsled to learn about the science behind this speedy sport!
What you will need:
- Cardboard tubes (from toilet paper or paper towel rolls)
- Plastic drinking straws
- Washers, nuts, and/or pennies (for weight)
- Scrap pieces of fabric
- Aluminum foil
- Rubber bands
- Paper clips
- Pipe cleaners
- Craft sticks
- Markers or paint
- Long flat piece of cardboard
- Smaller pieces of cardboard
Here’s what to do:
- Design your track: Find an inclined plane or ramp you can use as a bobsled track or make one yourself. Use a long (at least 3 feet), flat piece of cardboard propped against a chair to make a ramp. You can also use smaller pieces of cardboard to make walls on the track to keep your sled from falling off the side if you’d like.With a parent, you can also take this activity to a park and use the playground slide as your bobsled track!
- Design your sled: Gather the materials you have available. Feel free to include more materials if you have them. With the materials you have, pick a base and two skis (called runners on a bobsled) to carry your sled. A first design to try: Cut a cardboard tube in half lengthwise to leave two open halves. Use one half of the tube as your bobsled base. Glue or tape two drinking straws along the outside of the cardboard tube like skis where the tube will touch the track. These are your runners.
- Now you can try testing your simple bobsled on your track. Use the stopwatch to time how long it takes for your bobsled to reach the bottom of the track. What do you think could make your bobsled faster?
- Modify your bobsled to make it faster. As you modify your bobsled, we recommend only making one change at a time. Make a change, then test your bobsled on the track and write down the time. Repeat until you make the fastest possible bobsled.
Some ideas to try: Try taping some pennies or other small weights to the inside of your bobsled. Does it matter if you add weight to the front or back of the bobsled? What happens if you add a nose to the front of your bobsled? Does it go faster or slower down the track? Does your bobsled get faster if you add an extra runner to the bottom? Where would you put it? What happens if you add a different material to the bottom of the bobsled or the runners? Can you find a material that makes your sled faster than the plastic and cardboard? Try materials like aluminum foil, pipe cleaners, fabric, rubber bands, or craft sticks.
Engineers use a process like this all the time! They plan an experiment or design an object, test it, then change one thing (or variable) at a time and test again. This is called the Engineering Design Process, and it helps the engineers to track their changes so they can figure out which variable are important for improvements and which are not.
- Once you have a final or favorite design, decorate your bobsled to represent your personal Olympic team! Do you decorations change the weight or shape of your bobsled? Does that affect the time it takes to finish the track?
- Things to think about: Which design goes the fastest? Did you find any materials that make your bobsled go slower? Why do you think that happens?
Take it further:
- Design a new bobsled with a new base like craft sticks or cardboard. Does the base material matter? Try a new runner material too. Does the runner material matter? Which combination of materials make the fastest bobsled without added weight?
- What is the ideal amount of added weight for your bobsled on your track? Do you think this amount of weight is ideal for all tracks?
Change the angle of your ramp and test your bobsled again. Is it still fast? Is it possible to make your bobsled too heavy?
If you make your track steeper, you are increasing the potential energy that can be turn into motion (kinetic) energy when you release your bobsled. If you make your track less steep, you decrease the potential energy and therefore, the kinetic energy, so your sled should be slower.
- Quickly rub your hands together. Do you feel any heat? That heat is caused by motion energy (kinetic energy) being converted into heat through friction. This happens when two things rub against each other, like your bobsled running along the track. The energy lost to heat is not used for motion, so your sled gets slower as friction increases.
Can you find any materials to add to the bottom of your bobsled that increases friction and slows your bobsled down? Does it matter how much of that material touches the track? How slow can you make your bobsled without it being at a standstill?
- What happens if you design and add two people to your bobsled? You can use any of your materials. Does the extra weight make your sled faster or slower? Does the shape of your bobsled people matter? Why do you think bobsled athletes duck down into the sled?
What’s going on?
Real bobsleds, like those used in the Olympics, can weight 280 to 460 pounds by themselves, and have teams of two or four people who drive them down the track. The world’s steepest bobsled track is 4757 feet long and has a 500 foot elevation change from start to finish; this can generate speeds up to 95 miles per hour! Plus, bobsled tracks are not straight like the one we used in this activity, so the athletes have to learn to steer their speedy bobsled around turns and curves on ice!
At the top of the track, the bobsleds have high potential energy and no kinetic energy (because they aren’t moving). As the athletes push the slide down the track and jump in, they start the conversion of the potential energy into kinetic energy. When all the athletes jump into bobsled, they now rely on their driver, principles of physics like gravity, friction, and drag, and a well-engineered sled to help them get down the track fastest!
Drag is also known as air resistance and is a type of friction. Remember how we discovered friction by rubbing our hands together? Then, we learned that any two materials rubbing against each other experience friction; air is one of those materials. When you walk around, you rub against air and experience some air resistance, although you probably don’t feel it all the time. In a bobsled going really fast, the drag becomes very noticeable and can slow a bobsled down significantly. The larger the surface area of an object hitting the air and the faster the object is moving through the air, the more drag the object will experience. To reduce drag, teams design and test different sled shapes and practice ducking down inside the sled because the more sleek and smooth the sled appears to the air, the less drag it will experience.
Athletes and their bobsled engineers also work to reduce other kinds of friction. The athletes have to practice pushing the sled and jumping in while keeping the sled straight because any side to side movement will increase friction and slow down their bobsled. The driver has to be very precise and use his team members to help shift weight in the sled to make smooth turns. If the sled touches a wall of the track there will be friction.
Gravity is a constant force, so all of the bobsled teams will experience the same acceleration due to gravity, but they can all experience different forces of drag and friction. At some point, gravity will equal the drag and friction forces, but in the opposite direction, this is known as terminal velocity. The bobsled cannot go any faster. To have the fastest run, bobsled teams don’t want to reach terminal velocity, they want to keep accelerating as long as possible, so they want to reduce drag and friction and be at the maximum weight allowed in the competition. There’s a lot of science and engineering know-how needed to win an Olympic medal in bobsled!