Challenge: How far can you make your racer drive?
Build a gravity-powered vehicle. Place it at the top of the ramp and see how far you can make it go. How can you change it to make it go further?
Rules: We encourage you to try creative designs solutions to the challenge. Here are the few aspects your design must have:
- At least 2 wheels (max 8 wheels)
- Minimum of two axles
- Chassis must be at least 4 sq in
Bonus points: Can you make a vehicle with an odd number of wheels? Can you have two different sized wheels on one axle?
- ~4"x5" Corrugated cardboard or Sintra
- 2 - 6 Kelvin wheels preferably a mix of the following
- 2 Plastic straws
- 2 Bamboo kitchen skewers
- Masking tape
- Wire cutters (for cutting the bamboo skewers)
- Tape measure for noting progress (100')
- Marker to show the best drive
- Coping Saws (optional - for cutting cardboard)
- Hot Glue Guns (optional)
- Ramp - Cardboard ramp to go with the cardboard city look? Otherwise, a Sintra ramp. Should we use one lane of the 2 story slide?
- Construct and set up ramp
- Mark distances from the ramp in 1' increments with tape
- Lay out supplies
- Create a model racer
- (Optional) Run all skewers through the band saw to remove pointy ends
What visitors do
- Tape your straws (bearing) on the bottom of the cardboard or Sintra chassis
- One towards the front
- One towards the back
- Make sure the straws are parallel
- Remove the pointy ends of the skewers
- Put a wheel on the end of a skewer (axle)
- Run the axle through a straw
- Place a wheel on the other end of the axle
- Add another axle and two wheels to the other straw
- Place your racer at the top of the ramp and let go
What presenters do
- Ask visitors the Thinking Questions
- Place the marker at the longest drive
- Announce when a new record is set to encourage mild competition
- Ensure rapid use of the ramp, this can be a bottleneck
- Encourage participants to keep trying, "One and Done" is not enough
- Congratulate participants when they set new personal records
- How far did your racer go? Can you make it go farther?
- Did it drive in a straight line? Why?
- Why does the racer stop?
- Can you reduce the friction or rubbing between the wheels and the chassis?
- What happens if you release the racer lower on the ramp?
Most cars get their energy from gasoline or electricity. These Downhill Racers are powered by gravity. By lifting the racer to the top of the ramp, you give the racer gravitational potential energy. You can think about potential energy as the energy you had to put in to lift the object up. When the racer is released, the potential energy is converted to kinetic energy as the racer rolls down the ramp. The higher it started on the ramp (more potential energy), the more it can accelerate on the way down (more kinetic energy). It will continue to go faster until it gets to the bottom of the ramp. Then, with no more potential energy to convert, it will stop accelerating and coast. How far it can coast is mostly determined by two factors: alignment and friction.
Watch how the racer drives. Does it steer to one side or the other? This is due to the alignment of the axles. If the axles are parallel, the racers should go straight. If one of the axles is turned slightly, this will cause the racer to steer in that direction. This is just like when riding a bike. When the wheels are both pointed in the same direction, the bike goes straight, but when they point in different directions, the bike turns. If your racer turns, then it won't travel as far forward.
What ultimately brings the racer to a stop is friction. Friction slows down moving objects when they rub against another object. The kinetic energy is turn into (a small amount of) heat. There are several places on the racer that create friction. There is friction where the wheel touches the ground and what surface it's driving on greatly influences how much friction there is. Driving across a polished concrete floor has less friction than carpet which is why the racer can go farther on concrete. There is also friction between the axle and the bearing (straw). With some racer designs, the wheels rub against the chassis causing more friction. Finding ways to reduce the friction will allow your racer to go farther.
Safety Policies and Procedures
- Large shop tools - All large shop tools (band saw, drill press, etc) will be turned off at the breaker to prevent them from being accidentally activated
- Hand tools - All hand tools (except scissors, wire cutters, coping saws and glue guns) will be put away to discourage use
- Tape measure - Distances from the end of the ramp will be measured before the activity begins and will be marked on the floor with masking tape. The tape measure will be put away before the start to prevent tripping on it
- Any children under 12 will be encouraged to work with a parent and children under 8 will be required to work with an adult
- Tools used:
- Scissors - Student scissors will be used
- Wire cutters - Only small wire cutters will be available
- Coping saws - Fine toothed blades will be used
- Hot glue guns - We will use low-melt "mini" hot glue guns to reduce the likelihood of burns
- Bamboo skewers - The points of the bamboo skewer will be removed
- Ramp - The ramp will be positioned away from the work area, in an open space to reduce trip hazards
- Running - Walking will be encouraged to reduce trip hazards