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panag10
mousetrap_car_basics.pptMASME:
August 1-3, 2008
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What is a Mousetrap Car?
- A vehicle powered by the spring device of a mousetrap
- The mousetrap acts as a third-class lever
fulcrum
applied force
resultant force (load)
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What is a Mousetrap Car?
- How does the power source work?
- The spring propels the hammer, which causes an enormous release of energy
- The hammer is connected to a string that is wound around the drive axle
- The string unwinds as the hammer snaps– making the car roll!
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
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Scientific Concepts
- Potential Energy: energy that is stored within an object, not in motion but capable of becoming active
- You have stored potential energy (in the spring) when your mousetrap is set and ready to be released
- Kinetic Energy: energy that a body possesses as a result of its motion
- Potential energy becomes kinetic energy as the mousetrap car begins to move
- Some of this energy goes to friction– the rest makes your car go!
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Scientific Concepts
- Force: an action that causes a mass to accelerate
- To change the motion of your mousetrap car, you must apply a force
- To increase the acceleration of you car, you must increase the force or decrease the mass (Newton’s Second Law)
- Friction: the force that opposes the relative motion of two surfaces in contact
- Friction will slow– and eventually stop– your mousetrap car
- Friction occurs between the wheels and the floor and between the axle and the chassis
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Scientific Concepts
- Torque: can informally be thought of as "rotational force" or "angular force" that causes a change in rotational motion
- In your mousetrap car, the snapper arm applies a force to the drive axle through the pulling string. This in turn causes a torque to be produced around the drive axle.
- Power: the rate at which work is done or energy is used
- In a mousetrap car, the same amount of energy is used regardless of its speed – only the rate of use changes
- For distance, you want to use energy slowly; for speed, you want to use it more quickly
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
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Construction Hints
- When building a mousetrap car, there are a number of variables to consider
- Weight of the car
- Placement of the mousetrap
- Length of the snapper arm and the string
- Size and type of wheels
- Wheel-to-axle ratio
- Your design decisions will depend on the goal of your car: distance or power
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Weight of the Car
- For all cars, you want to build the lightest possible vehicle
- Lighter vehicles will require less force to begin moving and will experience less friction than heavier vehicles
- However, if your car is too light, it will not have enough traction
- This will cause the wheels will spin out as soon as the trap is released
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Length of the Snapper Arm and the String
- Long snapper arms and short snapper arms release the same amount of energy
- The difference lies in the rate at which the energy is released (power output)
- For distance cars, try a long arm. Longer arms will provide less force, but more distance.
- With a longer arm, more string will be pulled off the axle
- This causes the wheels to turn more times and allows the vehicle to cover more distance
- For power cars, try a shorter arm. Shorter arms will provide more force and power output, but less distance.
- These cars need the power to get up the ramp!
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
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Length of the Snapper Arm and the String (cont.)
- For all cars, the lever arm should just reach the drive axle when it’s in the ready position
- When the string is wound, the place where the string is attached to the snapper arm should be above the drive axle
- This will maximize your torque as your car takes off (maximum torque occurs when your lever arm and string form a 90° angle)
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
Correct length
Too long!
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Length of the Snapper Arm and the String (cont.)
- The string length should be a little shorter than the distance from the lever arm to the drive axle when the trap is in the relaxed position
- This will allow the string to release from the hook– and prevent tangles!
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
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Placement of the Mousetrap
- For distance cars, place the trap farther from the drive axle
- You’ll sacrifice pulling force, but get more distance
- For power cars, place the trap closer to the drive axle
- You’ll sacrifice distance, but get more pulling force
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
Drive axle
Distance placement
Power placement
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- For distance cars, larger wheels will cover more distance per rotation than smaller wheels
- For power cars, make sure your wheels have good traction so they don’t slip
- You can increase traction by covering the edges of the wheel with a rubber band or the middle of a balloon
Size and Type of Wheels
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
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Wheel-to-Axle Ratio
- For distance cars, a large wheel-to-axle ratio is best
- A large wheel with a small axle will cover more distance each time the axle turns
- For power vehicles, a smaller wheel-to-axle ratio is best
- Increasing the size of the axle will decrease the wheel-to-axle ratio
- This will increase the torque and give you more pulling force for every turn of the wheel
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
(from Doc Fizzix’s Mousetrap Powered Cars & Boats)
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