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MESA Mouse Trap Powered Cars. Basic Competition Rules. Greatest distance travelled without leaving 6-foot wide track Zero alteration of mousetrap do not take the spring apart do not drill holes in or paint the trap except screw attachment holes
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Basic Competition Rules • Greatest distance travelled without leaving 6-foot wide track • Zero alteration of mousetrap • do not take the spring apart • do not drill holes in or paint the trap • except screw attachment holes • trap lock must be working and sprung with a pencil or similar object
Physics of Mousetrap Car • Friction forces • Drag • Acceleration • Torque • Momentum
Friction • Rubbing forces on moving parts • Effect: slows car and prevents maximum distance • Caused by: • excess wheel to road contact • poor wheel alignment • various parts rubbing when in motion
Wheel to road contact • Skinny wheels incur less friction than wide wheels • “total surface area” of all wheels
Skinny Wheels Skinny Wheels work best
Poor Wheel Alignment • Axles should be aligned perpendicular to car; if not, • Cars veers to right of left • Excess friction between front and back axles
Moving parts rubbing • Axles rubbing on car body • Axles rubbing on mounting screws or holes • Lever arm against body • String against body or axle • Wheels against body
Drag • Anything that slows or stops the car • Such as: • Friction • Parts hanging off car • Wide lever arm or wheels
Acceleration • Getting the car moving with trap • Strongest possible residual strength in mouse trap • Optimum lever-arm to car length ratio (also consider trap position) • Too long or short of lever arm reduces potential acceleration • Friction reduces acceleration
Torque • Getting power to the wheels: ability to get car moving • Too much torque = less distance (wheel spin) • Too little torque = car will not move • Torque altered by changing power arm angle to axle • Firm string to axle attachment
Momentum • Keeping the car moving after acceleration phase • less friction = greater distance • the heavier the car, the greater the momentum
Long Cars: less torque less speed less momentum much longer acceleration period Short Cars: more torque greater speed more momentum shorter acceleration period Long vs Short Car
Maximizing distance • longest power arc (arm length) • ideal torque (mousetrap position) • largest wheel diameter (greatest distance per wheel revolution) • smallest axle diameter (most revolutions per inch of string)
Long Arm 2009
Large Diameter wheels Small Diameter Axles
Comes Down to Car with • trap not modified • least amount of friction • maximizes design acceleration capability • finds ideal torque for design • most possible momentum • stays on the track
Summary: Building Tips • Large drive wheels • Small drive axle • Do not tie string to axle • Axles perpendicular to car • Correct mouse trap relation to car length