Crash Test Dummies

Challenge: To design a “car” that will safely carry an egg as fast as possible into a collision with a brick wall.

Parameters: The car must be made of found, recycled, repurposed materials, not purchased or made from any kind of car-related toy or device. It cannot be larger than 30 cm long, 15 cm wide, and 15 cm tall. It cannot be wider than it is long. The top half of the egg must be visible at all times, and can only be restrained by a “seat belt” made from 30 cm of string provided by Mr. Jamieson for that purpose. The “seat belt” cannot be attached in any way directly to the egg. The track will be a long ramp with side-walls with a curved transition to the floor just one metre before the brick wall. You may start your car at any point at least one metre from the bottom of the ramp.

Scoring: Your system will be scored based on the survival of the egg, the speed of the car, the directional stability, and the mass and dimensions of the car.

Score = E • D • V^2 / (m • x)

E = egg health, with 3 for undamaged, 2 for cracked but not leaking, 1 for leaking.

D = directional stability, with 3 for hitting within the centre target, 2 for overlapping that mark, and 1 for being outside that mark.

V = velocity in meters per second, measured by video analysis at the bottom of the ramp.

m = mass of the car (with the 60 g egg) in hg (hectograms, 100 grams)

x = length of the car in dm (decimeters, 10 cm)

Highest score will receive highest rank.

Physics: The higher you start your car on the ramp, the more potential energy you have. (∆E_p = mg∆h) The car will transform some of that energy into kinetic energy, (E_k = 0.5mv²), but also some will be lost due to friction during the run (W = Fd).

During the turn from ramp to floor, there will be a considerable upward impulse experienced by the car (∆p = m∆v), but that will be nothing compared to the impulse experienced at the collision with the brick wall (∆p = F∆t = m∆v). Total kinetic energy is not conserved during the collision because the collision is not elastic, which is actually a good thing. See if you can explain why.

Extensions: Your design should mimic the features in our vehicles, like air bags, crumple zones, etc. Think of the egg as you in your car.

Help/Hints: You want a small, light vehicle that goes straight and rolls with very little friction. You need a “seatbelt” that will keep the egg from popping up out of the seat, not just horizontally stable. You should put padding around the egg that “crushes” as opposed to “springs”.

Quiz Topics: Energy and Momentum

Online Text: 7.1 - 7.7, 8.1 - 8.6