Crash Test Dummies (uphill)

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

Parameters: The sled must be made of found, recycled, repurposed materials, not purchased or made from any kind of 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 an inclined table, and your sled will be pulled uphill towards the wall by a falling mass tied to your sled with a string. You must have a coffee stir stick attached vertically to your sled for the photo gates. You must have a copper wire loop at the very front of your sled for attachment of the string. You may start your sled at any point at least 50 cm from the wall.

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

Score = E • V / (m² • x²)

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

V = average velocity in meters per second, measured by photo gates attached to the wall.

m = mass of the sled (without the egg) in dag (decagrams, 10 grams)

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

Highest score will receive highest rank.

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

A fraction of a second before impact, the falling mass will hit the floor, and then your egg and sled will experience a dramatic impulse from the 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 sled that goes straight slides 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

Timeline: Day 1 Planning/Building, Day 2 Building, Day 3 Building, Day 4 Contest