Science Buddies: "Ask an Expert"

I need to design and build a mechanical device that will transports a standard glass Christmas tree ornament a distance of 8 meters along a straight track as fast as possible and crash into an end barrier. The car must be a single unit 1m x 1m x 0.75m. A maximum of ten Joules is allowed for moving the car. All energy must come from falling mass(es) not to exceed 2.75Kg. The ornament must be in front of the device and extend 2cm in front of the most forward part of the divice as the ornament must hit the barrier first. The device must have a flat, rigid, unpadde backstop behind the ornament. the rounded end of the ornament must rest against the rigid backstop as no harness devices may be used to cradle the ornament.

A barrier must be built that will fit into a 1m x 0.15m x 0.10 m box, the barrier must be constructed so that the ornament is in contact with the barrier from the beginning to the end of the collision.

Any ideas is appreciated
Nemo

Hi Nemo --

The problem description you've been given sounds more like something from a creative problem solving tournament (e.g., Odyssey of the Mind, Destination Imagination, etc.) rather than a science project. Can you elaborate what this is for? This most certainly doesn't sound like a scientific investigation, which is what these forums are primarily intended for.

Besides, I'm not entirely sure what you're asking. Are you asking for someone to design your solution for you? It would seem that the whole purpose of this exercise would be for you to use your creativity and imagination to design it yourself (or with your team).

--Rajeev

Is the goal to keep the orament from breaking? In other words, is the major component of this design to create a shock absorbing barrier device? If you want some help and ideas from us, you need to tell us a bit more about the orientation of the barrier box container. Which dimension is along the axis of acceleration/deacceleration? Which dimension is the height, and which is the width?

Does the vehicle have to be precisely 1m x 1m x 0.75 m? What is the height, the length along the axis of motion, and the width perpendicular to the axis of motion?

Since the impact force that must be absorbed is 0.5 m v**2 (one half times the mass times the terminal velocity squared), if your goal is to not break the ornament, you will want to minimize the mass of the vehicle and you might want to NOT go for the highest velocity possible.

You likely are going to want to use a variety of densities of shock absorbing materials. You will want lower density materials to start with so that it will deform around the ornament and equalize the forces and then you will want increasing density materials so that the sled contacts more rigid materials to stop the sled quickly before the pressure on the ornament exceeds the differential breakage point somewhere around the circumference.

This sounds like an interesting science class challenge project. It would be difficult to turn this into a Science Fair Project; however, much of the design research and experimental methods can be used to come up with a solution. Hopefully, you have a source of inexpensive glass ornaments. I'd also suggest using something like a few layers of some plastic cling wrap to protect your barrier and sled from accumulating glass fragments. You discard the plastic wrap after an unsuccessful run as part of the clean up.

One way to approach the experiment is to start out with lower velocities and work your way up to your goal.