Rocket Cars...

[Ugouka]

Well, in my Honors Physics class, we just did a project with little hotwheels cars and rocket engines. Out objective was...well...to make them go as fast as possible. Our teacher basically gave us power tools and rocket engines to play with..because that couldn't go wrong or anything:rolleyes:. Anyway, I'm just curious if you guys have any suggestions on how to improve the design we used for our group.

 

Our track had to be 5 meters long and we used photogates to record our time. The gates were spread out 1 meter apart to give us the average speed. What my group did was this:

 

We took 5 meters of 2X4 wood and attached a wall to both ends of the track. At the start so the engine would have something to push against, and at the end so the rocket wouldn't fly into the other students and attack them. We attached 2 straws onto the sides of our hotwheels car and threaded wires through them and into the walls at the ends. When we tested it, we got a top speed of roughly 38 mph. It was a good time, but we felt it could have been better. Are there any suggestions for us to recreate this project with better results?

 

-Thanks. Tell me if you need more info about the project.

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Merged post follows:

Consecutive posts merged

Oh, by the way. I wasn't sure if this belonged in this section, or in the projects section. I ended up putting it in this one because I was asking for suggestions. Sorry if it's the wrong area.

Edited January 22, 2009 by Ugouka
Consecutive post/s merged.

[CaptainPanic]

Putting the rocket in a barrel (effectively making it a sort of gun) is much more effective than having a wall behind it. A wall really doesn't help much. You want to maximize the pressure behind the rocket, so that this pressure pushes the rocket forward. I am not sure how practical all of this is (since you have a car, not just a round rocket)...

 

And the other (obvious) improvement is to reduce weight as much as possible. the rocket will push with a certain force (F), and F = m*a. The acceleration (a) must me maximized, so weight (m) must be minimized.

[SH3RL0CK]

Think of where the energy losses will be:

 

1) air resistance: make the car as aerodynamic as possible.

 

2) track resistance: think about lubricating the track/wire. Maybe just use one wire instead of two.

[CaptainPanic]

Think of where the energy losses will be:

 

1) air resistance: make the car as aerodynamic as possible.

 

2) track resistance: think about lubricating the track/wire. Maybe just use one wire instead of two.

 

Indeed.

But you should also realize that making a car aerodynamic can add extra weight (if that means you have to add a point on the front and some different construction for making it lower or whatever).

 

Weight should not be sacrificed too much for aerodynamics if you're just aiming for a high acceleration.

 

Improving the track will not add any weight, so that's a great idea in any case.

[SH3RL0CK]

Indeed.

But you should also realize that making a car aerodynamic can add extra weight (if that means you have to add a point on the front and some different construction for making it lower or whatever).

 

Weight should not be sacrificed too much for aerodynamics if you're just aiming for a high acceleration.

 

Improving the track will not add any weight, so that's a great idea in any case.

 

Absolutely.

 

Another point to be sure of is to keep the rocket thrust properly aligned with the track. Otherwise, energy is wasted with the rocket trying to push the car "off track" instead of in the direction of the track.

[Ugouka]

Think of where the energy losses will be:

 

1) air resistance: make the car as aerodynamic as possible.

 

2) track resistance: think about lubricating the track/wire. Maybe just use one wire instead of two.

 

Well, we got a fairly small and streamlined car for the project, taking aerodynamics into account. We didn't want to add anything to increase this statistic, because of the added weight. The reason we used two wires was for stability. Other groups that used only one wire had their car flopping all over the place, greatly reducing their speed.

 

And as for Captain's idea for a tube, one group did try that, and had some difficulty. I see how that could improve it, but their wheels were unsteady on the curved surface, which is why we did not use it.