Science Buddies: "Ask an Expert"

i have this project with deals with basic physics. the project states the you must power a car using a balloon to complete a race of 3 meters long. the balloon must physically power the car. For example: the air from a ballon drives the car forward. I need help with the best design that would complete the race in the least amount of time. if any one could give suggestions that would be great. thanks alot for your help

What have you considered?
What research have you done?
Are there any constraints?
What do you know about force and mass?
What sub-problems have you broken it down into?
What methods of converting air pressure in a balloon into force are you considering?

There are lot of Balloon cars here You can pick up one

http://www.basd.net/staff/kharman/Proje ... ctures.htm

Hi there,

First to deal with the power source (ie. ballon).
Use the Equation of Continuity principle to increase the speed your air/gas flows out of your ballon.
That is you want to constrict the size of the hole that the air/gas escapes from the ballon. That way the air/gas would come out at a faster speed than normal. The previous link the Expert gave shows some of this. One car uses a straw to make the hole smaller.
Try to see how small of a hole you can make and what effect it has on the (same) car.

Then to deal with the car.
Read this: http://en.wikipedia.org/wiki/Automotive_aerodynamics
Try to study which design reduces drag on the car.

Remember to chose a tire/wheel for the car that is not to smooth in surface as in the end what determines that your car move forward would be the friction between the tire/wheels and the ground.
If you could get a tire/wheel for your car that is made out of rubber I think that would be best.

Good luck !

[quote="Craig_Bridge"]What have you considered?
What research have you done?
Are there any constraints?
What do you know about force and mass?
What sub-problems have you broken it down into?
What methods of converting air pressure in a balloon into force are you considering?[/quote]

My group and I have considered the following: we want to have a large balloon so that there is a greater amount of air powering the car, we tried several designs already but we arent quite happy with any of them . Sadly :. but were gonna keep trying. The only constaraints really are: the car must move on its wheels and the sole source of propulsion must be provided by the balloon.As for reasearch well my group and I did reaserch about the best possible design shapes so that the car can have the least amount of wind resisitance and such. Also, we did reasearch about force and mass and how they work together proportionally to each other as stated in Newtons 2 law.

The sub problems that we currently we are facing is that we need to figure out hte best combinations of materials (for ecample: light enough but will still have some wiehgt tio make it stable enough. our other problem is we dont know what the sixe of the wheels should be. And this is propobly the biggest problem so far: how are wee going to have enough power to drive a car in a straight race track three meters long???

as for this Question 'What methods of converting air pressure in a balloon into force are you considering?'
i cant answer this question becuase as of now I am still thinking about the answer. However if there are any suggestions if possible that would be a greatful help.

[quote="ghariman"]Hi there,

First to deal with the power source (ie. ballon).
Use the Equation of Continuity principle to increase the speed your air/gas flows out of your ballon.
That is you want to constrict the size of the hole that the air/gas escapes from the ballon. That way the air/gas would come out at a faster speed than normal. The previous link the Expert gave shows some of this. One car uses a straw to make the hole smaller.
Try to see how small of a hole you can make and what effect it has on the (same) car.

Then to deal with the car.
Read this: http://en.wikipedia.org/wiki/Automotive_aerodynamics
Try to study which design reduces drag on the car.

Remember to chose a tire/wheel for the car that is not to smooth in surface as in the end what determines that your car move forward would be the friction between the tire/wheels and the ground.
If you could get a tire/wheel for your car that is made out of rubber I think that would be best.

Good luck ![/quote]


Thanks a lot for this idea we put in a straw adn other small tubing adn this made the car go considerably faster then before. As for the wheels we still have to get our hands on rubberized wheels, but when we do we will be sure to tuse your suggestions.

PS thanks alot for your help

For the car design you may want to look up links for the Pinewood Derby, which is the Cub Scouts competition where cars are all built to the same maximum weight, ostensibly out of the same block of wood.

As you can imagine, there are a multitude of different car designs, many of the better ones taking into account aerodynamics, weight distribution, friction, etc.

Weight distribution will not be terribly important to your balloon powered car (low total weight will be).

Aerodynamics (lessening drag) and friction (making the wheels as low friction as possible on their axles(ball bearings(?), but able to sufficiently grip the ground(rubber)) will be key factors in the success of your effort.

Inertial mass of the wheels (lighter wheels have to overcome less inertia to start rolling) will also make a big difference in the time your car takes to complete the course (think of a drag race with the car's wheels spinning -- when they are spinning, energy is being used, but no forward progress is being made).

As you can see from the above, even when keeping the balloon mechanism constant, there are many ways to improve the performance of your car.

Can this matter a lot? In a competition at a local school to build mouse-trap powered cars, the average car went about 3 feet. One kid's car went all the way across the high-school gym's floor hitting the opposite wall. We have no idea how far it would have gone if it had more room. Basically a massive performance improvement due to superb design.

Take this all step-by-step. Focus on the power plant (balloon), then the aerodynamics of the car, then the wheel/axle interface, then the wheels/tires themselves. All improvements on the individual components will add to the total performance of the car.

Good luck, and have lots of fun. Sounds like a great project.

Try to post a picture of the completed car if you can. I'm sure all the experts would love to see it.

[size=18][b][color=violet]Hey , thanx - you for all your help. I am finally done amd my group and i are just putting the last finishing touvches on our car and the lab report/ journal.[/color][/b][/size]

Post a picture of your car if you get the time. I'm sure we'd love to see your design.