gloria9
Posts: 2
Joined: Tue Jan 12, 2016 6:03 pm
Occupation: Teacher

### Making the Balloon-Powered Car Challenge work as a scientific method project

Is changing the wheel size a good independent variable? Or should their be more than two sizes? Or if it is going to be tested three times for each wheel size so two sizes is enough? OR is it using the same car,but changing out the two sizes of wheels and testing 3 times each?

dcnick96
Moderator
Posts: 507
Joined: Wed Jul 25, 2007 7:59 pm

### Re: Making the Balloon-Powered Car Challenge work as a scientific method project

Hi, Gloria.

This sounds like a fun project! A good independent variable is any part of the car you think by changing it will affect the outcome of the travel / speed of the car. In your case, I think wheel size is a good option. A good test design is one that:

1. Changes only one thing at a time. If you change the size of the wheel, make sure nothing else about the wheel or car changes: materiel, tread type, amount of air in your balloon, car shape, car size, etc. If you change these, as well, you don't know which change affected the outcome. Changing two variables at a time is called confounding. Avoid doing this. For example, If you do a small size tire made of rubber and larger size tire made of metal, you are changing two things at once; and if you find a difference, was it due to tire size or material?

2. Always collects at least 3 samples for each set of unique conditions. So, in your case, you will want to test at least 3 times for each tire size. You can do an unlimited number of any of your independent variables. A good design consists or prior research to justify the changes in your variable. In your case of tire size, are there articles you can find or math you can do to help determine what size tires would work best for your car?

I hope this helps. Feel free to write back with questions. Good luck!
Deana
Deana