Science Buddies: "Ask an Expert"

Hi guys, I'm doing a science fair project on "How fuel emissions effect the ozone layer?" I was wondering if you could help me find the independent, dependent and controlled variables for this topic please..I need to get this science fair project done in 3 days!

To answer that question you have to imagine that you were running a controlled experiment to see what effect car exhaust had on the ozone layer. You can't do that, of course, since we're effectively running that 'experiment' as a planet without a control, but imagine you were doing this in a lab.

The independent variable is what you're changing. What *one* thing would you change to see if car exhaust had an effect? This is actually a trick question so think about that carefully. The constants or controlled variables are the things that would be exactly the same between your experimental setup and the control. Finally, the dependent variable would be the effect. How do you determine how the ozone layer changed? That's pretty complicated as well, so think about that carefully also.

Here are a few websites to get you started: http://homeguides.sfgate.com/car-pollut ... 79358.html, http://www.conserve-energy-future.com/c ... e-hole.php

Good luck with your project. If you want to write back and bounce your answers off of us, we're happy to comment on them.

Howard

Hi, thanks for replying, the sites you recommended helped...so i think i kind of figured it out but just to make sure... do you think it would be alright if the independent variable is the ozone layer, the dependent variable is the amount of fuel emission and i don't know what to have as the controlled variable. It would be great if you helped me out. Thanks.

The thing you want to measure is the dependent variable. Let's say I wanted to know how many licks it takes to get to center of a Tootsie Roll pop. The dependent variable is the distance to the center - when I get to 0, I know I've achieved it. The indeoendent variable is the number of licks. As I lick the pop, more of the candy dissolves the distance from my tongue to the center gets closer and eventually reaches zero. The constants? In my experiment they would be how wet my tongue was, how hard I pressed the pop to my tongue, and not biting the candy off.

In your controlled version of this global 'experiment', what are you trying to measure? The thickness of the ozone layer? It's ability to block UV? The number of measured holes? One of those or perhaps something else is what you're trying to measure and that would make it the dependent variable. Since you're asking about the effect of car exhaust, what would you then say is the independent variable? What would you manipulate to see an effect? What other factors should you keep constant the whole time to make sure that your manipulated variable is really responsible for the effect? I'm sorry to not just answer your question but we don't do your homework here for you.

You picked a really complicated topic which can be difficult to pick out single variables. Pretend you were doing this in a classroom lab with a sealed fishtank full of ozone and a tiny car with a real engine. Does that help?

Howard