Do gases weigh anything?

This week in Science, we have investigated whether or not gas weighs anything.  Some of us thought that because gas was invisible that it wouldn't have any weight to it, others thought that because it is a type of matter that it must have a weight.

To test our scientific reasoning, we got a range of fizzy drinks, in cans, which we compared before and after they were shaken.

We had a few issues to address first:

1. Would the balance scales pick up any tiny changes in weight?
2. Would the weight of the can change if it was closed, and the gas couldn't escape?
3. How would we be able to compare the weight before and after shaking, if we were just using balance scales?

We had to make sure our balance scales were balanced and ready for accurate measuring. We also decided to test the cans closed and opened; this way we could see if the gas escaping had an impact on the weight of the can. We used a control can, which had a sticker and had to stay the same, and this way we could compare the shaken can to the control can.

Equipment:

• balance scales
• a variety of fizzy drinks in cans x 2 of each

Method:

First of all, we set the scales up and made sure they were balanced, and then we weighed the cans to check they were the same.

After that, we shook one of the cans, and then we remeasured and compared both cans again, using the balance scale.

Immediately, we removed the can and shook it again. We repeated our measuring and recorded our results.

Finally, we opened the can, very slightly, so that some of the gasses would escape. We then swirled the cans to release more of the gas. As we did this, we listened and could hear the gas coming out of the can. We measured again and took our final notes.

Results:

We found that the can which had been shaken, weighed less at the end of the experiment. This proves that gas has weight because as it escaped from the can, the can became lighter.