☯ Concept Cartoons ☯
Table of Contents
1 Chemistry Density 5 - Does helium have a weight?
Have you talked about your ideas? Do you agree with any of the characters or do you think something different? Do you all have the same ideas? Here are some ways of finding out more. It is difficult to weigh gas in a floating balloon. You can find out whether air has mass and weighs something using balloons full of air. Put one on each end of a lever balance and carefully pierce one through a piece of tape stuck on the balloon. Observe what happens and talk about why. However you can’t weigh helium like this. Research on the internet to find the weight of a helium cylinder when it is full and when it is empty. How will the weight of the helium gas cylinder change as it is used to fill balloons?
Here’s what a scientist might say. Did you find any evidence to support or justify these ideas? Are there any questions that you still need to answer? All gases have mass, and gravity pulls on them so they must have weight. If you put helium in a balloon then it must get heavier. So why does it float? If you push something that floats so it goes underwater, it pushes some water out of the way and the water pushes back. We call this force buoyancy, and it pushes the object back towards the surface. Air pushes on objects as well. Helium is a very light gas that is much less dense than air. A tiny mass of it takes up a lot of space. A balloon filled with helium gas does get heavier but it also becomes less dense than the air around it. The air pushes on the balloon and makes a buoyancy that is big enough to make the balloon float upwards. Create an annotated drawing to show why a helium-filled balloon floats in air and an air-filled balloon doesn’t.