Air has mass. I know air has mass because when we weighed a balloon without air it weighed 2 grams, but when we weighed the balloon with air it weighed 2.7 grams this shows that the weight changed. We also can feel the air, when it is windy out you can feel the wind which is air. When I felt the balloon without air it felt rubbery and was able to stretch, When I felt the balloon with air it was more firm and couldn’t really stretch. Also, when you bounce a balloon it goes up than down which means it was affected by gravity and it kinda floated a little bit and after it dropped. This proves that air has mass because it weighed more which meant there was a substance inside that had a weight which meant it would have to have mass. Also when we blew air into the balloon and it expanded so that showed that the air had mass because it made the balloon and different shape. This proves why air has mass.