Air Has Weight Concept Cartoon

This cartoon was developed to assess students' ability to:

• Explain that air has weight and is matter and, therefore, makes the ball heavier; this requires that they distinguish the objective weight of materials from their felt weight (air weighs something because it is matter from air weighs nothing at all because I don't feel it in my hand) and the absolute weight of a object from its density or heaviness for size.

This cartoon is typically used after Investigation 13, Is air matter?

Things to look for in student responses

Do students realize that an object's weight increases when air is added?

• Some students may agree erroneously with Tomas that air may make objects feel lighter because they are less dense or less heavy for size or because air has intrinsic lightness (i.e., adding air makes things lighter). These students may be confusing weight with density. Those who disagree may point out that air is matter, matter has weight, so if you add air, you are adding weight to the deflated ball.
• Others may agree with Leila, who points out that if you add air to the leather the weight will increase, because air is matter and all matter has weight. Students who have observed that when air is added to a balloon the weight increases (albeit slightly because air has a very low density) may use this as further evidence for agreeing with Leila. These students are giving evidence of moving away from thinking of weight as felt weight to weight as linked to amount of matter and measured on a balance scale.
• It's not unusual for students to think that air doesn't weigh anything and so agree with Fern. These students may say that they can't feel air in their hand, giving evidence that they are thinking about felt weight rather than objective weight. Students who have observed that when air is added to a balloon the weight increases (albeit slightly because air has a very low density) may use this evidence to disagree with Fern.