What Weird Al Can Teach Your Students About Mass, Weight, and Density
The difference between mass, weight, and density can be blurry in a student’s mind. In fact, to the same question asked in class, different students will give all three of those terms. Here is a funny little video clip that I use to distinguish those terms. Added bonus, it stars Weird Al Yancovic.
Distinguish Mass and Weight
Start the clip at 2:30. Let it run until 3:30 when he is sprinkling the sand. Then I ask the question, “What is he doing?”
The kids generally know the idea that he is trying to swap the bag for the idol. So to make them put a term to what they are seeing I ask them, “Why is sprinkling some of the sand?”
This is where they prove the challenge in mass, weight, and density. Some will say he is adjusting the mass, others adjusting the weight, and a few will say the density. This is where I try to distinguish mass from weight.
I ask why he was hefting the bag. Obviously, he is trying to determine how much matter there is in the statue and how much matter there is in the statue. The amount of matter in an object is its mass.
But why was he bouncing it up and down like that? It was so he could feel the matter interacting with gravity. The interaction of matter with gravity is called weight. So on Earth, mass and weight will always be directly proportional. Then I ask a challenging question.
What is the only way to decrease the weight without changing the mass? After some thinking, someone will generally say, change the gravity.
And how do you change gravity? You have to change your location. If Weird Al took that bag of sand to space, would its mass change? No. But would its weight change? Yes!
This line of questions generally helps students to see that there is a difference between mass and weight, but if you stay on Earth, those two terms are blended in common language. And for good reason.
Identify density
Play the video to 3:51 when Weird Al gets a giant rock dropped on his head. I like to play it a couple seconds past, then play it again and try to stop it right when the boulder is hitting his head. It gives the kids a laugh.
Then I ask a question that seems so obvious. Is that a real rock?
The obvious answer is no. Despite Weird Al’s amazing curly hair, it is not enough to protect him from a rock that size.
Is it the shape of a rock? Yes.
Is it the color of a rock? Yes
Is it the volume of a rock? Yes
Is it the mass of a rock? No.
The difference, then, is that the movie set rock had the same volume but not the same mass. And the ratio of mass to volume is density. Depending on the level that you want to teach properties, this is also where I go into intensive versus extensive properties with my honors kids. Density is an intensive property that gives definition to that material. Therefore, since the movie set rock had a different density than a real rock, we can confirm that they are not the same material.
The final line of questions leads students to start to compare densities. I ask if the movie set rock would float in water. The kids all say yes. But when I ask why, their answers tend away from density. They will say that because it is made of Styrofoam, and Styrofoam floats, then the rock will float. I direct them back to density. What must be true of the rock’s density for it to float? It must be less than water. A few of the students will remember from middle school that the density of water is 1 g/mL. So there must be less than 1 gram of rock in every mL of volume in order for the rock to float.
While this video clip and line of questions only take about 5 minutes, it is a great way distinguish the differences between mass, weight, and density. And with Weird Al as Indiana Jones, can you really go wrong?
Looking for more ways to engage your students? Check out Stoich Decks award-winning line of chemistry curriculum games. These games are designed to become part of your curriculum, not be added on as fluff. They are effective tools to help your students think in different ways. Check them out today.
Great illustration, but I definitely read the title as Weird ai the first time 😆