Science at Home Videos

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: And this is a 'Science at Home' edition of Frostbite Theater that you can do along with us! Just download the worksheet from our website, or you can just use a piece of paper to write your data.

"What's the experiment?" you ask? We're going to be identifying three mystery materials by determining their densities.

Steve: Now, density is a number that tells us how much matter is crammed into a certain amount of space. A bowling ball is denser than a balloon, for example. And, that's not because a bowling ball is heavier than a balloon. Just because something's heavy doesn't mean that it's dense. Even though I can pick up this penny, its denser than an aircraft carrier. We know this because aircraft carriers float on water, but pennies sink.

Joanna: In order to calculate an object's density, we need to know its mass and its volume.

Steve: Mass is easy. Ideally, we'd use a balance. But, instead, we're going to use an electronic scale. And, as long as we don't do anything weird, like use it in an elevator or on the moon, it'll give us reasonable values for the mass.

Joanna: For volume, we're going to use the water displacement method. If you have a container of water and you put an object in it, the water level rises. That's because the object makes room for itself by pushing the water out of the way. The amount of water that's displaced is equal to the volume of the object that's in the water. If we submerge the entire object, we'll be able to measure the total volume.

Steve: Let's work though a quick example.

I have a bunch of pennies. If I put 'em on the scale, it says they have a mass of... 50.1 grams. This graduated cylinder contains... 51 milliliters of water. If I put the pennies in... And then get rid of the bubbles... The reading is now 58 milliliters.

So, adding the pennies added 7 milliliters to the volume. Which means the pennies have a volume of 7 milliliters. And, we'll make life easier on ourself and convert milliliters to cubic centimeters, which is super easy, barely an inconvenience, since 1 milliliter is equal to 1 cubic centimeter. Thanks metric system!

Joanna: Now that we know the mass and the volume, we can calculate the density of the pennies. To do that, we just have to divide the mass of the pennies by the volume of the pennies, which works out to be about 7.2 grams per cubic centimeter. If we check our handy density chart, we can see that 7.2 is a good match for zinc.

Steve: "Wait a second!" we hear you say. "Pennies are copper! 7.2 grams per cubic centimeter is way too low!"

Joanna: To which we say "Pennies used to be copper. They started making them out of zinc in 1982."

Steve: And all of these are newer pennies. So, yeah, they're mostly zinc.

Joanna: So, if you're ready, we'll give you two samples of the three mystery materials. Measure the mass and volume and see if you can determine what it is based on the density. Feel free to pause the video if you need extra time to make and record your measurements!

Ready? Here we go!

Joanna: What do you think that mystery materials are? Let us know what you came up with in the comments!

Steve: One more thing before we go. You may have noticed that, while the scale is fairly precise, this thing isn't. And, sometimes, the water doesn't even look level. Happily, the materials have simple shapes, so we can use a more accurate and precise measuring instrument, and a little geometry, to calculate the volume. Here's all the relevant information if you want to have a try at that.

Joanna: Thanks for watching!

I hope you'll join us again soon for another experiment!

Steve: Okay! Thank you Joanna! See ya' later!

Joanna: See you Alfie!

Steve: Alfie? What's weird...

Must mean something...

Hummm...