Magic of Density
Students will explore density by modifying the density of liquids, observing the density of different solids, and observing the density differences between objects that occupy the same volume by comparing varieties of pop. Mass over volume is the message!
What You Need
Part A - Egg Citing
- Two drinking glasses
- Two raw eggs
- Table salt
- Spoon
Part B - Ping Pong Tricks
- Large, clear container with lid
- Un-popped popping corn
- Ball bearing
- Ping pong ball
Part C - Pop Can Density
- 1 large basin filled with tap water (per group of 2 students)
- An assortment of different sodas in standard 12 oz cans - one diet soda and one regular soda can per group of 2 students.
- Salt (2 kg bag minimum per class)
- Tablespoons (1 per group)
Guide:
Safety Notes
Ensure you are familiar with Let's Talk Science's precautions with respect to safe outreach to youth.
What To Do
Part A - Egg Citing
Students will be placed into groups of 2 and obtain the materials necessary. Volunteer will guide students through procedure:
- Fill one of the drinking glasses almost to the top with plain tap water.
- Gently drop one of the eggs into the water-filled glass. (It sinks right to the bottom)
- Fill the second drinking glass half-full with water.
- Add four tablespoons of table salt to the water, and stir.
- Fill the rest of the cup with water, almost to the top.
- Gently place the second egg into the salt water solution (it floats).
Part B - Ping Pong Tricks
- Fill a large, clear container 3/4-full with un-popped popping corn.
- Here's the secret... push a ping pong ball down into the popping corn. Make sure that you cannot see the ping pong ball anymore.
- Set the ball bearing on top of the popping corn in the container and place the lid on the container.
- Conjure some magic and swirl the container.
- Like magic, the ball bearing is changed to a ping pong ball!
Part C - Pop Can Density
Students to get into groups of 2 and each group have a basin filled with tap water, 2 unopened pop cans; one regular and one diet. They should also have access to table salt.
- Ask students, “Will a can of regular soda float or sink in the bucket of water?” After gathering everyone’s answer, have students place the can of regular soda in the water and notice that it sinks to the bottom. If the can of regular soda floats, you might have an air bubble trapped under the bottom of the can.
- Have them pick up a can of diet soda and pose the same question. Be sure to guide them to point out the fact that the cans are exactly the same size and shape and contain the same amount of liquid (compare the number of milliliters… probably 355 mL). They should place the can of diet soda in the water. It floats! Wobble the can from side to side to show your audience that there are no bubbles trapped under the bottom. It still floats. Why? Guide discussion as to why one floats and the other sinks.
- Let your group experiment with different kinds of soda. Why do the diet sodas float and the regular soda cans sink, no matter the brand?
- Have students add approximately 1 tbsp salt to the water until 5 tbsp of added salt have been reached. Repeat the experiments with both cans using salt water.
Discovery
Part A - Egg Citing
The first egg sinks to the bottom of the glass of regular tap water. This is because a raw egg has a greater density than regular tap water. Essentially, the egg has more matter stuffed into a specific area (volume) than the same amount of water. When you add salt to the water, you increase the density. That is to say, the salt packs into the same volume of water. With enough salt added to the water, the density of the water is greater than the egg, allowing the egg to float.
Part B - Ping Pong Tricks
The secret is in the densities of the ball bearing and ping pong ball. If you compare the size, or volume, of the two spheres, you'll notice that they are very similar. However, if you compare the masses of the two spheres, there is a distinct difference. The ball bearing is much heavier than the ping pong ball. The two spheres share a comparable volume, but differ in mass. That means the balls have different densities. Density is the measure of how much "stuff" is in a particular space. In this instance, we are talking about how much "stuff" each sphere has in them. To calculate density, divide the mass of the object by its volume. So what does density have to do with the ball bearing sinking while the ping pong ball rises to the top? The swirling motion of the popping corn (which has a density somewhere between the two spheres) lets the ball bearing sink past the kernels. The same motion forces the ping pong ball upwards as individual kernels slide down, past the ping pong ball.
Part C - Pop Can Density
Objects less dense than water float, and those denser than water sink. Empty cans float, rocks sink. This is only possible because of differences in density.
If both diet and regular soda cans are placed on a double pan balance scale, it would be clear that the regular soda is heavier than the diet soda. This demonstrates the difference between mass and volume. Mass refers to how much stuff exists within an object. If something is heavier than another object, it contains more mass. Mass is measured in grams.
Volume, on the other hand, refers to how much space an object occupies. For fluids, volume is usually measured in liters (L) or milliliters (mL). There are 1000 mL in one liter. This is what we were referring to when we told you that the cans contained the same amount of liquid - 355 mL. Since both cans have the same volume, the heavier can must have a greater mass. We can now conclude that the heavier can is denser than the lighter can.
Diet sodas usually contain aspartame, an artificial sweetener, while regular sodas use sugar. Take a look at the nutritional information on the side of the cans. Notice how much sugar is in a regular soda (look under carbohydrates). Most regular sodas have about 41 grams of sugar. How much is 41 grams? Try 18 packets of sugar like the ones you might find at a restaurant! Yikes! That's a lot! Diet soda is flavored with a relatively small amount of an artificial sweetener (like aspartame) which is 200 times sweeter than an equal amount of sugar. Therefore, only a tiny amount of aspartame is needed. Both sugar and aspartame are denser than water, which can be easily demonstrated by adding small amounts of each to a container of water (they sink). So it is actually a matter of how much of each is used. The 41 grams or so of sugar added to a can of regular soda make it sink. The relatively tiny amount of aspartame used in diet sodas will have a negligible effect on the mass, enabling the can to float.
Why do cans of diet soda float? It is all due to the fact that there is a little bit of space, called "headspace," above the fluid in each can of soda. This space is filled with gas, which is much less dense than the soda itself. It is this space above the soda that lowers the density of diet drinks just enough to make them float. Sugared drinks also have this headspace, but the excessive amount of sugar added makes the can denser than water.
What's Happening?
Part A - Egg Citing
The first egg sinks to the bottom of the glass of regular tap water. This is because a raw egg has a greater density than regular tap water. Essentially, the egg has more matter stuffed into a specific area (volume) than the same amount of water. When you add salt to the water, you increase the density. That is to say, the salt packs into the same volume of water. With enough salt added to the water, the density of the water is greater than the egg, allowing the egg to float.
Part B - Ping Pong Tricks
The secret is in the densities of the ball bearing and ping pong ball. If you compare the size, or volume, of the two spheres, you'll notice that they are very similar. However, if you compare the masses of the two spheres, there is a distinct difference. The ball bearing is much heavier than the ping pong ball. The two spheres share a comparable volume, but differ in mass. That means the balls have different densities. Density is the measure of how much "stuff" is in a particular space. In this instance, we are talking about how much "stuff" each sphere has in them. To calculate density, divide the mass of the object by its volume. So what does density have to do with the ball bearing sinking while the ping pong ball rises to the top? The swirling motion of the popping corn (which has a density somewhere between the two spheres) lets the ball bearing sink past the kernels. The same motion forces the ping pong ball upwards as individual kernels slide down, past the ping pong ball.
Part C - Pop Can Density
Objects less dense than water float, and those denser than water sink. Empty cans float, rocks sink. This is only possible because of differences in density.
If both diet and regular soda cans are placed on a double pan balance scale, it would be clear that the regular soda is heavier than the diet soda. This demonstrates the difference between mass and volume. Mass refers to how much stuff exists within an object. If something is heavier than another object, it contains more mass. Mass is measured in grams.
Volume, on the other hand, refers to how much space an object occupies. For fluids, volume is usually measured in liters (L) or milliliters (mL). There are 1000 mL in one liter. This is what we were referring to when we told you that the cans contained the same amount of liquid - 355 mL. Since both cans have the same volume, the heavier can must have a greater mass. We can now conclude that the heavier can is denser than the lighter can.
Diet sodas usually contain aspartame, an artificial sweetener, while regular sodas use sugar. Take a look at the nutritional information on the side of the cans. Notice how much sugar is in a regular soda (look under carbohydrates). Most regular sodas have about 41 grams of sugar. How much is 41 grams? Try 18 packets of sugar like the ones you might find at a restaurant! Yikes! That's a lot! Diet soda is flavored with a relatively small amount of an artificial sweetener (like aspartame) which is 200 times sweeter than an equal amount of sugar. Therefore, only a tiny amount of aspartame is needed. Both sugar and aspartame are denser than water, which can be easily demonstrated by adding small amounts of each to a container of water (they sink). So it is actually a matter of how much of each is used. The 41 grams or so of sugar added to a can of regular soda make it sink. The relatively tiny amount of aspartame used in diet sodas will have a negligible effect on the mass, enabling the can to float.
Why do cans of diet soda float? It is all due to the fact that there is a little bit of space, called "headspace," above the fluid in each can of soda. This space is filled with gas, which is much less dense than the soda itself. It is this space above the soda that lowers the density of diet drinks just enough to make them float. Sugared drinks also have this headspace, but the excessive amount of sugar added makes the can denser than water.