This week in class we took our knowledge of density one step further as we got into the concept of density. As part of today's work I gave the students a challenge of creating a boat that held the most weight possible. The winner's boats each held 7 batteries before sinking! Quite impressive.
For homework this week, please answer the following questions. Answers are below.
You may need to check your notes or rewatch parts of the video to answer these yourself.
1. What is the definition of density?
2. If I have a bowling ball and a golf ball and the bowling ball floats while the golf ball sinks, which one has a greater density? (Be sure to think about this one for a bit before your answer.)
3. One of the examples I gave in class was of everyone in class trying to hold up a 200 lb beach ball and then trying to hold up a 200 lb mattress. How did that apply to buoyancy?
4. If something displaces as much water as it weighs, does it float or sink?
5. Think about the Bill Nye video. When the boat displaced the water in the tank, Bill Nye put the water on a balance scale with the boat. How did the weight of the water compare with the weight of the boat? Was it more, less or the same?
6. If you put a boat in a tub that weighed 5 pounds and measured the weight of the water that the boat displaced, how much would the water weigh?
7. If you crumple aluminum foil into a small ball it will sink but if you make that same amount of foil into a boat it will float. Why?
8. The winning boats (the boats that held the most batteries) all had sides. Why are sides helpful?
9. If an aircraft carrier weighs 40,000 tons, what is the weight of the water it must displace to float?
10. If something has a density greater than the density of the liquid it is floating in, will it float or sink?
11. Water has a density of 1 g/ml. If an apple has a density of .87 g/ml will it float or sink?
12. If a penny has a density of 3 g/ml will it float or sink?
Answers (Please be sure to try all the questions first. Also, if you get something wrong, know what you did wrong. Remember, these may all be on a quiz someday.)
1. Density is the amount of matter in a given space.
2. The golf ball. Strange huh. But if it sinks that means its density is greater than water, the bowling ball must have a density less that water.
3. Since the mattress was large, everyone could get under it and help hold it up. Since the ball was smaller only a few folks could help, so you couldn't hold it. Buoyancy is similar. The larger the object is, the more water can be underneath it to hold it up. Or, in other words, the more water will be displaced.
4. It floats!
5. It was the same. If you displace the amount of water you weight, you float.
6. 5 lbs.
7. If you spread out the material, more water it can displace. Once it displaces its weight in water, it will float.
8. Sides keep the water from coming into the boat. If water comes in, now you need to hold the batteries and the water. Also, sides allow the boat to displace even more water.
9. 40,000 tons! That's a lot of water.
10. Sink
11. Float
12. Sink
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