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Water density

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Transcript

  • 1. December 13, 2011
  • 2.  The density of water is very special compared to other types of liquids.
  • 3. Words to know Expand means to get bigger Contract means to get smaller Density is how close or far apart the molecules in a substance are
  • 4. Cooling things down... Often when substances are cooled down, they contract and become more dense. Often when substances are heated, they expand and become less dense. Mainly when substances are cooled, they contract and become more dense, such as metal. Pretend that if got colder and our room was to shrink a lot. We would all be forced to move closer together, making it more dense.
  • 5. Railroad Tracks When the winter weather comes around and the temperature dips, metal contracts and becomes more dense. When it is summer and the temperature rises, the metal expands and becomes less dense. That is why there are spaces between the tracks so the metal can expand in the summer.
  • 6.  Is this true for ice cubes?
  • 7.  No, it is not. We know this because when we put an ice cube into water it floats! This lets us know the ice cube is less dense than the liquid water. When water is ice it expands, therefore less dense.
  • 8.  This is key to many animals and plants surviving in the winter. When a pond freezes, it freezes on the top.
  • 9.  This allows the plants on the bottom to still have oxygen, and the animals, such as fish that live in the water, can still eat those plants. If the ice was more dense than liquid water, ice would sink to the bottom of the pond and kill everything.
  • 10. But Hold On! Please do not get confused, just because ice cubes are less dense than liquid water does not mean that cold water is less dense than hot water. Cold water is more dense, so when mixed with hot water, the hot water will float on top. There will be a video to show you this.
  • 11. Salt Water vs. Fresh Water Salt water is more dense than fresh water. That is we float better in the ocean than we do in freshwater lakes. What do you think will happen if mix coloured salt water with coloured pure water?
  • 12.  The fresh water would float on top, while the salt water would sink to the bottom. Experiment in class will be done to demonstrate this.
  • 13. Watch this video http://www.youtube.com/watch?v=Ak9CBB1bTcc
  • 14.  Which is more dense, freshwater or saltwater? Why do you think there are different lines on the Titanic for Freshwater and Saltwater? Why are there different lines for winter water and summer water?
  • 15. Hypothesis Challenge What do you think will happen if we have a glass of boiling hot water and then add an ice cube? Remember that the ice cube will melt. Think about what will happen next. There is a video on the next slide for after you finish your hypothesis.
  • 16. FUN VIDEO Watch this one if you finish early http://www.youtube.com/watch?v=GYoJiMtn_Xc&feat ure=fvsr