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.

7.  Is this true for ice cubes?

8.  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.

9.  This is key to many animals and plants surviving in the
winter. When a pond freezes, it freezes on the top.

10.  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.

11. 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.

12. 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?

13.  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.

14. Watch this video
 http://www.youtube.com/watch?v=Ak9CBB1bTcc

15.  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?

16. 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.

17. FUN VIDEO
 Watch this one if you finish early
 http://www.youtube.com/watch?v=GYoJiMtn_Xc&feat
ure=fvsr