Hot – Cold Water

DESCRIPTION:
Hot water expands so it is less dense than room temperature water. Cold water contracts so it is more dense than room temperature water. The red hot water rises and the blue cold water sinks.

TOPICS COVERED:
density
physical change
thermal convection

MATERIALS NEEDED:
– large beaker (~4L)
– a small glass bottle with red hot water
– a small glass bottle with blue cold water
– something to set the bottles on; a stack of microwells works well
– nitrile gloves

PROCEDURE:
1. Fill the small bottles accordingly and set them to cool and heat
2. Place the stack of microwells in the bottom of the beaker
3. Fill the beaker ~3/4 full of room temperature water
4. Using gloves, hold a bottle in each hand so that your thumb is covering the top hole and your other fingers are holding the bottom of the bottle
5. Slowly lower the bottles into the beaker so that your thumbs are closest to you
6. Set the bottles carefully on the microwells and let go of the bottles

ADDITIONAL COMMENTS:
You want the beaker to be as full as it can be, but not so full that putting both of your hands in causes the beaker to overflow. Make sure the beaker is set up wherever you want the demo to be displayed, because moving the beaker insures that the water and colors will mix. The hot water does not need to be boiling, you should still be able to easily handle the bottle.

SAFETY:
Safety goggles should be worn at all times. Caution should be taken with the hot bottle.

REFERENCES:
Meerman, Ruben. “Hot and Cold Water.” Posted 21 Dec 2006. Accessed 17 June 2010. http://www.abc.net.au/science/surfingscientist/pdf/teachdemo10.pdf

STORY:
This can be correlated to how lakes are warm on the surface and cold on the bottom.

Handout