Density of an object is what determines whether it will float, like ice in your drink, or sink, like dropping a rock in a pond. Density is based on the mass and volume of an object. Floating and sinking doesn’t just happen with solid objects: It can happen with other substances. Liquids and gasses can sink and float too.
Created by Suncheli Project from Noun Project
Student Guide
Turning Thermal Tides
Experimenting with water and heat
How will hot and cold water move when they are placed together?
This resource was originally published in PhysicsQuest 2019: Heat.
How will hot and cold water move when they are placed together?
- Rough grain sandpaper
- Fine grain sandpaper
- 4 nuts
- Fun dough
- Rubber bands
- Ruler
- Tape
Intro
Before the experiment
Think of a drink that recommended you shake it before you drink it.
- Why did you have to shake it?
- What did that have to do with the densities of the different ingredients in the drink?
Have you ever noticed that the air is warmer in a room the higher up you move?
- Have you noticed it is colder near the floor?
- What does that tell you about the densities of the warm and cold air?
How do you predict the hot and cold water will move when they are placed together?
Setting up
Fill the first 20 oz. bottle two-thirds of the way full with very hot water. Use caution: This needs to be done carefully to avoid getting burned! Fill the second 20 oz. bottle two-thirds of the way full with very cold water.
Place one dye tablet in each bottle. Make sure the dye tablets are different colors.
Place one end of the clear plastic tube into one of the bottles. The middle of the tube should be at the top of the bottle.
Use the clay to secure the tube and seal the gap between the opening of the bottle and the sides of the tube.
This next step will be slightly difficult so you may want to do it over a baking sheet, sink, or bucket. Tip the bottles, and very carefully slide the other end of the tube into the second bottle. Try not to let the water in the two bottles mix.
Seal the second bottle securely with clay. You should now have two bottles, attached with a plastic tube and clay, laying on their sides. Hot water of one color should be in one bottle and cold water of another color should be in the other.
During the experiment
Collecting data
- Hot on Top
Hot on Top:
Carefully turn the bottles so that the bottle with the hot water is on top of the bottle with cold water. If you’ve sealed it well, there should be very little spillage. Now watch for a full 2 minutes and record everything that is happening:
- What do you notice?
- How is the water on the bottom behaving?
- Can you tell if it's moving? How?
- Cold on Top
Cold on Top:
Set up the experiment again exactly as described in the “Setting Up the Experiment” section. This time, turn the bottles so that the cold water is on top of the bottle with the hot water. Watch again for two minutes.
- What do you notice?
- How is the water on the bottom behaving?
- Can you tell if it's moving? How?
Analyzing data
What were your results?
- What did you observe when you put the hot water bottle on top of the cold water?
- What difference did you observe when you reversed the order of the bottles to put the cold water on top?
- In which order did you see the water mixing together the fastest? Why do you think this happened?
Conclusion
What claim can you make in regards to the density of hot and cold water?