Green Rocket
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Iceberg Density Experiment
Introduction
Water density can be a tricky concept to float. This experiment takes household items to make the concept a little more familiar and fun. Using ice and salt, you can visualise how water has a greater density than ice, and how the level of salinity of water can affect this to varying degrees.
Predict
Before we get started, let’s make some guesses about what might happen. Scientists like to make predictions, or hypotheses, before they do experiments. It helps them figure out what to expect and why things happen the way they do.
Have a go at making your best guess using the questions below:
- Will the ice float or sink?
- What will the ice look like in the water?
- Will adding salt to the water affect how the ice floats?
- Will the ice melt faster or slower in the different waters?
Tīmata! Let’s get started!
What You Will Need:
Water
1 Balloon
2-3 Bowls (preferably glass so you can see the whole "iceberg")
Salt
Freezer
Blue food colouring (optional)
Scissors (to cut balloon)
Step 1:
Create your iceberg. Pour water into your balloon, making sure that it will fit into your bowls. Add a few drops of blue food colouring (optional) to help visualise the iceberg floating in water. Place your balloon in the freezer for several hours or overnight so that it freezes completely.
Step 2:
Create your water conditions. Fill up your bowls with enough water for the iceberg to submerge (go underwater) entirely. The first bowl is your fresh water with no salt. The second bowl is your ocean water with 3 tbsp of salt. The third bowl if you want to test it out is your Dead Sea level water with 10-12 or more tablespoons of salt.
Step 3:
Take your iceberg out of the freezer and carefully separate the balloon from the iceberg using scissors, to cut on the stem of the balloon (adult supervision required). Carefully drop your iceberg into the first bowl with the fresh water and observe what happens. You can use a ruler to measure how much of the ice is above the water. Next place your iceberg in the bowl with 3 tbsp of salt (ocean water). How much of the ice is floating above the water? Finally, move your iceberg to the third bowl with the most salt (The Dead Sea). Record your observations.
Extra for Experts!
To dive deeper with density discussion, take an egg and talk about whether you think that it is more or less dense than different types of water. Will it float or not float in the freshwater or salt water? Test out your egg theory in both the fresh and salt water and talk about your findings.
Reflect
- What else could you change about the water to affect how the iceberg floats?
- Did the iceberg melt at a different rate (speed) in the types of water?
How Does it Work?
Water has a greater density than ice. When you add salt to the water you further increase its density. This changes the buoyancy force, or the upward force exerted by a fluid on a submerged object. Everything on Earth has a measurable density. Water density is interesting because when it freezes, its molecules expand and move further apart. This causes the frozen ice molecules to be less dense than water, even though it has changed from a liquid to a solid.
