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Plenty of educational tools available at gateway Learning Corporation

Sinking & Floating

Science project supplies

Getting Started

Did you know an object s density helps determine whether it floats or sinks in water? And does the density of the water also affect whether an object floats or sinks? Do you know if objects float better in saltwater than they do in fresh water? *In this activity you will determine if salinity, the amount of salt in a liquid, affects whether an object floats or sinks.

You will need:

1 marking pen
1 small raw potato
1 500-ml beaker
1 stirring spoon
1 tablespoon
1 metric ruler H cup (119 ml) salt
tap water
1 leveling knife
safety goggles

*Note: It's important that you complete this activity before you build your submarine. The scientific principles you learn in project will help you design your sub later.


1.Use the marking pen to draw a horizontal line on the beaker 4 cm from the top.

2.Fill the beaker to the marked line with tap water.

3.Place the potato in the beaker. Observe the potato's position in the water. Record your observations in the chart.

4.Use the stirring spoon to remove the potato.

5.Stir one level tablespoon of salt (15 ml) into the beaker of water until it dissolves.


Amount of Salt Position of Potato in the Water
1 T  
2 T    
3 T  
4 T  
5 T  
6 T  
7 T  

6.Gently place the potato in the beaker. Observe the potato's position. Record your observations in the chart.

7.Repeat steps 4, 5, and 6 until the potato stops moving.


1.If you used a larger potato in this experiment, would the results be the same? Explain your answer.

2.Explain why things are more buoyant in saltwater than they are in fresh water.

3.Based on your findings, would a submarine need more weights (ballast) in fresh water or saltwater?

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