Help! I’m Drowning                                                                  Name ____________________________________

 

Background Information

            Would you rather drown n salt water or fresh water?  Of course this is a really silly question.  Drowning is frowning, no matter what type of water you drown in.  But suppose the question was stated differently: “Imagine that you are in danger of drowning.  Would you rather be in fresh water or salt water?”  Keep this questioning mind as you carry out this activity.

 

Materials


pen with waterproof ink

ruler

scissors

beaker (about 1 L)

stirring rod

modeling clay

plastic drinking straw

table salt

balance


 

 

 


Procedure

  1. Make a metric scale on the straw with the permanent marker by placing marks 1 cm apart from the non flex end.  Number your marks. Now place a mark half way between the lines to mark the half cm
  2. Make a round ball of clay about 1.5 cm in diameter.  Push the claw into the end of the straw  at the zero end of the scale.
  3. Fill the beaker almost full with water. Place the straw in the water vertically with the clay end down, as shown. The straw should float. If it does not, make the claw ball larger or smaller. If it leans to one side make the ball round.
  4. Note where the surface of the water touches the metric scale.  Record the number in your data table.
  5. Remove the straw from the water.  Use the balance scale to measure 10 g of table salt in the small plastic cup.
  6. Stir the salt into the water.  Place the straw back in the water.
  7. Note where the surface of the water touches the metric scale.  Record the number in your data table.
  8. Remove the straw from the water.  Measure out 10 g more of table salt and stir it into the water. Now you have a total of 20 g of salt in the water.
  9. Place the straw back in the water. Where does the surface of the water touch the metric scale?  Record the number in your data table.
  10. Repeat steps 9 and 10 two more times.  Record the numbers in your data table.
  11. Now add 4 ice cubes to the salt water. Place the straw back in the water. Where does the surface of the water touch the metric scale?  Record the number in your data table.

 

Data Table

 

No salt

10 g Salt

20 g salt

30 g Salt

40 g Salt

Ice Water

Height of straw in water

 

 

 

 

 

 

 


Critical Thinking and Application

1. How did the position of the straw change as you added more salt to the water?

2. What does this tell you about the way objects float in salt water compared with the way objects float in the fresh water?

3. Suppose you were in danger of drowning.  What would be an advantage of being in salt water?

4. What other factors might come into play as you consider whether you would rather be in fresh water or in salt water if you were in danger of drowning?

5. How did the position of the straw change when you added the ice cubes.

6. Explain why the temperature makes a difference