Make Objects Float

Purpose

To demonstrate how water displacement causes objects (such as ships) to float rather than sink.

Sink or swim! Displacement specifies the position of a point in reference to an origin or to a previous position. Boats manage to stay afloat because their weight is equal or less than the water it displaces.

Required materials

• Very large jar * (note: should be an old jar as you'll need to mark it)
• Empty soda bottle
• Water
• Black permanent marker
• Notepad and pen to record results

Estimated Experiment Time

Less than an hour to set-up and conduct

Step-By-Step Procedure

• 1. Pour some water into the large jar so that it's approximately 1/2 filled
• 2. Mark a point on the jar at the top of the water-line using your black marker (note: you may also use tape to mark the point)
• 3. Pour some water into the soda bottle so it too is approximately 1/2 filled
• 4. Mark a point on the bottle at the top of the water-line using your black marker
• 5. Drop the soda bottle into the large jar (the bottle should float)
• 6. Record the results in your journal
• 7. Fill the soda bottle completely with water and again place it in the large jar
• 8. If the bottle does not completely sink, mark the new water-line on the jar
• 9. Record the results in your journal

Note

Depending on the size of your jar (and your soda bottle) the bottle may not sink when it's completely full. If that's the case, try using a slightly smaller jar or larger soda bottle.

Observation

Make sure to make careful observations of what's happening each time you drop in the bottle. Marking the bottle and jar allows you to track the differential of water displacement. Be sure to record the variance in your journal so you can answer questions about the experiment. For example: What happened when you dropped in the bottle of soda when it was 1/2 full? How much water was pushed up in the jar? Did the bottle sink? What happened the second time when the bottle was filled with water? Can you describe the process of displacement in relation to this experiment?

Result

When the bottle with 1/2 water was dropped into the jar, the weight of the bottle caused the water to rise by pushing it away from itself. The difference between the marked water-line on the jar and the new one is how much water was pushed away or displaced. The second time when you filled the soda bottle with water and dropped it into the jar, it sank to the bottom because it became heavier than the water it was pushing away.

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