Experiments with Fluids: Relationship Between Weight in Air and in Water

Objects seem to weigh less when under water than when they are held outside the water. Perhaps you have noticed that when you were swimming and picked up something off the floor of the pool or lake. How can you verify that is true?

Goal

Verify that an object that does not float actually weighs less in water than in air.

Solution

Use a scale to measure the weigh of an object in an out of water.

Materials

• Full bucket of water
• Pan to catch overflow
• Spring scale
• Weight

Steps

1. Weigh the full bucket of water.
2. Weigh the weight in air.
3. Immerse the weight in the water, allowing excess to overflow into pan.
4. Weigh the weight in the water (but not setting on the bottom of the bucket nor touching the sides).
5. Remove the weight from the bucket.
6. Weigh the bucket again, without the overflow water.
7. Determine the weight of the overflow water.
8. Determine the difference between the weight of the object in and out of the water.
9. Compare the weight of the overflow water with the weight difference of the object.

Outcome

You have proven that objects weigh less in water than in air. Why is that so?

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