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Essential Science for Teachers: Physical Science

Rising and Sinking Children’s Ideas About Rising and Sinking

Children’s Ideas About Rising and Sinking

Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science. Consider what evidence might refute this idea, and why a child would be likely to believe this? Once you’ve entered all your answers you can click “printable page” at the bottom of this form to print your answers. You can also click “see possible response” for any question to see one possible response from the series content advisors.

1. A larger piece of candle will sink or float lower in the water than a smaller piece.

When presented with a comparison between two objects made of the same material but of different sizes, children often think that while the smaller object will float, the larger object will either float lower in the liquid or sink entirely. However, if a smaller piece of a given material floats in a liquid because it is less dense than the liquid, the same will be true for a larger piece of the same material.

2. The depth of the liquid has an effect on the level at which something floats.

The amount of fluid that an object floats in has no effect on the level at which it floats. The level at which it floats is a function of how much of the fluid it displaces, which in turn determines the buoyant force.

3. When only a small portion of an object is above the surface of a liquid, it is partially floating and partially sinking.

An object that is partially above and partially below the surface of a liquid is floating. Again, objects float at different levels due to how much water they displace.

4. Water “holds up” an object that floats in it.

Elementary school children don’t often have much experience with the concept of balance of forces. If the weight of a submerged object is greater than the buoyant force, the object will sink. If the buoyant force is greater than the weight of the completely submerged object, it will rise to the surface and float.

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Essential Science for Teachers: Physical Science


Produced by Harvard-Smithsonian Center for Astrophysics. 2004.
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  • ISBN: 1-57680-749-5