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AP® Physics 1 & 2

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Difficult

Density Experiment

APPH12-OXE5VJ

A student is designing an experiment to determine how (or whether) the density of water changes as it is cooled, but without freezing the water. The student decides to float a wooden cube in a container of water at room temperature and mark the water level on the cube with a line. The container with the water and cube will then be placed in the refrigerator. Every 5 minutes, the student will remove the container to measure the temperature of the water and mark the water level on the cube with color coded lines. The student reasons that if the water's density changes, the cube will float higher or lower in the water as a result.

There are some problems with this procedure that might interfere with the student’s ability to draw reliable conclusions from the experiments. Which of the following is NOT likely to affect the reliability of the results?

A

The wood might absorb water, changing the density of the wood. This would cause the wood to float lower or higher independent of changes to the water's density.

B

The refrigerator will cool the wood as well, which might change the density of the wood. This would cause the wood to float lower or higher independent of changes to the water's density.

C

The air in the refrigerator is cooler than room temperature, which will change the magnitude of the buoyant force on the cube from the air. This will cause the wood to float higher in the refrigerator, but lower when it is taken out to be measured.

D

The color-coded lines could be so close together that they seem to overlap, even if the water level on the cube did change. This will make it look like nothing is changing even if there really are very small changes taking place.