Item CV012003: To find out if the shape of objects has an effect on how fast the objects sink, it is important that all the objects tested have the same mass because if they didn't have the same mass, it wouldn't be possible to learn about the effect of shape on how fast they sink.
A science class wants to find out if the shape and the mass of objects made of the same metal affect how fast these objects sink in water. One group tests the effect of the shape, and another group tests the effect of the mass. The students who test the effect of the shape use three objects that have the same mass but different shapes. The students drop each object into a large water tank and measure how long it takes for each object to reach the bottom of the tank.
Why is it important that the students use objects of the same mass?

Distribution of Responses Percent of students responding correctly
 