## 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?

1. By using objects of the same mass, the students can learn about both the effect of the mass and the effect of the shape.
2. By using objects of the same mass, the students can learn about the effect of the mass.
3. If they do not use objects of the same mass, the students cannot learn about the effect of the shape.
4. It is NOT important for all the objects to have the same mass because the students are not testing the effect of the mass.

Distribution of Responses

Percent of students responding correctly

 Overall 53% Grades 6–8 45% Grades 9–12 62% Male 51% Female 54% Primary Language is English 55% Primary Language is not English 37%