Question

Object To Be Dropped Drop Height (meters)
10-gram ball 5
5-gram ball 8
18-gram ball 10
A student designs an investigation to study the effect of gravity on objects on Earth. He will use the criteria shown. How can the student improve the investigation?
A. by finding balls made from different materials
B. by dropping the balls from the same height
C. by measuring the circumference of the balls
D. by using balls that are the same mass

Answer 1

B. Drop the balls from the same height.

Reason: using different drop heights introduces a confounding variable. To test how gravity affects objects you should keep the starting height the same (and control shape/material/size or air resistance) so any differences in fall time are due to the objects, not differing drop heights.