Question

A student wants to know if the effect of gravity is the same on all objects. She follows these steps:

1. Drop a 5-gram ball, a 10-gram ball, and a 12-gram ball from a height of 10 meters.
2. Record how long it takes for each object to hit the ground.
3. ???
Which step should be next?
A. Measure the mass of the balls again.
B. Choose new balls.
C. Drop the balls from a different height.
D. Perform a second trial.

Answer 1

D. Perform a second trial.

Repeating the drops (replication) checks for random errors and improves reliability — you can average the times and see whether results are consistent. Measuring mass again is unnecessary unless you suspect an error; changing balls or heights would introduce new variables and should be a separate test.