A student drops a piece of paper and records the time for the paper to hit the floor. The student then folds the paper in half and repeats the process. The student does this four more times, each time, folding the paper in half. The student
always drops the paper from the same height.
The independent variable is the:

A. Dimensions of the paper

B. The time to hit the floor

C. The height of the drop

D. The temperature of the room

The answer is: A - Dimensions of the paper.

Explanation:

"A" is the independent variable because it is the only thing that you are manipulating in each trial (i.e. folding the paper in half each time). "B" is the dependent variable because it is what you are measuring in every trial. "C" and "D" remain constant (they aren't changed at all) so they are neither dependent or independent variables.

pure substance: iron,copper

impure substance: water,charcoal