http://www.ck12.org Chapter 1. Introduction to Physical Science
A:The block on the steeper ramp would have reached the bottom sooner if all else was equal. The problem is that
all else was not equal. The ramps varied not only in steepness but also in smoothness. The block on the smoother
ramp went faster than the block on the rougher ramp, even though the rougher ramp was steeper.
This example illustrates another important aspect of experiments: experimental controls. Acontrolis a variable that
must be held constant so it won’t influence the outcome of an experiment. In the case of your ramp experiment,
smoothness of the ramps should have been controlled by making each ramp out of the same material. For other
examples of controls in an experiment, watch the video at the URL below. It is Part II of the above video on
bouncing balls.
http://www.youtube.com/watch?v=LeqOQQRzCfo (5:44)
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/54924Q:What other variables do you think might influence the outcome of your ramp experiment? How could these other
variables be controlled?
A:Other variables might include variables relating to the block. For example, a smoother block would be expected
to go down a ramp faster than a rougher block. You could control variables relating to the block by using two
identical blocks.
Summary
- An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on
different values. - There must be at least two variables in any experiment: a manipulated variable and a responding variable.
- A control is a variable that must be held constant so it won’t influence the outcome of an experiment.
Vocabulary
- control: Variable in an experiment that is held constant so it will not influence the outcome.
- experiment: Controlled scientific study of a limited number of variables.
- manipulated variable: Factor that is changed, or manipulated, by a researcher in a scientific experiment; also
called independent variable. - responding variable: Factor in an experiment that is expected to change, or respond, when the manipulated
variable changes; also called dependent variable.
Explore More
Do virtual experiments with objects sliding down ramps at the following URL, and then answer the questions below.
For the y-axis, selectY pos(position of the object relative to the starting point), and for the x-axis, selecttime
(time elapsed since the object started moving). From the controls, select one variable other thandelta Tto be your
manipulated variable. Change this variable while controlling the others, and observe how it affects the movement of
the object down the ramp.