1.21 Scientific Experiments
- Aresponding variableis a variable that the researcher predicts will change if the manipulated variable
changes. A responding variable is also called a dependent variable.
You can learn how to identify manipulated and responding variables in an experiment by watching this video about
bouncing balls:
http://www.youtube.com/watch?v=Tsqg-43Gk8c (9:21)
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/54923Q:If you were to do an experiment to find out what influences the speed of an object down a ramp, what would be
the responding variable? How could you measure it?
A:The responding variable would be the speed of the object. You could measure it indirectly with a stopwatch. You
could clock the time it takes the object to travel from the top to the bottom of the ramp. The less time it takes, the
faster the average speed down the ramp.
Q:What variables might affect the speed of an object down a ramp?
A:Variables might include factors relating to the ramp or to the object. An example of a variable relating to the ramp
is its steepness. An example of a variable relating to the object is the way it moves—it might roll or slide down the
ramp. Either of these variables could be manipulated by the researcher, so you could choose one of them for your
manipulated variable.
Experimental Controls
Assume you are sliding wooden blocks down a ramp in your experiment. You choose steepness of the ramp for your
manipulated variable. You want to measure how changes in steepness affect the time it takes a block to reach the
bottom of the ramp. You decide to test two blocks on two ramps, one steeper than the other, and see which block
reaches the bottom first. You use a shiny piece of varnished wood for one ramp and a rough board for the other
ramp. You raise the rough board higher so it has a steeper slope (see sketch below). You let go of both blocks at the
same time and observe that the block on the ramp with the gentler slope reaches the bottom sooner. You’re surprised,
because you expected the block on the steeper ramp to go faster and get to the bottom first.
Q:What explains your result?