Modified from a PowerPoint created by www.physics4u.co.uk

This sequence of slides is designed to introduce, and explain the different kinds of variables, as explained on

pages 7 and 360 in New Physics for You, 2006 & 2011 editions.

Describe why scientists use variables. Distinguish between dependent and

independent variables.

Variables

Variables are things that

vary and change

Experiments are set-up to learn more about how the independent variable does or does not affect the dependent variable. So, for example, if you were testing a new drug to treat Alzheimer's

disease, the independent variable might be whether or not the patient received the new drug, and the dependent variable might be how well participants perform on memory tests.

What is a control group? In scientific testing, a control group is a group of individuals or cases that is

treated in the same way as the experimental group, but that is not exposed to the experimental treatment or factor.

Results from the experimental group and control group can be compared. If the control group is treated very similarly to the experimental group, it

increases our confidence that any difference in outcome is caused by the presence of the experimental treatment in the experimental group.

An independent variable

A dependent variable

Some control variables

This is the thing that you decide to change.

Determined by the question you are asking in your experiment

Example 1Investigating how a weight affects the length of an elastic band.

You decide the weight to apply, so:

Weight is the independent variable.

This is the variable that changes as a result. It is the variable that you measure.

Typically it is the problem you are trying to solve

It is the outcome of the experiment (or the thing that changes)

Example 1

Investigating how a weight affects the length of an elastic band.

You measure the resulting length of the elastic band, so:

Length is the dependent variable.

These are all the variables that must not change, to make sure it is a fair test.

Example 1

Investigating how a weight affects the length of an elastic band.

You must use the same elastic band all the time, and the same scale etc,so it is a fair test.

The independent variable is? • weight

The dependent variable is? • length of the

elasticThe control variables are? same elastic band,

same scale, etc,so it is a fair test.

Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they're supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Smithers counts how many stacks of papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks

Identify the:o Independent Variable o Dependent Variable o Control Group

What should Smithers‘s conclusion be? How could this experiment be improved?

Control Group -- Group B Independent Variable -- Special Juice Dependent Variable -- Number of stacks

What should Smithers' conclusion be? It doesn’t' work

How could this experiment be improved? Answers vary

Bart believes that mice exposed to radiowaves will become extra strong . He decides to perform this experiment by placing 10 mice near a radio for 5 hours. He compared these 10 mice to another 10 mice that had not been exposed. His test consisted of a heavy block of wood that blocked the mouse food. He found that 8 out of 10 of the radiowaved mice were able to push the block away. 7 out of 10 of the other mice were able to do the same.

Identify the:o Independent Variable o Dependent Variable o Control Group

What should Bart's conclusion be? How could Bart's experiment be improved?

Control Group - Mice not radio waved Independent Variable – radio Dependent Variable - Strength of mice

What should Bart's conclusion be? Improves strength, maybe inconclusive

How could Bart's experiment be improved? More mice, test group before and after treatment

Lisa is working on a science project. Her task is to answer the question:

"Does Rogooti (which is a commercial hair product) affect the speed of hair growth?“

Her family is willing to volunteer for the experiment.

Describe how Lisa would perform this experiment.

Identify the control group, and the independent and dependent variables in your description.

Two heads of hair, or same head with half treated and the other untreated can be used. Measure the hair growth.

Answers will vary

• In the 2nd column, put today’s date (8/15), evaluate yourself on Objectives 1, 2, 3

• At the bottom of the page, complete the thinking stem

“I used to think (something about scientific method, variables) but know I

know (something about scientific method, variables)