1. How Science works:
Types of
Variables

2. About different types of variables,
Learning Objectives
You should learn :
About different types of variables,
How to identify them when doing your practical work.

3. Can you remember what is meant by… …an independent variable?
Revision of variables
Can you remember what is meant by…
…an independent variable?
…a dependent variable?
…a control variable?

4. Revision of variables Summary:
The independent variable is the one that you change or select.
The dependent variable is the one changes as a result, and that you measure.
The control variables must not change, so that it is a fair test.

5. Categoric Ordered Discrete Continuous Types of variables
There are 4 other types of variables that you may meet.
Their names are:
Categoric
Ordered
Discrete
Continuous
We’ll look at two examples of each one.

6. Categoric variables These have word labels. Example 1
In this experiment on conduction of heat:
The Categoric variables are:
copper, iron, glass

7. Categoric variables These have word labels. Example 2
In this experiment to find the resistance of wires:
The Categoric variables could be:
copper wire, iron wire, steel wire, etc

8. Ordered variables
These are categoric variables that can be ranked, in an order.
Example 1
In this experiment to find the resistance of wires:
The Ordered variables could be:
thick copper wire, thinner copper wire, very thin copper wire.

9. Ordered variables
These are categoric variables that can be ranked, in an order.
Example 2
In an experiment to investigate a falling parachute:
The Ordered variables could be:
large parachute, medium parachute, small parachute.

10. Discrete variables
These variables can only have whole number values, 1, 2, 3,…
Example 1
In an experiment to investigate the stretching of a spring:
The discrete variables are:
1 weight, 2 weights, 3 weights, …

11. Discrete variables
These variables can only have whole number values, 1, 2, 3,…
Example 2
In an experiment on the cooling of an insulated beaker:
The discrete variables are:
number of layers of insulation = 1 layer, 2 layers, 3 layers, …

12. Continuous variables These variables can have any numerical value.
Example 1
In this experiment to investigate the stretching of a spring:
The continuous variable is:
length of the spring = 15.1 cm, cm, cm …

13. Continuous variables These variables can have any numerical value.
Example 2
In this experiment to investigate the cooling of water:
The continuous variable is:
the temperature of the water = 70.6oC, 68.4oC, 66.2oC …

14. In summary Categoric These have word labels. Ordered
These categoric variables can be ranked, in an order.
Discrete
These can only have whole number values.
Continuous
These can have any numerical value.

15. Independent (input) variable
This is the thing that you decide to change.
Example 1
Investigating how a weight affects the length of an elastic band.
You decide the weight to apply, so:
Weight is the independent variable.

16. Independent (input) variable
This is the thing that you decide to change.
Example 2
Investigating how the rate of cooling of a beaker depends on the initial temperature.
You decide the initial temperature, so:
initial temperature is the independent variable.

17. Independent (input) variable
This is the thing that you decide to change.
Example 3
Investigating how the current through a resistor depends on the voltage across it.
Which is the independent variable as you add cells?
The voltage is the independent variable.

18. Dependent (outcome) variable
This is the variable that changes as a result. It is the variable that you measure.
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.

19. Dependent (outcome) variable
This is the variable that changes as a result. It is the variable that you measure.
Example 2
Investigating how the rate of cooling of a beaker depends on the initial temperature.
You measure the temperature every minute as it cools, so:
temperature is the dependent variable.

20. Dependent (outcome) variable
This is the variable that changes as a result. It is the variable that you measure.
Example 3
Investigating how the current through a resistor depends on the voltage across it.
Which is the dependent variable here?
The current is the dependent variable.

21. Control variables
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.

22. Control variables
These are all the variables that must not change, to make sure it is a fair test.
Example 2
Investigating how the rate of cooling of a beaker depends on the initial temperature.
You must use the same beaker, with the same amount of water, in the same position in the room, at the same room temperature, so it is a fair test.

23. Use the same circuit at the same temperature each time.
Control variables
These are all the variables that must not change, to make sure it is a fair test.
Example 3
Investigating how the current through a resistor depends on the voltage across it.
Which are the control variables here?
Use the same circuit at the same temperature each time.

24. Tables When you draw up a table of your results,
the independent variable goes in the first column, like this:
If you take several readings of the dependent variable, then you can calculate the mean (average)
Then your results will be more reliable.

25. same elastic band, same scale, etc, so it is a fair test.
In Summary
Example 1
The independent variable is ?
weight
The dependent variable is ?
length of the elastic
The control variables are ?
same elastic band, same scale, etc, so it is a fair test.

26. temperature as it cools
In Summary
Example 2
The independent variable is ?
initial temperature
The dependent variable is ?
temperature as it cools
The control variables are ?
the same beaker, with the same amount of water, in the same position in the room, at the same room temperature, so it is a fair test.

27. In Summary voltage (p.d.) current
Example 3
The independent variable is ?
voltage (p.d.)
The dependent variable is ?
current
The control variables are ?
the same circuit, at the same temperature each time, so it is a fair test.