Variables in Physics: A Comprehensive Guide

Teacher’s Notes - 1
This sequence of slides is designed to introduce, and explain
the different kinds of Variables
, as explained on
pages 7 and 362 in 
Physics for You
, 5
th
 edition.
Note : 
When you start this PowerPoint if you see a message about “Read-only embedded fonts”
then you are recommended to select “
Open Read-Only
” as this (i) gives a clearer font for those
at the back of the room and (ii) ensures that the text-highlighting of key words is correct.
On each slide the key points are revealed step by step, at the click
of your mouse (or the press of a key such as the space-bar).
Before making the next mouse-click you can ask questions of the
class or make statements about what is about to be revealed.
This should help students to become clearer about the ideas involved.
Naturally it pays to have quick practice-run first.
To start the slide-show, press function-key 
F5
(or right-click->Full Screen)
(to return to ‘normal view’ press the <Esc> key).
For more (free) PowerPoint presentations, visit  
www.physics
4u
.co.uk
Teacher’s Notes - 2
In order to anticipate any awkward questions from students on this
topic, it may be helpful to consider the following points, which
arose out of a discussion on the Institute of Physics NewsGroup:
--In Example 
1
 (stretching an elastic band) it shows the weight
(independent variable) changing the elastic’s length (dependent
variable).  But you could just as easily say that you were changing
the length of the elastic (independent) and then measuring how
much weight was needed (dependent).
--The simplest rule is to emphasise that the variable that 
YOU
change is the 
in
dependent (or input) variable.
--Many students would find it easier to use the terms ‘input’ variable
and ‘outcome’ variable, as these are more descriptive …but the UK
exam specifications (and exam papers) do not use these terms.
--In Example 
3
 (current in a circuit) the voltage is increased by
adding more cells.  You could say that the 
number
 of cells is the
independent variable (assumes that the cells are identical).
(This would be an example of a ‘discrete’ variable.)
Working Scientifically:
Variables
Variables
Physics for You, 5
th
 edition, 
pages 7 and 362
 
About the different types of variables,
How to identify them when doing your
practical work.
Learning Objectives
You should learn :
Variables
 
Variables are
things that
vary and change
Variables
 
In any experiment there are 3 variables:
an  
independent
 
 (or input) variable
a  
dependent
  (or outcome) variable
some  
control
  variables
 
Let’s look at each type….
Independent 
(input)
 variable
 
This is the thing that 
you
 decide to change.
Example 1
 
You
 decide the weight to apply,
so:
Weight is the 
in
dependent variable.
 
Investigating how a weight
affects the length of an elastic band.
Independent 
(input)
 variable
This is the thing that 
you
 decide to change.
 
You
 decide the initial temperature,
so:
initial temperature is the
in
dependent variable.
Example 2
 
Investigating how the rate of cooling of a beaker
depends on the initial temperature.
Independent 
(input)
 variable
This is the thing that 
you
 decide to change.
 
Which is the independent
variable as you add cells?
The voltage is the
in
dependent variable.
Example 3
 
Investigating how the current through a resistor
depends on the voltage across it.
Dependent 
(outcome)
 variable
This is the variable that changes as a result.
It is the variable that you measure.
Example 1
 
You measure the resulting length
of the elastic band, so:
Length is the dependent variable.
 
Investigating how a weight
affects the length of an elastic band.
Dependent 
(outcome)
 variable
This is the variable that changes as a result.
It is the variable that you measure.
 
You measure the temperature
every minute as it cools, so:
temperature is the dependent
variable.
Example 2
 
Investigating how the rate of cooling of a beaker
depends on the initial temperature.
Dependent 
(outcome)
 variable
This is the variable that changes as a result.
It is the variable that you measure.
 
Which is the dependent
variable here?
The current is the
dependent variable.
Example 3
 
Investigating how the current through a resistor
depends on the voltage across it.
Control variables
 
These are all the variables that must 
not
 change, to
make sure it is a fair test.
Example 1
 
 
You 
must 
use 
the 
same
 
elastic 
band 
all
the 
time
,
and 
the 
same
 
scale 
etc
,
so 
it 
is 
a 
fair 
test
.
 
Investigating how a weight
affects the length of an elastic band.
Control variables
These are all the variables that must 
not
 change, to
make sure it is a fair test.
Example 2
 
 
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
.
 
Investigating how the rate of cooling of a beaker
depends on the initial temperature.
These are all the variables that must 
not
 change, to
make sure it is a fair test.
 
Which are the control
variables here?
Use the 
same
 circuit at the 
same
temperature each time.
Example 3
 
Investigating how the current through a resistor
depends on the voltage across it.
Control variables
 
When you draw up a table of your results,
the 
in
dependent variable goes in the
first
 column, like this:
Tables
 
If you take several readings of
the dependent variable, then
you can calculate the mean (average)
 
Then your results will be more 
accurate
.
 
The 
in
dependent variable is
?
In Summary
 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
.
 
Example 1
 
The 
in
dependent variable is
?
In Summary
 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
.
 
Example 2
 
The 
in
dependent variable is
?
In Summary
 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
.
 
Example 3
 
Understand the difference between
- independent,
- dependent, and
- control variables
Be able to identify these variables
when doing your practical work.
Learning Outcomes
You should now:
For more details, see:
  
Physics for You
, 
5
th
 edition, 
pages 7, 362
For more free PowerPoints, visit
  the web-site at  
www.physics
4u
.co.uk
If you are connected to the web at the
moment, click below to see what’s
available:
     
http://www.physics4u.co.uk/
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This presentation introduces and explains different types of variables in Physics, emphasizing the concepts of independent, dependent, and control variables. It provides practical examples and tips for identifying variables in experiments, aiming to enhance students' understanding of scientific methods and principles. The content includes discussions on changing variables, defining input and outcome variables, and highlighting key points for clarity and comprehension.

  • Physics
  • Variables
  • Science Education
  • Experimentation

Uploaded on Sep 07, 2024 | 2 Views


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  1. Teachers Notes - 1 This sequence of slides is designed to introduce, and explain the different kinds of Variables, as explained on pages 7 and 362 in Physics for You, 5th edition. Note : When you start this PowerPoint if you see a message about Read-only embedded fonts then you are recommended to select Open Read-Only as this (i) gives a clearer font for those at the back of the room and (ii) ensures that the text-highlighting of key words is correct. On each slide the key points are revealed step by step, at the click of your mouse (or the press of a key such as the space-bar). Before making the next mouse-click you can ask questions of the class or make statements about what is about to be revealed. This should help students to become clearer about the ideas involved. Naturally it pays to have quick practice-run first. To start the slide-show, press function-key F5 (or right-click->Full Screen) (to return to normal view press the <Esc> key). For more (free) PowerPoint presentations, visit www.physics4u.co.uk

  2. Teachers Notes - 2 In order to anticipate any awkward questions from students on this topic, it may be helpful to consider the following points, which arose out of a discussion on the Institute of Physics NewsGroup: --In Example 1 (stretching an elastic band) it shows the weight (independent variable) changing the elastic s length (dependent variable). But you could just as easily say that you were changing the length of the elastic (independent) and then measuring how much weight was needed (dependent). --The simplest rule is to emphasise that the variable that YOU change is the independent (or input) variable. --Many students would find it easier to use the terms input variable and outcome variable, as these are more descriptive but the UK exam specifications (and exam papers) do not use these terms. --In Example 3 (current in a circuit) the voltage is increased by adding more cells. You could say that the number of cells is the independent variable (assumes that the cells are identical). (This would be an example of a discrete variable.)

  3. Working Scientifically: Variables Physics for You, 5th edition, pages 7 and 362

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

  5. Variables Variables are things that vary and change

  6. Variables In any experiment there are 3 variables: an independent (or input) variable a dependent (or outcome) variable some control variables Let s look at each type .

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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 accurate.

  17. 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.

  18. 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.

  19. In Summary 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.

  20. Learning Outcomes You should now: Understand the difference between - independent, - dependent, and - control variables Be able to identify these variables when doing your practical work.

  21. For more details, see: Physics for You, 5th edition, pages 7, 362 For more free PowerPoints, visit the web-site at www.physics4u.co.uk

  22. If you are connected to the web at the moment, click below to see what s available: http://www.physics4u.co.uk/

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