1. Fair & Accurate Experiments
D. Crowley, 2007

2. Fair & Accurate Experiments
Saturday, November 17, 2018
Fair & Accurate Experiments
To be able to plan fair and accurate experiments

3. Thermometer How do you think a thermometer works?
The liquid (e.g. mercury) expands when it gets hotter making it move up the glass tube
The hotter it gets the more it expands, and therefore the further it moves up the thermometer…

4. Experiment
Today you are going to conduct an experiment to see which will boil first, a beaker containing lots of water, or containing much less…
Small quantity of water
Larger quantity of water
You will also need to explain your findings using your scientific knowledge of particles…

5. Variable
Before we start our experiment we need to identify a few key procedures
What does a variable mean?
During an experiment lots of things can be changed - these changes are called variables
In a scientific experiment you should only ever change one variable (your experimental variable). All the other factors should remain the same (controlled variables) - this makes the experiment fair!
E.g. say you were making chocolate cakes, but they weren’t tasting quite right. Would it be wise to change all your quantities of sugar, flour, eggs and chocolate at once? How would you know which change would make the cake taste great?

6. Variables
It is very important for the reliability of an experiment that only one variable is changed - from now on any experiment you do will require controlled variables and one experimental variable
E.g. if you want to find out the best recipe for chocolate cakes, you wouldn’t change all the ingredients at once. Instead, you may keep the amount of sugar, flour and eggs the same (controlled variables), but change the amount of chocolate you put in (experimental variable)
If the cake tastes great, then good job. If not, we would start again, this time maybe keeping our chocolate, sugar and eggs quantities the same, but maybe change the flour…

7. Planning
Which will boil first - a beaker with a small or large amount of water?
How can we carry out this experiment?
Apparatus (you do not have to use all of these): stop clock; Bunsen burner; string; measuring cylinder; heat-proof mat; thermometer; tripod; gauze; different sized beakers
Now you need to plan for your experiment - on your sheet write down the key variables and how it will affect the experiment
E.g. amount of water - more water will take more/less time to heat up (I will use 25cm3, then 50cm3, then 75cm3, then 100cm3 etc…)!
E.g. distance from heat - the closer the beaker is to the heat the quicker/slower it will warm
E.g. heat setting on Bunsen - if the Bunsen is on a medium heat this will heat the water quicker/slower
E.g. beaker used - a small thin beaker will warm quicker/slower than a large thick beaker

8. Control What variable are you changing (experimental variable)?
What variables will you need to control (controlled variables) to make this experiment fair?
Explain how you will control the controlled variables
For example
I am going to change the quantity of water - e.g. 100cm3, 200cm3, 300cm3, 400cm3…
I will use the same size beaker;
I will keep the beaker a set distance from the Bunsen;
I will keep the Bunsen on a constant heat;
I will be as accurate as possible with the stop watch (perhaps the same person can operate this)

9. Risk Assessment
Finally, before we start we must carry out a risk assessment
This is very important as we can think ahead, and hopefully plan for some of the dangers we might face in this experiment…
What will we be using in this experiment?
What dangers are there?
What action should we take?

10. Carry out your experiment
Record your results as you go (in the table) – once you have worked out an average for the time taken for a quantity of water to boil, write your average onto the class computer
Amount of water (cm3)
Time taken to boil (sec)
Average (sec)
Test 1
Test 2
Test 3
100
200
300
400
500
Calculate an average: cross out anomalies (we will not use these in the average, e.g. 84, 86, 102, 72)
Add up the numbers you have left (e.g = 243)
Divide your answer by the amount of numbers you have (e.g. 242 ÷ 3 = 81)