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Outcomes
Outcomes
Explain the differences between independent and dependent variable.
Explain how to control the variables (keep them the same).
Explain what a control is in an experiment.
Carrying out a fair test
Carrying out a fair test
Factors that affect the results of an experiment are called VARIABLES.
A FAIR TEST is when only one variable is changed during an experiment and all the other variables are kept the same.
To design a fair test you should know:
the problem you are trying to solve (aim)
exactly what you are going to measure (dependent variable)
what you are going to change (independent variable)
what you are going to keep the the same (controlled variables)
anything else that might affect the experiment but you cannot control
What is a fair test?
What is a fair test?
Cows Moo Softly
Cows = Change: The independent variable; what are we going to change
Moo = Measure: The dependent variable; what are we going to measure
Softly = Same: The controlled variables; for our test to be fair, we need to control all the other variables.
Our experiment is reliable if we repeat it and get the same results.
Variables in Scientific Investigation
Variables in Scientific Investigation
Identify the independent, dependent and controlled variables for each scenario. (Write them into your exercise book)
A group of students decide to investigate the time taken for a candle to go out in closed containers of different volumes.
A group of students decide to investigate the effect of time on the degree of rusting of a nail immersed in tap water.
A group of students decide to compare the heat insulating properties of a synthetic material and a natural material using containers of hot water and a thermometer.
A group of students decide to find out if there is any difference in the change in mass over a period of 5 days between seedlings left in the dark and similar seedlings exposed to light for the same period.
A group of students decide to compare the effect on rusting of iron nails of painting, oiling and galvanising the nails. They decide to measure the degree of rusting by finding the change in mass of each nail after 2 weeks.
A group of students decide to use a spring balance to investigate the relationship between mass (in kilograms) and weight (in newtons).
A group of students decide to compare the effect on iron nails of salt water, acidified water and tap water. They decide to measure the degree of rusting visually.
Another group of students decide to compare the effect on iron nails of salt water, acidified water and tap water. They decide to measure the degree of rusting indirectly, by measuring the reduction in oxygen levels in sealed containers containing a nail, air, cotton wool, an oxygen sensor and the particular type of water.
A group of students decide to compare the effect of the thickness of a length of wire on the electric current in a circuit.
A group of students decide to investigate what happens if the number of batteries (or bulbs) in a series circuit is altered.
A group of students decide to investigate the differences in the pH of a range of soft drinks.
A group of students decide to investigate the optimum temperature for seeds to germinate.
A group of students decide to investigate how, in a sealed jar containing iron and a little water, the oxygen level in the air is affected by the mass of the iron.
A group of students decide to investigate the effect of temperature on the transpiration rate of a plant.
A group of students decide to investigate the loss of heat through bright and dull surfaces.
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