Page 8 - 新思维科学学生用书5 样章

Working like a scientist

Fair testing

In a fair test we change one factor or variable and keep all the others the same in order to

try to answer a scientific question. By changing only one variable, we know that no other

variable will affect the results of the test. A fair test involves three types of variables:
• The variable we change is called the independent variable.

• The variable we measure or observe that changes is called

the dependent variable.
• The variables we keep the same are called the

control variables.
For example, in Unit 2 when we investigate which material muffles sound best, the

control variable is the source of sound because we keep this the same. The independent

variable is the muffling material because we change this from newspaper to bubble wrap
to a blanket. The dependent variable is the sound volume we measure, because this

changes according to which muffling material we use.

Observing over time

In investigations we often need to observe changes caused by things we do. For example,
what happens to water when we freeze it, or what happens when we mix sugar and

water? How often we need to observe depends on the changes we are looking at. We can

see some changes straight away, such as the change in colour of iodine solution when
starch is present. If we observe what happens when we mix sugar and water, we can see

the change in a few minutes. The changes to water when it freezes will take a few hours to

observe. Observing changes in nature can often take longer. When we investigate what
happens when a seed germinates, we will need to observe changes over days or weeks,

depending on the type of seed. We will need a whole year to observe the changes that
happen as the seasons change.

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