Writing hypotheses

In the practical exam you may be required to create a hypothesis and to obtain results from a given experiment method.

Scientists use hypotheses to explain things that they observe. Hypotheses can be tested to confirm whether or not a variable has an effect on another variable, and what the relationship is between the variables.

A hypothesis in practical work is a prediction that is supported with an explanation. The explanation might use previous knowledge or scientific evidence.

You may have to suggest a testable hypothesis for your practical assessment. These are three examples of predictions for stretching a spring. A is a simple prediction, B is slightly more detailed, and C is a very detailed prediction.


A. There is a link between the length of a spring and the amount of weight put on it.

B. I think that if I add more weight to the spring it will get longer and its extension and weight might be proportional to each other.

C. I think if I double the weight on the spring, the extension will also double. The extension of the spring and the weight might be directly proportional to each other.


I think this because I’ve used newton meters that have springs inside, and they get longer when I add weights. The newton meters have scales written on the side for measuring force and the scale lines are equally spaced for multiples of the same amount of weight added.

This prediction can be tested in the lab.


All practical predictions imply some sort of relationship between an independent variable, and a dependent variable. To make sure that the effect of changing only one variable on the dependent variable is investigated, other variables are kept the same. They are the control variables.


What is the independent variable in the above predictions of an investigation?

The weight added to the spring.


What is the dependent variable in the investigation?

The length or extension of the spring.


What are the control variables in the investigation?

The spring used must be the same throughout. The length of the spring (or extension) should be read from the same place for each measurement.