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To investigate experimentally the extension of a spring and how it is related to the applied force, and recall that the extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

The main variables in a science experiment are the independent variable, the dependent variable and the control variables.

The Independent Variable is what we change or control in the experiment.

The Dependent Variable is what we are testing and will be measured in the experiment.

The Control Variables are what we keep the same during the experiment to make sure it’s a fair test.

Variables

In this experiment the:

• Independent Variable is the stretching force F. This is the weight attached to the spring and is calculated using W = mg.
• Dependent Variable is the extension of the spring e.
• Control Variables are the material of the spring, and the cross section area of the spring. These are kept the same by not changing the spring during the experiment. Remember - these variables are controlled (or kept the same) because to make it a fair test, only 1 variable can be changed, which in this case is the stretching force (i.e. the weight attached to the spring).

Prediction

As the stretching force (i.e. the weight attached to the spring) increases, the extension of the spring will also increase.

Justification for the prediction

The greater the stretching force the greater the separation of the atoms of the spring. This will result in the spring having greater length and so greater extension.

Safety

Safety goggles must be worn throughout the experiment.

The spring is stretched and could fly off and hit someone in the eye.

The retort stand must be secured to the bench with a clamp to prevent it from falling over and hurting someone or falling on their feet.

Put a barrier in place to prevent feet being underneath the spring.

This is to ensure that if weights fall off the spring they do not fall onto someone’s feet.