Prescribed practical 1: speed and height

Purpose: using simple apparatus investigate experimentally how the average speed of an object moving down a runway depends on the height of the runway.

A guide to carrying out an experiment to investigate the relationship between speed and height.

Variables

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.

In this experiment the:

  • Independent Variable is the height of the runway.
  • Dependent Variable is the average speed of the marble. To calculate the average speed, we have to measure the time taken for the marble to travel a measured length of the runway.
  • Control Variables are: the distance marble travels along the runway, the mass of the marble, the type of marble used, the surface of the runway, the initial speed of the marble.

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 vertical height of the runway.

Equation

average speed = \frac{distance travelled}{time taken}

Prediction

As the height of the runway increases, the average speed of the marble will also increase.

Justification for the prediction

As the height of the runway increases the gravitational potential energy of the marble will also increase.

As the marble moves down the runway, its gravitational potential energy is converted to kinetic energy.

From the conservation of energy, the greater the amount of gravitational potential energy at the top, the greater the amount of kinetic energy at the bottom.

If the marble has greater amount of kinetic energy at the bottom of the runway, it will have greater speed.

This justifies the prediction that, average speed will increase as the vertical height of the runway increases.