Variables and graphs: the bouncing ball
Drop a ball from different heights and measure its bounce. Find the independent, dependent and controlled variables, draw the graph, then change the ball and the floor in fair tests.
Core concept
In an investigation we change one independent variable, measure the dependent variable and keep the controlled variables the same; for a ball the bounce height is proportional to the drop height, so its graph is a straight line through the origin
Topic: Scientific study
Scientific research begins with a question, such as “How does the drop height change how high a ball bounces?” The variable: Something that can change in an experiment. Change one, measure another, and keep the rest the same. All key words you change on purpose is the independent variable (here the drop height). The one you measure is the dependent variable (the bounce height). Everything else must stay the same so the test is fair: these are the controlled variables (the same ball, the same floor, dropping without throwing). Measurements need units: heights here are in centimetres (cm), and 100 cm = 1 m. After measuring, we analyse the data: a table, then a graph of the dependent variable against the independent one, and finally a conclusion. A straight line through the origin means one is proportional to the other: the ratio stays the same.
What you will learn
- Identify the independent, dependent and controlled variables in an investigation.
- Plan a fair test that changes one variable at a time.
- Record data in a table with units and plot a line graph.
- Use a constant ratio and a straight-line graph to draw a conclusion.
Before you start
- Know how to read a metre rule in centimetres.
Materials
- A rubber ball, a tennis ball, a ping-pong ball, a piece of carpet
Equipment
- A metre rule fixed to a wall, a phone camera to see the top of the bounce
Procedure
- Drop the rubber ball on the concrete floor from four or more heights, and record the bounce each time.
- Keep 100 cm and try the tennis ball and the ping-pong ball.
- Keep the rubber ball at 100 cm and try the carpet.
How this simulation is simplified
- Each ball bounces back to a fixed share of its drop height: rubber 0.7, tennis 0.55, ping-pong 0.8 on concrete.
- A carpet keeps only 60% of that bounce.