Description of activity
Build an air-fuelled car in which wheel size is compared to determine efficiency and effectiveness.
This activity could take up to two hours:
- build the vehicle and gather data
- display and analyse data.
Students estimate and measure distances, carry out a first-hand investigation to gather, record and display data in such a way as to be able to make predictions.
Knowledge and understanding
- Cardboard, balloons, sticky tape, reusable putty
- Plastic bottle tops or similar, of different sizes (at least four of each size) to act as wheels
- Straws (straight and bendy), wooden skewers
- Tape measure or metre ruler
- Stopwatch or timer
- A description of the experimental method used
- Data recorded in tables and graphs
- A written analysis/explanation of this data
Work, health and safety
Check relevant Work, health and safety guidelines.Evidence of work for assessment purposes
STEM teaching and learning activities
This activity can be carried out effectively in groups of three students. Each student can be allocated a role:
- Experimenter– carries out the experiment
- Measurer – measures the distance and times
- Recorder – records the results and shares them with the group.
Each student carries out one trial and then swaps duty, so that each measurement has three values which should then be averaged. See student involvement in practical activities.
- Students follow instructions to build a balloon-powered car (a vehicle powered by air escaping from a balloon).
- The aim of this investigation is to determine whether the size of the wheels affects the speed of the car. In order to ensure that the size of the wheels is the only thing that is changed in this experimental setup, students must determine how to make sure that there is an equal force on the car for every trial.
- Speed is a measure of the time it takes for an object to travel a given distance. Students can set up their experiment by measuring a given distance, eg 1m and timing how long it takes for the car to travel that distance.
- Students record their results in a table.
- Students calculate the speed of the car by substituting the average speeds in the following formula:
- The appropriate units for speed are ‘metres/second’, recorded as ‘m/s’, for example if it takes a car 10 seconds to travel 1 metre then the speed is 1/10 m/s or 0.1 m/s. These results can then be recorded in a different table.
- This data can then be transferred into a column graph so that the relationship (if any) between wheel size and speed can be seen
- Students analyse this data to draw a conclusion
Circumference– the distance around the circle
Data – facts or figures that can be used to draw conclusions
Fair test – an investigation where one variable (the independent variable) is changed and all other conditions (controlled variables) are kept the same; what is measured or observed is referred to as the 'dependent variable'
First-hand investigation – an inquiry based in the direct use of observation or measurement
Force – a push, a pull or a twist
Friction – a contact force that will affect the motion of an object
Graph – a diagram showing the relation between variable quantities
Table – a set of facts or figures systematically displayed in columns and rows
Key inquiry questions
How can you make this a fair test?
In order to compare the results of one trial with another, the only factor that should be changed is the one being tested – in this case the size of the wheels. The amount of air in the balloon will affect the force on the car and thus its speed. Students thus need to determine how they are going to control the amount of air in the balloon. The surface on which the car travels also must remain the same as the amount of friction will affect the speed of the car.
How much data do you need?
In any collection of experimental data it is important to take a number of readings/do a number of trials, and then take the average of these readings. This reduces the effect of a ‘fluke’ result and thus increases the reliability of the data. Sometimes this can be achieved by having every group follow exactly the same method and then combining results. By allocating roles to group members and swapping the roles so that each group member does each task at least once, a number of trials are performed and results can be combined.
How can you use tables effectively?
Tables are structured in a way that makes it easy for other people, reading the table, to understand what was done to generate the data in the table. Each column should have a title which contains a description of the data AND the units of measurement in brackets, eg 'Time taken (s)'. The first column (on your left-hand side) should contain the values of the condition that has been changed (the independent variable). In this way, someone looking at the table can tell what was done in the investigation. The first column tells you what was changed, the other columns tell you what was measured and these two factors are the essence of the investigation.
How can you use graphs effectively?
Graphs are also structured in a way that makes it easy for other people, reading the graph, to understand what was done to generate the data shown in the graph. Each axis should have a title which contains a description of the data AND the units of measurement in brackets, eg ‘Time taken (s)’. The X axis (horizontal axis) should show the values of the condition that has been changed (the independent variable). The Y axis (vertical axis) should show the measurements that were taken (the dependent variable). In this way, someone looking at the table can tell what was done in the investigation. To make the graph easier to interpret, the values on the X and Y axes should be in numerical sequence (from lowest to highest value) and placed at an even distance apart. The numbers and the scale on the X axis do not need to be the same as on the Y axis, and rarely would they be.
- YouTube video: Scientific Variables
- Designing and running a fair test: assessment rubric
- Working Scientifically: investigation framework
- Balloon Powered Car: student video and instructions
Adjustments for the diversity of learners
Students determine whether there is a relationship between the number of wheel rotations and the speed that a balloon car travels. Students would need to devise a way of counting the number of wheel rotations.
The more mathematically inclined students could investigate the circumference of the circle forming the wheel, not by using a formula, but by estimation and measuring. A productive sequence for this would be:
- Estimate the circumference of the circle
- Use a piece of string to measure the circumference
- Estimate the length of the piece of string (thus the circumference)
- Measure the length of the piece of string
- Determine the best units for this measurement
- How accurate can this measurement be? (possibly introduce the idea of rounding up)
In using this mathematical method students could actually calculate how many rotations would be necessary to cover the distance travelled. This data would be best represented as a line graph. If this is done, one could then determine how many rotations would be completed by wheels of different sizes.
By completing this STEM activity students have been provided with the experience of planning and conducting a controlled, first-hand investigation which has generated data that can be used for analysis. The students recorded and manipulated this data in order to draw conclusions about their investigation.
Competent use of mathematics and data analysis will form the basis of success in a student’s study of Science, and these skills are essential for any scientifically and mathematically literate citizens.