RANDOM OR NOT? INVESTIGATING PATTERNS IN REPEATING EVENTS

Published: Sep-2026 | Category: Secondary Science

A dripping tap can sound perfectly steady - until someone adjusts it. Traffic may arrive in clusters, even when the average flow appears consistent. How can we use recorded data to decide whether an event is regular, changing or genuinely unpredictable?

In this practical investigation, students mark each occurrence of a repeating event with a push button. EasySense records the event times, allowing them to look for patterns and use a line of best fit to compare regular and less regular sections of the data.

Learning objectives

By completing the activity, students can:

• record the timing of repeated events;
• identify regular and irregular patterns in a graph;
• use a line of best fit to analyse a selected region;
• interpret gradient and R² values in context; and
• explain why an irregular pattern is not automatically proof of randomness.

What do we mean by a random event?

A random count records how many times something happens when the exact result cannot be predicted in advance. Examples include the number of cars passing a point, calls received during an hour or wildlife sightings in a fixed area.

Individual events may be unpredictable, but a longer set of results can still contain useful patterns. Probability and statistics help us describe those patterns, compare different conditions and decide whether an apparent change is meaningful.

Equipment

• Wireless Push Button Switch Pack, including two push button switches and the Wireless Switch Sensor;
• connecting leads;
• a computer or compatible device running the latest release of EasySense2; and
• a repeating event that can be observed safely, such as water dripping from a tap or traffic viewed from a safe location.

Setting up the investigation

1. Connect the two push buttons to the Wireless Switch Sensor.
2. Open EasySense2 and connect to the sensor using the Devices icon.
3. Choose Timing mode and select Raw Data.
4. Select input A or B for the event marker.
5. Display event time on the Y-axis and reading number on the X-axis.

A dripping tap works particularly well because its rate can be kept steady and then deliberately changed. This creates sections that students can compare within the same recording.

Recording the events

1. Start recording in EasySense2.
2. Each time the chosen event is seen, press and release the selected push button as quickly as possible.
3. Continue long enough to collect a useful sequence of events.
4. If appropriate, change the rate part-way through the investigation. For example, gently adjust the tap and then allow it to settle at a new rate.
5. Stop the recording when the sequence is complete.

What should the graph show?

The reading number shows the order in which events occurred, while the event time shows when each one was recorded. If the gap between events stays constant, the plotted points should follow an approximately straight line.

The gradient of that line represents the time per event. For example, a gradient of 1 second per event indicates that one event occurred approximately every second.

If the intervals begin to vary, the points will move away from a straight-line pattern. A change in gradient may show that the event rate has changed, while a scattered or curved region suggests that the timing is less regular.

Using the Best Fit tool

Select a section of the graph and apply the Best Fit tool in EasySense2. The R² value describes how closely that selected data follows the fitted line:

• a value close to 1 indicates a strong straight-line relationship and therefore a consistent interval between events;
• a lower value indicates that the timings do not follow the straight line as closely; and
• different regions can be analysed separately to compare steady and disturbed behaviour.

In the worksheet example, the steady middle region gives an R² value of 0.999 and a gradient of 1 second per event. When the fit is extended beyond this steady region, R² falls to 0.834, showing that a single straight line describes the wider data less well.

It is important to be precise: a low R² value does not by itself prove that an event is random. It shows that the selected results are not well described by that particular straight-line model. Repeating the investigation and collecting more events gives stronger evidence.

Building data-handling skills

This activity gives students practical experience of:

• connecting a wireless sensor to EasySense2;
• collecting raw timing data;
• selecting and comparing regions of a graph;
• using Best Fit, gradient and R² values;
• changing the graph scale to inspect shorter time intervals; and
• distinguishing an observation from the conclusion drawn from it.

Questions for students

• Which section of your graph appears most regular, and what evidence supports your answer?
• What does the gradient tell you about the rate of the event?
• How does the R² value change when you analyse a steady region and then the whole recording?
• Could variation have been caused by the observer pressing the switch rather than by the event itself?
• What additional data would you collect before describing the event as random?

Ways to extend the investigation

Students could repeat the activity with traffic, pendulum passes or another observable event. They could compare different time periods, observers or conditions, or divide a longer recording into equal time intervals and count the events within each interval.

For older students, these counts can introduce probability distributions. The Poisson distribution may be considered when independent events occur at an approximately constant average rate, while the binomial distribution is useful for a fixed number of trials with two possible outcomes.

Practical considerations

• Use the same observer and the same press-and-release technique throughout each run.
• Record enough events to reveal a pattern and repeat the investigation where possible.
• Choose a recording rate that captures each event clearly without confusing the data.
• Keep the sensor, switches and device away from splashes when observing a dripping tap.
• Observe traffic from a secure position away from the road and never require students to stand near moving vehicles.

From everyday events to useful evidence

Repeated events often feel random when we experience them one at a time. By recording when they happen, graphing the results and testing how well a line fits the data, students can replace an impression with measurable evidence.

Download the full activity

The complete worksheet includes the apparatus and EasySense2 setup, student method, discussion questions, example graphs and teacher and technician notes.

Find and download the worksheet in Practical Explorer