Class Activity
What you will need:
- Measuring tapes (a few different ones if available)
- A student volunteer
- Small pieces of paper for each student
Instructions
1. Make sure each student has a ruler of some sort (in centimetres) and a small piece of paper to record their measurement.
2. Each student is to take turns measuring the student's arm length as accurately as possible and write down on a piece of paper without comparing with anyone else's results.
3. The teacher is to collect all the results and display them to the class.
Discussion questions in class
- What could be the reason for the differences in results?
- Are there any results that suggest a mistake was made by the measurer?
- Are there any results that suggest that there might be a problem with the ruler?
Error in Measurement
Error in measurement doesn't mean that it is wrong. Error refers to the accuracy of the measurement taken, that is how close to the true value your measurement is. It depends on a number of factors and the goal is always to get as close to the true value as possible.
Types of Errors in Measurement
Sources of error in measurement can be categorised as systematic errors, random errors, or blunders.
1. Systematic Error
Systematic errors are usually due to identified causes and can be avoided. There can be 3 kinds:
- Instrumental: a problem with the measuring instrument, for example calibrating scales.
- Observational: These errors occur due to a mismatch between a line of vision of the observer and the pointer above the instrument scale. This is also known as "parallax error".
- Environmental: external conditions that influence the measuring instrument or the space, for example, temperature, humidity, magnetic fields.
Discuss: What are some possible systematic errors in our measurement?
What is the absolute error of the measurements given the measuring tapes used?
Are most of the measurements within the limits of accuracy of each other?
2. Random Error
Random errors are named so because the causes are harder to identify. They are often small fluctuations that vary from one measurement to another. For example, if you were to measure the time it takes for an object to drop, your reaction time in starting and stopping the stopwatch will vary slightly each time you repeat the experiment.
Discuss: What are some possible random errors in our measurement?
3. Blunder
Blunders are outright mistakes. These errors are usually quite obvious. A person may record a wrong value, misread a scale, forget a digit when reading a scale or recording a measurement.
Discuss: What are some possible blunders in our measurement?
How can we minimise these types of errors to get close to the true measurement?