Students forget to provide the correct units with their numerical answers.
What is wrong with this student’s answer regarding the magnitude of acceleration?
“The acceleration of the rocket is 15 m/s.”
Make sure you know the SI units for the following:
Mistake #4: Line of Best Fit?
When drawing a line of best fit, students must identify and eliminate any outliers before determining the trend. In the diagram shown below, if a student does not recognise the outlier then he/she will draw an incorrect line of best fit (dotted line). However, once you remove the outlier from the trend, then you can draw a correct line of best fit (solid line).
Mistake #5: Confusion About Validitiy, Reliability and Accuracy?
When students are asked how you would improve the accuracy of your experimental results, they often reply with a statement such as “repeat the experiment many times”. Does this sound like you? If so, then expect to lose at 3 – 4 marks in your HSC Exam this year.
Here is an outline of the differences between validity, reliability and accuracy:
Technique used in pendulum experiment
Validity is how appropriate the pro cedure and materials are to achieve a desired experimental result.
Swinging the pendulum through small amplitudes to ensure the equation given could be applied.
Reliability is how repeatable the experment is. Do you get very similar results every time?
Starting and stopping the stopwatch at the extremes of the motion ensures more repeatability than trying to start and stop mid-swing.
Accuracy is how close the value calculated from the experiment is to the accepted true value.
Use of more precise measuring devices such as a data logger and a sensor would improve accuracy.
Mistake #6: Human Error Is Not a Valid Type of Experimental Error!
When students are asked about how to improve the reliability and accuracy of the experimental results, most state “reduce human error!” Human error is not a valid type of experimental error! The two types of experimental error explored in physics experiments are random and systematic errors.
Random errors are caused by unknown and unpredictable changes in the experiment, e.g. due to the instruments or environmental conditions. These arestatistical fluctuations in both directions about the true value thus repetition and statistical analysis can reduce the effects. To help reduce random errors:
Make sure you know how to read the scales on the instruments and that you align yourself properly each time you take a measurement.
Take multiple measurements (repetition increases reliability!) and then take an average for the result
Systematic errors are caused by measuring instruments being used incorrectly or problems with the instrument itself. Systematic errors limit accuracy. To help reduce systematic errors:
All instruments should be checked against a standard before use. Zero settings should be checked and adjusted (calibration!).
Instructions for the use of the instrument should be read and followed.
Corrections for instrument bias should be made (if necessary).
Written by DJ Kim
DJ is the founder of Matrix Education and has over 20 years of HSC Physics teaching experience. He is the co-author of the Matrix Science program, course materials and assessments. He is also renowned for his ATAR & Scaling seminars and development of the first ATAR Calculator.