Accuracy vs. Precision
After watching the video, check your understanding here: https://ed.ted.com/on/veo9upe5#review
A precise measurement is one where independent measurements of the same quantity closely cluster about a single value that may or may not be the correct value.
An accurate measurement is one where independent measurements cluster about the true value of the measured quantity.
Measurement Uncertainty - Types of Error
An experimental error causes a measurement to differ from its true value and there are two main types:
Systematic uncertainty: usually due to an incorrectly calibrated scale (zeroing).
Random certainty: arise in any measurement
Systematic uncertainty is also called systematic error; random uncertainty is also called random error.
The absolute uncertainty in a physical quantity a is represented by Δa and may be taken to the smallest scale division of the measuring instrument as a reasonable order of magnitude estimate, e.g. the millimeter marking on a ruler.
The relative (percentage) uncertainty in a physical quantity a is represented by: Δa/a x 100%.
Half range rule: we use the mean to get the best representative value from the readings and we use half the range of the readings to estimate the uncertainty.
An experimental uncertainty (absolute or relative/percentage) is only one estimate and should be quoted to one significant figure only.
Task 1: Physics 3 Workbook p. 4-7
Rules for measurement - Propagation of Uncertainties
When measurements are to be added or subtracted, add the absolute uncertainty values.
When measurement are multiplied and derived, add the relative uncertainty values.
When a measurement is raised to a power, multiply the relative uncertainty values by the power (question: how about the square root?)
Task 2: Physics 3 Workbook p.8 - 13
Practice these questions to make yourself familiar with these rules.
Task 3: Practical Workbook: Experiment 1 & Experiment 2 (p.16-17)