SIS in Physics

Date: 2023-02-07

The Basics

• Accuracy is how close our measurement is to the actual/real value
  • When describing, things are not ‘reasonably accurate’ - they are either accurate or not accurate
  • $\pm 5\%$
• Precision in terms of a measuring instrument, is the fineness of the scale on the instrument
  • A property of the instrument itself
  • We use experimental precision - how far apart from average experimental value
• Reliable  - when additional trials give a consistent result
• Validity occurs when every variable is controlled as you intend it - no other variable is having an impact on our experiment other than the deliberate experimentation of the independent variable and the resulting response of the dependant variable.

Uncertainty & Error

• 3 Classes
  • Measurement error - unavoidable, property of the measuring instrument
    • Absolute Error - of the instrument, $= \frac{1}{2}$ of the smallest unit of scale on the instrument - e.g. 30cm ruler with millimetre increments = 0.5mm. So whatever value you get would be $n\pm 0.5mm$             - Percentage Error - this is $(\frac{absolute \space error}{measurement}*100)\%$
    • Systematic error - affect the results such that all measurements are skewed away from some ideal value sought
    • Random - affect the results in a way which, if truly random, tend to cancel each other out

Examples: the error for 10cm on a 30cm ruler is 0.5% the error for 15cm on a 30cm ruler is 0.33% the error for 21cm on a 30cm ruler is 0.24%

When multiple measurements are involved, you do different things depending on how they are related.

• When you add measurements together, you add the absolute errors together.
• When you multiply measurements together, you add the percentage errors together.