What are the 7 SI Base units?
Mass kg
Length m
Time s
Current A
Temperature K
Amount of substance mol
Luminous intensity cd candela
Estimated Physical Quantities
Derived Units
Homogeneity of Physical Equations
The units on either side should be the same
Prefixes
Tera- 10^12
Giga- 10^9
Mega- 10^6
Kilo- 10^3
Centi- 10^-2
Milli- 10^-3
Micro- 10^-6
Nano- 10^-9
Pico- 10^-12
Displacement
Vector quantity
Describes how far an object is from where it started and in what direction.
Distance
Scalar quantity
Describes how far an object has travelled overall, but not the direction it has travelled
Combining vectors
Triangle method
Parallelogram method
Condition for Equilibrium
Coplanar forces can be represented by vector triangle.
In equilibrium, these are closed triangles. The vectors, when joined, form a closed path.
How to make an equation valid
- Check using experimental methods
- Lab instruments and Testing
Formula for calculating uncertainties
(d average+/- 1/2 range)unit
Systematic Error
When the measured value is always either larger than or smaller than the true value.
Random Error
Measured values are both larger and smaller than the true value in a random fashion
Sources of Systematic Error
1. Zero error: instrument has reading when nothing is measured
2. Incorrect calibration of instrument
Improvements of Systematic Error
!NOTICE! Cannot be done by taking repeated readings and average
(only helps with precision of reading)
1. True value= Reading - Zero error
2.Recalibrate instrument
Sources of Random Error
1. Human error: not suitable technique in set-up/instrument
2. Surrounding fluctuations: Temperature, pressure, refraction, friction...
Improvements of Random Error
1. Take several readings and average and find the mean value
(*improves BOTH precision and accuracy)
Parallax Error
occurs due to the incorrect positioning of the eye when taking a reading on a measuring scale
Anti-parallax Mirror
Wrong reading- pointer's image can be seen in mirror
Correct reading- pointer's image cannot be seen, is right behind the pointer
Difference between Systematic and Random Error
The Spread
-If the spread is only on one side, Systematic
-If the spread is on both sides, Random
Precision
Smallest division that can be measured by the instrument
(Decimal pt: smallest possible reading)
Accuracy
How close the values are to the true value
How to increase Precision
Taking average increases the precision by one d.p.
Define Power
work done / time taken
Formula for power and SI Unit
P=E/t