1. Mechanics Measurement
A physical quantity is a quantity that can be measured.
Examples of physical quantities are
Length
Mass  
Temperature
Time and
Energy  .
Every physical quantity has a numerical size and a unit. All units must be written, even in intermediate working.
Example: 15 m + 12 m = 27 m.
               (Not: = 27 m)

2. Mechanics Measurement SI Units
Scientists around the world agree to use the SI units for measuring physical quantities.
The SI units for all other physical quantities can be expressed in terms of these base quantities.
Fundamental Quantity
SI Unit
Symbol
Length
Metre m
Mass
Kilogram kg
Time
Second s
Temperature
Kelvin K

3. Mechanics Measurement Examples:
Volume of a cube = length x length x length
Hence, SI unit of volume = SI unit of length x SI unit of length x SI unit of length
                                          = m x m x m
                                         = m3.
Density = Mass / Volume
Hence, SI unit of density = SI unit for mass / SI unit for volume
                                        = kg m -3

4. Mechanics Measurement Prefixes
Prefixes allow scientists to write the size of very large or very small physical quantities easily.
Example
15 km = 15 × m = m
Prefix
Symbol
Meaning
Mega- M
Kilo- k
1 000
Milli- m
1 / 1 000
Micro
1 /

5. Mechanics Measurement Scientific Notation – Standard Form
The velocity of light in a vacuum is ms-1 = x 108 ms-1
The wave length of violet light is m = 4.2 x m
Standard form is used
to abbreviate numbers with a large number of digits
To do quick comparisons of value by comparing their powers of 10
Eg The mass of the sun is 1.99 x 1030 kg
The mass of Jupiter is 1.90 x 1027 kg
The mass of the sun is approximately
= 103 = times that of Jupiter

6. Mechanics Measurement
To see how to do the previous calculation of a scientific calculator, click here

7. Mechanics Measurement Systematic Errors
All Experiments contain errors. Some of these errors are related directly to the instruments used. Here are some examples,
Parallax error when using a ruler.

8. Mechanics Measurement Parallax error when using a measuring cylinder
Parallax error occurs when you place your eye at the wrong position and end up reading at an angle.

9. Mechanics Measurement
Other systematic errors that can occur in experiments are:
Friction
Reaction Time Error
Zero Error (instruments not being set to zero correctly)
These errors are fixed and can be allowed for
Instruments used to measure length
Instrument
Used to measure
Precision
Tape Measure
> 1 m
1 mm
Metre Rule
10 cm to 1 m
Vernier Caliper
20 mm to 100 mm
0.1 mm
Micrometer
0 mm to 25mm
0.01 mm

10. Mechanics Measurement Calculating with Measured Values:
Rule 1: When ADDING or SUBTRACTING measurements, round the answer to the smallest number of decimal places
Rule 2: When MULTIPLYING or DIVIDING measurements, round the answer to the smallest number of significant figures.
4.7 m m m
kg kg
18.24 m x 6.43 m
m / 7.02 s
= m
= kg
= 117 m2
= ms-1

11. Mechanics Measurement
There is also uncertainty in measurements because of the accuracy of the device you are using.
Measurements on a metre rule would be to ± 1mm

12. Mechanics Measurement Watch a video on how to use Vernier Callipers

13. Mechanics
Measurement

14. Mechanics Measurement Watch a video on how to use

15. Mechanics
Measurement

16. Mechanics Measurement Triple Beam Balance
Watch a video on how to use a triple beam balance

17. Mechanics Measurement
Example: Find the volume of a microscope slide by using suitable equipment to measure its length, width and thickness

18. Mechanics Measurement Example: Find the density of a marble
Use suitable equipment to find the diameter and the mass of the marble.
Density = Mass/Volume
Volume of the marble = 𝟒𝝅 𝒓 𝟑 𝟑 where r is the radius and is half of the diameter

19. Mechanics
Measurement