Measurements

Measurements

17 January 2023

14:34

If readings are precise we mean:

• 0.76

• 0.77

• 0.75

• 0.76

• 0.77

• 0.85

You can see 5 out of 6 of them are closer together. The odd one is 0.85 because it is not close to the others. When graphing we leave it out and that means the other readings are precise.

Accuracy is when you make sure to get the exact answer by re-measuring and finding average amongst measurements.

Density of water is 1000kg/m³ | 1 g/cm³

1,000,000

Mass and weight

• Mass

  • Nothing to do with gravity

  • Defined as the quantity of matter in an object

• Weight

  • A force

  • Quantity of matter contained by it given a downward force

  • Affected by gravitational pull on an object

• Weight = mass x gravitational strength

  • W = mg where g on earth = 10N/kg

  • Density of water is 1000kg/m³ | 1 g/cm³

     

    1,000,000

     

    Mass and weight

    • Mass

      • Nothing to do with gravity

      • Defined as the quantity of matter in an object

    • Weight

      • A force

      • Quantity of matter contained by it given a downward force

      • Affected by gravitational pull on an object

    • Weight = mass x gravitational strength

      • W = mg where g on earth = 10N/kg

     

    Textbook Chapter 1

     

    Measuring length and volume                                                                                                                

    Bigger and smaller

    Prefix	Meaning	Example
    G (giga)	1 000 000 000	GW gigawatt
    M (Mega)	1 000 000	MW megawatt
    k(kilo)	1000	km kilometre
    d (deci)	1/10	dm decimetre
    c (centi)	1/100	cm centimetre

SI units

Measuring volumes

• Two approaches

  • Regular shape

    • Measure sides of shape and multiply them together

      • Length x width x height

      • This is for something like a cube

    • Spheres, cylinders, anything similar

      • May need extra measurements to find the volume

  • Irregular shape

    • Liquids

      • Measuring cylinder can be used

Measuring volume by displacement

• Find measuring cylinder larger than the object

• Fill with water

  • Enough to immerse the object

• Record starting volume without object inside

• Put object in water

• Water level will increase

• Record the amount it increased

• Subtract the increased by the starting

Unit of length and volume

• 1 l = 1 dm³

Improving precision in measurements                                                                                                                       

Vernier callipers

• Two scales

  • Main

    • Divided in to millimetres

• Stationary

• Vernier

  • 9mm longer

  • Moveable

• Distance between the two inner jaws

• Close jaws lightly but firmly on side of object being measured

• Look at 0 on vernier

• Read main scale just to the left of the 0 on the vernier

• On the vernier scale, find where it is exactly in line with one marking

• Read value

  • Tells value of a fraction of a millimetre that you must add to main scale reading

    • Main scale + vernier reading

    • 35mm + 0.7mm

    • 35.7mm

Micrometre screw gauge

• Two scales

  • Main scale on shaft

  • Fractional scale on rotating barrel

    • 50 divisions

      • One complete turn is 0.50mm

• Turn barrel until jaws tighten

• Ensure just the right pressure

• Read main to nearest 0.5mm

• Read additional fraction of a millimetre on fractional

  • Main + fractional

  • 2.5mm + 0.17mm

  • 2.67mm

Density                                                                                       

• Property of a material

• How concentrated mass is

• Ratio of mass to volume

• Mass is in grams

• Volume is in cm³ or cubic centimetres

  • Space an object takes up

• Density is in g/cm³ or grams per cubic centimetres

Values of density

• Gas have lower density than both solids and liquids (obviously)

• Gold denser than silver

• Density is key to floating

• Ice floats in water because it's less dense

  • Icebergs

• Some woods are less dense and make them float while others may sink

• Mahogany more dense

• Depends on composition

Calculating density

• Need to know mass and volume

  • Divide volume from mass

Measuring density

• Regular shape

  • Mass using balance

  • Find its volume

  • Calculate

• Irregular shape

  • Find volume of water

  • Place object in water

    • You will have a starting and ending volume

  • Subtract ending from starting volume

  • Find mass and use density calculating formula

• A liquid

  • Place measuring cylinder on balance

  • Set to 0

  • Pour liquid

  • Record

• You can use a hydrometer

  • The scale indicates relative density

    • Compared with water density

    • Reading of 1.05 means 1050kg/m³

Measuring time

• In a race even a fraction of a second determines a lot

• Stopwatches commonly used in science experiments

  • To check the temperature of something changes over time

• Stop clocks/stopwatches

  • Analogue

    • Traditional

    • Hands moving around clock face

    • Making accurate short time recordings can be difficult

• Human error

• Takes you time to react to stop

• Digital

  • Direct reading in numerals

  • Buttons for different things

    • Starting time

    • Stopping tie

    • Resetting to zero

• A way to record to avoid human error

  • Using a pendulum

• Every swing is called a period

  • If you let a pendulum swing for 10 times, find that time recorded and divide it by 10

  • Time for 10 swings = 55s

  • 1 swing is 55/25 = 2.2s