Measurement + Units
Measurements in Physics
• The most important measurements in Physics are Length, mass and time
• To make sure everybody in the world can understand each other we all use the same units called SI units (Systeme Internationale)
SI units + SymbolsQuantity SI Unit Symbol Other
Units used
Length
Mass
Time
Area
Volume
SI units + SymbolsQuantity SI Unit Symbol Other
Units used
Length Metre m km, cm, mm,
Mass Kilogram Kg Gram (g)
Time Second S minute (min) Hour (h)
Area Square metre
m2 cm2, km2
Volume Cubic metre
m3 cm3, Litre (L)
Measuring lenght
• A metre stick or ruler measures straight lines
Opisometer
• An opisometer can be used to measure short curved lines for example a road or a river on a map
Trundle Wheel
• Used to measure long curved lengths for example around a flower bed
Vernier Callipers
• To find the diameter or width of a solid object for example marble or a piece of piping
• Click here to see how it works
Learning Check
• What units is length measured in?
• What units is mass measured in?
• What units is time measured in?
• How would you find the length of a short curved line?
• How would you find the distance from here to the shop?
Measuring Area
• Area is how much space something covers
• A book has a smaller area than a field• To get the area of a regular shape (a
square or a rectangle) multiply the length by the width
• Remember Area = L X W• Area is measured in metres squared m2
(or cm2 , km2 or mm2)
Measuring the area of an irregular object
• Your hand or a leaf does not have a regular shape
• To get the area of an irregular object trace it onto graph paper and count how many squares it covers, each square has an area of 1mm2
Mass
• Mass is the amount of matter in an object
• It is measured in the lab using an Electronic balance
• Usually measured in
Kg or g
Measuring Volume
• Volume tells you how much space something takes up
• It is measured in m3 (or cm3, ml or litres)
• For a regular object such as a cardboard box
Volume = Length X width X Height
Measuring volume of irregularly shaped objects
• A stone or a potato does not have straight edges, it is irregular
• We can measure the volume of irregular objects using a graduated cylinder and/or an overflow can