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