measurements units

Measurements and Units

Quantities and Units


Form sentences with these quantities:

3m2

65km/h

1.76m

Physical Quantities are measurable and have physical (feel, see…) meaning.


4.5 m

Numerical Value

Unit


There are many units for each quantities

Example - Length: metres, centimetres, kilometres, feet,

inches, miles, nautical miles, light year

Only one of the many is an SI unit


Quantity SI Unit Symbol

Length Metre m

Mass Kilogram kg

Time Second s

Temperature Kelvin K


SI units for some other quantities.

When solving questions involving quantities. These quantities must have the same unit.

Quantites Unit

speed m/s

area m2

volume m3

density kg/m3

Quantities and UnitsExample 400 cm3 of water is added to 1 litre

of water. How much water is there?

Incorrect: 400 + 1 = 401cm3

Correct: 1 litre = 1000cm3

400 + 1000 = 1400 cm3


Very small numbers may have prefixes to make writing them easier.

Example

2 000 000 000 Byte = 2 GByte 0.000045 m = 45 m


Prefix Value Symbol

Giga One billion G

Mega One million M

Kilo One thousand K

Deci One tenth d

Centi One hundredth c

Milli One thousandth m

Micro One millionth µ

nano One billionth n

Conclusion

Numerical values and units give quantities meaning.

Only quantities that have the same units can be added or subtracted.

Prefixes may be added to very small quantities.

measurements units

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