Quantities and units

International System units, scalars and vectors, and conversions useful in sport.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

International System (SI): what is it?
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The set of reference units: metre, kilogram, second, newton, joule, watt…
Calculating in SI avoids most errors.
A calculation mixes km/h and seconds. What should be done first?
- Convert everything to SI units
- Multiply the km/h by 3.6
- Convert the seconds to minutes
- Round the km/h to the nearest ten
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Convert everything to SI units
Consistent units give a correct result: in SI, km/h are divided by 3.6 to give m/s.
Scalar: what is it?
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A quantity fully described by a number and a unit: mass, time, distance.
It has no direction.
Why is velocity a vector?
- It is measured in metres per second
- It has a direction as well as a magnitude
- It changes during every movement
- It is always positive or zero
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It has a direction as well as a magnitude
Running at 5 m/s north or south is not the same velocity.