Speed-Density-And-Pressure Wjec-Eduqas Foundation

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Exam code:C300

Speed, density & pressure

What are speed, density and pressure?

Speed, density and pressure are frequently used compound measures
- Speed is equal to distance divided by time
- Density is equal to mass divided by volume
- Pressure is equal to force divided by area

Formula Triangles for Speed, Density and Pressure

What should I know about speed, distance and time?

Speed is commonly measured in metres per second (m/s) or kilometres per hour (km/h)
- The units indicate speed is distance per time
  $Speed equals Distance over Time$
‘Speed‘ (in this formula) means ‘average speed‘
In harder problems there are often two journeys or two parts to one longer journey

What should I know about density, mass and volume?

Density is usually measured in grams per centimetre cubed (g/cm³) or kilograms per metre cubed (kg/m³)
- The units indicate that density is mass per volume
  $Density equals Mass over Volume$

You may need to use a volume formula to find the volume of an object first

What should I know about pressure, force and area?

Pressure is usually measured in Newtons per square metre (N/m²)
- The units of pressure are often called Pascals (Pa) rather than N/m²
- The units indicate that pressure is force per area
  $Pressure equals Force over Area$
Remember that weight is a force
- It is different to mass

Examiner Tips and Tricks

Look out for a mixture of units
- Time can be given as minutes but common phrases like ‘half an hour’ (30 minutes) could also be used in the same question
- Any mixed units should be those in common use and easy to convert, e.g., g to kg or m to km etc

Worked Example

A box exerts a force of 140 newtons on a table.
The pressure on the table is 35 newtons/m².

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F space equals space force
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Maths Gcse Wjec-Eduqas Foundation