What are speed, density and pressure?

• Speed,?density?and?pressure?are compound measures – they are made from other measures
  • Speed?is related to the measures?distance?and?time
  • Density?is related to?mass?and?volume
  • Pressure?is related to?force?and?area

   

• The relationship between each of these sets of measures follows the same pattern – what we refer to as “blue triangles”

• If you do not remember the blue triangles – do not worry, these can often be deduced from information given in the question – see the examples below
• It is important you understand and can do the basic questions with speed, density and pressure

Speed, distance and time harder problems

• Speed?is commonly measured in?metres per second?(m/s) ormiles per hour?(mph)
  • There are other possibilities such as?kilometres per hour?(kmph)
  • The units indicate?speed?is?distance per timeie?speed = distance ÷ time

   

• “Speed” (in this formula) means “average?speed”
• In harder problems there are often two journeys – or two parts to one longer journey

Density, mass and volume harder problems

• Density is usually measured in?grams per cubic centimetre?(g/cm³)or?kilograms per cubic metre?(kg/m³)
  • The units indicate that?density?is?mass per volume 

    ie?density = mass ÷ volume

   

• In harder problems there are often two metals (alloys), liquids or gases that have been combined rather than working with a single substance

Pressure, force and area harder problems

• 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 

    ie?pressure = force ÷ area

   

• Remember that?weight?is a?force;?it is different to?mass