Edexcel IGCSE Maths 复习笔记 4.4.2 Speed, Density & Pressure - Harder

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