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

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

What are speed, density and pressure?

  • Speeddensity 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”

 

6.3.2-SDPHard-Notes-fig1

 

  • 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

 

6.3.2-SDPHard-Notes-fig2

 

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

 

6.3.2-SDPHard-Notes-fig3

 

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

 

Exam Tip

Do look out for a mixture of units:

  • Time can be given as minutes but common phrases like “half an hour”(ie 30 minutes) could also be used in the same question.
  • Any mixed units should be those in common use and easy to convertg to kg (and vice versa)

    m to km (and vice versa)

 

 

Worked Example

6.3.2-SDPHard-Example-fig1-sol

Worked Example

6.3.2-SDPHard-Example-fig2-alt-sol

转载自savemyexam

更多IGCSE课程
翰林国际教育资讯二维码