Compound Measures

OCR Stage 6

Speed - Distance - Time

Part 1

What is speed?

• How far you travel in a certain time• Speed = Distance ÷ Time• We call the result “the average speed”

tds

SDT Triangle

sd

tx

You have seen this in Science?

sd

tx

We can use this to find any one thingIF we know the other two!

By covering up what you want

Speed? = d t

Distance? = s x tTime? = d ÷ s

A train travels 120 miles in 2 hoursWhat is its average speed?

sd

tx

= d t

Speeds = 120 ÷ 2s = 60 mph

MUST give UNITS

MILES per HOUR

A runner’s average speed is 8m/s, how far does he run in 25 seconds ?

sd

tx

=s x tDistanced = 8 x 25d = 200 metres

MUST give UNITS

Because speed was in METRES per second

A lorry leaves Stoke, travels 150km to Leeds at an average speed of 60km/h. How long

did the journey take?

sd

tx

= d s

Timet = 150 ÷ 60t = 2.5 hours

MUST give UNITS

Because speed was in km per HOUR

Car travels 40km in 20 minutes. What is its average speed in kph?

sd

tx

= d t

Speeds = 40 ÷ 1/3s = 120kph

Density – Mass - Volume

Part 2

What is Density?

• Weight of a given amount of a material• Density = Mass ÷ Volume

vmd

DMV Triangle

dm

vx

You have seen this in Science?

dm

vx

We can use this to find any one thingIF we know the other two!

By covering up what you want

Density?= m v

Mass? = d x vVolume? = m d

A steel girder weighs 2500 kg and has a volume of 100m3

What is its density?

dm

vx

= m v

Densityd = 2500 ÷ 100Kg/m3

MUST give UNITS

Kilograms per Cubic Metre

= 25

Population Density

Part 3

A town in S France has a population of 120,000 living in an area of 15km2

What is the population density?

dp

ax

= p a

Population densityd = 120 000 ÷ 15people / km2

MUST give UNITS

People per Square Kilometre

d = 8000