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”

SDT Triangle You have seen this in Science? s d t x

d s t x = d = s x t = d ÷ s t Speed? Time? Distance? We can use this to find any one thing IF we know the other two! s d t x By covering up what you want Speed? Time? = d t = s x t Distance? = d ÷ s

A train travels 120 miles in 2 hours What is its average speed? mph s d t x MUST give UNITS MILES per HOUR

d s t x =s x t d = 8 x 25 Distance d = 200 metres A runner’s average speed is 8m/s, how far does he run in 25 seconds ? d = 8 x 25 Distance =s x t d = 200 metres s d t x MUST give UNITS Because speed was in METRES per second

Because speed was in km per HOUR A lorry leaves Stoke, travels 150km to Leeds at an average speed of 60km/h. How long did the journey take? t = 150 ÷ 60 Time = d s t = 2.5 hours s d t x MUST give UNITS Because speed was in km per HOUR

Car travels 40km in 20 minutes. What is its average speed in kph? s = 120kph s d t x

Density – Mass - Volume Part 2

What is Density? Weight of a given amount of a material Density = Mass ÷ Volume

DMV Triangle You have seen this in Science? d m v x

m d v x = d x v = m v = m d Mass? Density? Volume? We can use this to find any one thing IF we know the other two! d m v x By covering up what you want = d x v Mass? Density? Volume? = m v = m d

Kilograms per Cubic Metre A steel girder weighs 2500 kg and has a volume of 100m3 What is its density? d = 2500 ÷ 100 Density = m v = 25 Kg/m3 d m v x MUST give UNITS Kilograms per Cubic Metre

Population Density Part 3

People per Square Kilometre A town in S France has a population of 120,000 living in an area of 15km2 What is the population density? d = 120 000 ÷ 15 Population density = p a people / km2 d = 8000 d p a x MUST give UNITS People per Square Kilometre