Compound Measures OCR Stage 6 Speed Distance Time

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? d s x t

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

A train travels 120 miles in 2 hours What is its average speed? s = 120 ÷ 2 s = 60 mph MUST give UNITS MILES per HOUR Speed = d s x t d t

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

A lorry leaves Stoke, travels 150 km to Leeds at an average speed of 60 km/h. How long did the journey take? t = 150 ÷ 60 t = 2. 5 hours MUST give UNITS Because speed was in km per HOUR Time =d s x t

Car travels 40 km in 20 minutes. What is its average speed in kph? s = 40 ÷ 1/3 Speed = s = 120 kph d s x t d t

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? m d x v

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

A steel girder weighs 2500 kg and has a volume of 100 m 3 What is its density? d = 2500 ÷ 100 = 25 Kg/m 3 MUST give UNITS Kilograms per Cubic Metre Density = m v m d x v

Population Density Part 3

A town in S France has a population of 120, 000 living in an area of 15 km 2 What is the population density? d = 120 000 ÷ 15 Population density 2 =p people / km d = 8000 a MUST give UNITS People per Square Kilometre p d x a