compound measures.ppt
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Transcript of compound measures.ppt
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