“Different units for different purposes”

(1) Length

How long is a Scottish midge?

11.5 mm inch

16

Units of length

0 1 cm

1 inch

= 2.54 cm

12 inches

= 30.48 cm

1 foot

1 foot0 2 feet 3 feet

1 yard 1 m

0

1 mile

= 1760 yards

=1600 m

1 mile

2= 880 yards

= 800 m

1 km

= 1000 m

1 mile = 1 furlong

8220 yards

= 200 m

5 mile

8

1 nautical

mile =

6080 feet

=1.85 km

Some approximate lengths

1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 m = 3.2808 ft

Height of a man 6 feet = 1.8 m

Length of a car 12 feet = 3.6 m

Height of a house 25 feet = 7.5 m

Length of a coach 42 feet = 13 m

Length of the swimming pool 82 feet = 25

m

5 miles = 8 km

For huge distances, we can use standard form

• 1 light year = 6 million million miles = 6×1012 miles = 9.4×1015 metres

Distance to nearest star (apart from Sun) = 4.2 light years= 4×1016 metres

You don’t need to remember this!!!

Converting length units

• We know 5 miles = 8 km, hence:

•

“100 times as far”

•

“Twice as far”

500500 miles = 8 km = 100 8 km 800 km

5

1616 km = 5 miles = 2 5 miles 10 miles

8

5 miles16 km = 16 km = 10 miles

8 km

the “unit multiplier”