From Cubits to Kilometers!A Rule of Thumbs

In ancient Egypt, a carpenter couldn’t misplace his ruler because it was attached to his body.The units of length that he used were on his arm.

The cubit was the distance from the tip of his elbow to the tip of his middle finger.The digit was the width of one finger.These units fit together like this:

–Four digits equal one palm.

–Two palms equal one span.

–Two spans equal one cubit.

The units of length we use in the United States and England were once parts of the body too.

The foot was the length of a man’s foot.

The inch was the width of a thumb.

The yard was the distance from a man’s nose to the tip of his outstretched arm.

Measurement Standards

When a customer with long arms bought cloth from a merchant with short arms,

there were arguments about who should measure out the cloth.To avoid such arguments, people began using standard units.

In 1790, the French created a standard unit of measurement called the Metric System. Very few countries today don’t use this

International System of Measure!

The units of measurement for Length, Mass and Volume:Length meter (m)Mass gram (g)Volume liter (l)

Commonly used prefixes:

Prefix Meaning SymbolKilo 1000 k eg. 1 km = 1000mHecto 100 hDeka 10 da1Deci 0.1 dCenti 0.01 cMilli 0.001 m eg. 1mg = 0.001g or 1 g = 1000mg

One teaspoon is approximately 5 ml

20 drops is about 1ml

volume = W x L x Heg. 1cm x 1cm x 1cm = 1cm3 = 1ml

10cm x10cm x10cm = 1000cm3 = 1000ml = 1l

1l of water weighs 1 kg

What units would you use if I asked you to measure the width of one

piece of loose leaf paper?

• I measured 21.6cm What if I want to know how many mm this equals?

We need to use a conversion factor!

21.6 cm x _______ = mm

21.6 cm x _______ = mm 1cm

21.6 cm x 10 mm = mm 1 cm

21.6 cm x 10 mm = 216 mm 1 cm

What if we want to drive to Cape Breton for a visit and I tell you that we’re going to drive an average speed of 9500m/s. Does this make

sense?

9500m/s x _________ = km/s m/s

9500 m/s x 1 km/s = 9.5 km/s 1000m/s does this make sense?

9.5 km x 3600 s = 34 200 km s 1hr hr

Does this make sense? We should average under 100km/hr!!

Happy Trails to you……Happy Trails to you……

Problems to try…

• 3.2 m = ________mm

• 9.1 cm = _______m

• 26 kg = ________hg

• 16 L = __________mL

• 91km/hr = ___________m/s

• 36.2 m/s = ___________km/hr

• 612 m/s = ___________mm/min.

• 53 m/s = ___________m/h