Lim Yang Kiow

Monday, 5 December 2011

Adding and Subtracting Time

Add or Subtract the hours and minutes separately.
But you may need to do some adjusting if the minutes end up 60 or more, or less than zero!

Adding Times

Follow these steps:

Add the hours
Add the minutes
If the minutes are 60 or more, subtract 60 from the minutes and add 1 to hours

Like this:

Easy example: What is 2:45 + 1:10 ?

Add the Hours: 2+1 = 3
Add the Minutes: 45+10 = 55

The minutes are OK, so the answer is 3:55

Hard example: What is 2:45 + 1:20 ?

Add the Hours: 2+1 = 3
Add the Minutes: 45+20 = 65

The minutes are 60 or more, so subtract 60 from minutes (65-60 = 5 Minutes) and add 1 to Hours (3+1 = 4 Hours) ... so the answer is 4:05

Subtracting Times

Follow these steps:

Subtract the hours
Subtract the minutes
If the minutes are negative, add 60 to the minutes and subtract 1 from hours.

Like this:

Easy example: What is 4:10 - 1:05 ?

Subtract the Hours: 4-1 = 3
Subtract the Minutes: 10-5 = 5

The minutes are OK, so the answer is 3:05

Hard example: What is 4:10 - 1:35 ?

Subtract the Hours: 4-1 = 3
Subtract the Minutes: 10-35 = -25

The minutes are less than 0, so add 60 to Minutes (-25+60 = 60-25 = 35 Minutes) and subtract 1 from Hours (3-1 = 2 Hours) ... answer is 2:35

Sunday, 4 December 2011

Clocks

Clocks

In our world we have digital clocks (they have digits like 0,1,2,3) ...

... and analog clocks (they have hands) ...

Digital Clocks

Digital Clocks show us the time using numbers. The number on the left of the : is Hours, and the number on the right is Minutes:



5 Hours and 8 Minutes		9 Hours and 36 Minutes

Clocks with Hands

Clocks can also use hands to show us the Hours and Minutes. We call them "analog" clocks.

The Little Hand shows the Hours:


Hours		5 Hours

The Big Hand shows the Minutes:


30 Minutes or Half-Past		15 Minutes or Quarter-Past

Using both the Big Hand and Little Hand lets us know exactly what time it is:


2:30 or Half-Past Two		5:15 or Quarter-Past Five

Metric Mass (Weight)

Mass: how much matter is in an object.

We measure mass by weighing, but Weight and Mass are not really the same thing.

These are the most common measurements:

Grams
Kilograms
Tonnes

Grams are the smallest, Tonnes are the biggest.

Let’s take a few minutes and explore how heavy each of these are.

Grams

A paperclip weighs about 1 gram.
Hold one small paperclip in your hand. Does that weigh a lot? No! A gram is very light. That is why you often see things measured in hundreds of grams.

Grams are often written as g (for short), so "300 g" means "300 grams".

A loaf of bread weighs about 700 g (for a nice sized loaf)

Kilograms

Once you have 1,000 grams, you have 1 kilogram.

1 kilogram = 1,000 grams

A dictionary has a mass of about one kilogram.

Kilograms are great for measuring things that can be lifted by people (sometimes very strong people are needed of course!).

Kilograms are often written as kg (that is a "k" for "kilo" and a "g" for "gram), so "10 kg" means "10 kilograms".
When you weigh yourself on a scale, you would use kilograms. An adult weighs about 70 kg. How much do you weigh?

But when it comes to things that are very heavy, we need to use the tonne.

Tonne

Once you have 1,000 kilograms, you will have 1 tonne.

1 tonne = 1,000 kilograms

Tonnes (also called Metric Tons) are used to measure things that are very heavy.
Things like cars, trucks and large cargo boxes are weighed using the tonne.
This car weighs about 2 tonnes.

Tonnes are often written as t (for short), so "5 t" means "5 tonnes".

Final thoughts about measuring weight:

1 kilogram = 1,000 grams

1 tonne = 1,000 kilograms

Metric Volume

These are the two most common measurements:

Milliliters
Liters

A milliliter (that is "milli" and "liter" put together) is a very small amount of liquid.

Here is a milliliter of milk in a teaspoon.

It doesn't even fill the teaspoon!

If you collect about 20 drops of water, you will have 1 milliliter:

20 drops of water makes about 1 milliliter

And a teaspoon can hold about five milliliters:

1 teaspoon of liquid is about 5 milliliters

Milliliters are often written as ml (for short), so "100 ml" means "100 milliliters".

Here we have 150 ml of milk in a measuring cup.

It doesn't say "150" ... it says "50" ... but it is half-way between 100 and 200 so you can figure out it is 150 ml.

Liter

A liter is just a bunch of milliliters put all together. In fact, 1000 milliliters makes up 1 liter:

1 liter = 1,000 milliliters

This jug has exactly 1 liter of water in it.

Liters are often written as L (for short), so "3 L" means "3 Liters".

Milk, soda and other drinks are often sold in liters.

The next time you are at the store take a minute and look on the labels to see how many liters (or milliliters) are in each container!

Liter is abbreviated L (some people use lowercase l, but that looks too much like 1).

Another way of thinking about a liter is:

A box that is 0.1 meters (10 cm) on each side,
One square meter that is millimeter thick.

Other Volume Measurements

You may come across these other volume measurements:

Cubic Meter (m³)

Volume is length by length by length, so the basic unit of volume is a cube that is 1 meter on each side.

The Unit is written m³ (cubic meters).

So, a cube that is 1 meter on each side is a cubic meter (m³) ...

... and that is also equal to 1,000 liters.

1 m³ = 1,000 Liters

Megaliters (ML)

A Megaliter is a million liters (1,000,000 L). Useful for measuring large quantities of water, such as in lakes and dams.

Metric Length

Metric Length

You can measure how long things are, or how tall, or how far apart they are. Those are are all examples of length measurements.

Example: This fork is 20 centimeters long

These are the most common measurements:

Millimeters
Centimeters
Meters
Kilometers

Small units of length are called millimeters.

A millimeter is about the thickness of a plastic id card (or credit card).

Or about the thickness of 10 sheets of paper on top of each other.

This is a very small measurement!

When you have 10 millimeters, it can be called a centimeter.

1 centimeter = 10 millimeters

A fingernail is about one centimeter wide.

Two tape measures, one in mm, the other in cm

You might use millimeter or centimeters to measure how tall you are, or how wide a table is, but you would not use them to measure the length of football field. In order to do that, you can switch to meters.