MEASURING AND CALCULATING

Chapter 2

TYPES OF PROPERTIES

There are two ways to describe our world:QuantitativelyQualitatively

A quantitative property is one that you can measure with a number.

An example would be 3 miles or 100 degrees C

A qualitative property is one that does not have a number.It is described without measurement

Examples of this would be that wood is brown or it is cold outside.

MEASURING DISTANCEWhat is a measurement?

A measurement is an exact value that tells you “how much”.

It is important that a measurement can communicate an amount in a way that other people can understand.

45Is this a measurement?It is not a measurementAre we talking about apples or kiwis?

MilesIs this a measurementThis is not a measurementIs there half a mile or 100 miles?

Every good measurement gives a quantity and a unit.

A unit of measurement is a standard amount of a quantity

What separates a good unit from a bad unit?

ActivityDirections: Part 1: One at a time, everyone take your right hand and measure how many “hands” it takes to go around one lab bench.

1 hand is from the tip of your longest finger to the bottom of your palm.

Part 2: Using your own feet, measure how many feet it takes to get from the teachers desk to lab station 5.

Put your results on the board.

Before measurement was standardized, the king where you were living would make measurements.

A foot was how long the kings foot was.

A cup was how much water the kings favorite cup could hold.

Now imagine living in medieval France, and the king of Spain ordered 500 cups of wine. How could this cause a problem?

Distance is the amount of space between two points.

The space between you and your friend, or the space between your house and the school are all distances

Distance is measured in unites of length.Distance and length are interchangeable

Some examples of length are inches, miles, centimeters or kilometers.

TWO SYSTEMS OF MEASUREMENT

These two systems are called the English System and the metric system.

Only 3 countries in the world still use the English system

Liberia, Myanmar, and USA

Another name for the metric system is the International System of Units

This can be abbreviated to SIAlmost all of science is measured using SI units.

This is because everything is measured in factors of 10.

1 kilometer = 1,000 meters1 meter = 100 centimeters = 1000 millimeters

In this class, we will be using the metric system the most often but will occasionally use the English system.

MEASURING TIMEThe word time can have two meanings.

It can be an exact moment or it can be a duration.

When you ask for the time, you want to know an exact moment.

You then proceed to identify this moment by checking a clock.

You may also ask “how much time?”

For this you need a time interval.

A time interval is a quantity of time that has a beginning and end.

In this class, time will mostly be a time interval and measured in seconds.

Time is usually represented by the variable t

The second is used in both the English and metric system.

Most often in science, we will time an event in seconds, but sometimes we will have to consider a fraction of a second.

How much time is 3:27:41?3 Hours, 27 minutes, and 41 seconds

How many total seconds is this?

12461 seconds

Most commonly people give time in mixed units.Hours, minutes and seconds

In science, the time can only have one unitUsually seconds

MASS AND WEIGHTChemistry is based off of the study of matter.

Often it will be important to know how much matter there is.

The typical household scale has a spring in it.

When you step on the scale, the spring gets compressed (squished)

The scale then measures how compressed the spring is and tells you how many pounds you weigh.

What is the scale measuring?

It is not measuring how much “stuff” you are made of.

Rather, it measures the pull of gravity on you.

Weight is a measure of the force of gravity between two objects

Why is this not the best way to measure an amount of matter?

If gravity changes, then weight changes

In science, we need a measurement that does not change.

This time lets use a balance.

You stand on one end, and bricks are put on the other end until the balance is level.

You know that each brick weighs 1kg so you know how many kilograms you are.

Is this a better measurement? Why?

When gravity changes for you, it will also change for the bricks.

This means you are measuring an amount of matter and not the pull of gravity.