Chapter: Measurement

Table of Contents

Section 1: Description and

Measurement

Section 2: SI Units

• *Section 1 – Description and

Measurements

• Measurement is a way to describe the world with numbers.

• What sort of measurements do you do in real life?

Measurement

Weight, quantities ,costs, distances,

periods of time….

Important:

*Measurements of a single item

might vary depending on the

measuring device you are using.

*In science, it is important to execute your measurements very carefully so you can trust the information

*Good part of the data you collect in experiments are the result of measurements

Measurement

• Estimation- it is a rough measurement

Estimation

Description and Measurement

• It is a skill based on previous knowledge

• For example, doorknobs are about 1 m above the floor

Figure 3 - page 44

See page 44 of the text book, figure 3

Read and think about your answer.

When do we use estimation?

When we don’t need to know the exact

measurement.

• Sometimes we need to know the exact

value:

• Then we will perform a measurement

USING TOOLS

• How do we know if our measurement

was properly done?

• Precision and accuracy – book pg 46

*Precision x Accuracy

Accuracy - compares a measurement

to its true value

If the measurement is close to the

actual value – this measurement is

accurate

*Precision x Accuracy

Precision - you are precise when you

measure something several times and

obtain always the same value, or very

close.

Precision and Accuracy

• Your house is 3 Km far from your school.

Suppose you measure the distance between your home and your school five times and obtain five measurements equal to 2.5 km.

Are you being precise or accurate? Precise

Precision and Accuracy

• Your house is 3 Km far from your school.

Suppose you measure the distance between your home and your school five times and obtain five measurements equal to 3 km.

• Are you being precise or accurate?

Both!!!!!!!!!!!!!!!!!!!

• Section 2 – SI Units

SI stands for International System

of Units

IMPORTANT:

• Communication is very important in

science.

• How do scientists in different countries

with different measurement systems

communicate and compare their

experiment results???

In 1960:

scientists decided to use an agreed-upon

standard of measurement known as

International System of Units (SI) ( also called

Metric System)

Why is it better?????

Advantages of using a common

system of measurement in Science

Facilitates the exchange, understanding

and comparison of scientific data

Advantages of using the metric

System

It is and easier system.

The SI units are related by multiples of

ten, so they are easier to use.

• The SI units are related by multiples of ten, so they are easier to use.

SI Units Prefixes used in measurements –

Not all are used on our daily

lives.

More frequently used are:

Kilo, centi, milli, micro, nano

+ the word meter

Or liter

Or gram

SI Units frequently used

Length - Kilometer, meter, centimeter

Mass - Kilogram, gram, milligram

Volume – liter, millimeter

Conversion factors

1) A conversion factor are used to convert

one unit into another.

2) In the metric system any value can be

converted into a smaller or larger number

by multiplying or dividing by a power of 10.

Most used units and conversions - length

1Kilometer (Km) equals 1000 meter (m)

1meter (m) equals 100 centimeters (cm)

Conversion:

• m to km divide by 1000

• Km to m multiply by 1000

• cm to m divide by 100

• m to cm multiply by 100

Most used units and conversions - volume

1 liter (l) equals 1000 milliliter (ml)

Conversion:

• ml to l divide by 1000

• l to ml multiply by 1000

Most used units and conversions - mass

1 Kilogram (kg) equals 1000 grams (g)

Conversion:

• g to Kg divide by 1000

• Kg to g multiply by 1000

Distance ( Km, m, cm)

1 kilometer Equals 1000 meters

1 meter Equals 10 decimeters and 100

centimeters, 1000 millimeter

1 decimeter Equals 10 centimeter

1 centimeter Equals 10 millimeters

Millimeter

Volume ( liter and milliliter)

1 liter 1000 milliliter

Milliliter 1/1000 liter

Mass ( kilogram or grams)

Kilogram Equals 1000 grams

Gram Equals 1000 milligrams

Milligram Equals 1/1000

• The meter (m) is the SI unit of length. One meter is about the length of a baseball bat.

Length

• Length is defined as the distance between two points.

SI Units

Length

SI Units

2

• Smaller objects can be measured in centimeters (cm) or millimeters (mm). A pencil would be measured in cm .

• Long distances – from one city to another –would be measured in Km.

When using a ruler, make sure

to start from 0

SI Units

Volume

• The amount of space an object occupies is its volume. The cubic meter (m3) is the SI unit of volume.

SI Units

Volume

SI Units

• To find the volume of a regular object, such as a brick or your textbook, measure its length, width, and height and multiply them together.

Volume = length x width x height

*Volume of liquids

SI Units

• *For this type of measurement, the tool you use is a graduated cylinder.

• It is important to read the base of

the meniscus.

Volume by Immersion or Displacement

• Some objects have an irregular shape.

SI Units

• When you measure the volume of an irregular object, you start with a known volume of water and drop in, or immerse, the object.

• The increase in the volume of water is equal to the volume of the object.

Volume by Immersion or

Displacement for Irregular Solids

What is the

volume of the

stone????

Mass

• The mass of an object measures the amount of matter in the object.

SI Units

• The kilogram (kg) is the SI unit for mass.

• You can determine mass with a balance.

Digital scale

Weight

Weight and mass are not the same.

Mass depends only on the amount of matter in an object.

Weight is the amount of gravity exerted on an object

SI Units

Gravity ??????????

Weight (do not put on table)

SI Units

• The SI unit for weight is the Newton (N).

**Gravity is a force that

attracts all objects to each other. Bigger

objects will attract smaller objects.

Weight

In the moon: your weight would change but your mass is the same

• There is very little gravity on the moon, that is why we have very little weight on the moon and

that is why we

float on the Moon.

Weight

• On the Moon, the mass of your body ( the amount of matter) is the same as it is on earth

• Your mass is the same everywhere you go.

Spring Scale to measure weight in

Newton

Temperature

• The physical property of temperature is related to how hot or cold an object is.

SI Units

• To measure temperature we use thermometers.

• Temperature is measured in SI with the Kelvin (K) scale or Celsius ( also called Centigrade). The most common is Celsius.

Temperature Scales

• The Fahrenheit and Celsius scales are two common scales used on thermometers and in classroom laboratories.

SI Units

2

Conversion factors

• Examples: To convert from Celsius to

Fahrenheit and vice-versa

F = (C X 1.8) + 32

C = (F – 32) X 0.55

Time

• Time is the interval between two events.

2

• The SI unit of time is the second (s).

• Time also is measured in hours or minutes .