chapter: measurement
TRANSCRIPT
• 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!!!!!!!!!!!!!!!!!!!
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.
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.
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 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.
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.
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.
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