introduction to measurement - junior science
TRANSCRIPT
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Introduction to Measurement
Junior Science
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Lesson Objectives
• Understand the importance of measurement.
• Know the principles behind the SI System (metric system).
• Identify the units for measuring –Length, Mass, Area and volume.
• Be able to convert between the various metric units.
• List the types of measurement errors which can be made when carrying out investigations.
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Why do we Measure?
Measurement gives a base to understand the world around us.
We are "measuring" things to understand them one way or the other.
Measurement is the process of attaching a numeric value to an aspect of a natural phenomenon. For example: Weather (temperature, Pressure, Wind speed, Rain fall).
This enables us to form an opinion or make a comparison against something else we know
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Temperature
Mass
Length
Volume
Time
Area
Things we Measure
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Measurement Systems
• Two Systems of measurement in use today include
– International System of Units (SI), the modern form of the metric system.
– The Imperial or English system.
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Imperial System
• The English system of measurement has been in use for a very long time.
• It involves units such as pounds and ounces for weight, miles, yards, feet and inches for distance, and pints and gallons for volume.
• It’s not a simple or intuitive system.
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Systeme International (SI) System
• During the French Revolution (1789–1799), the French Academy of Sciences was asked to “deduce an invariable standard for all the measures and all the weights”.
• The Academy decided on two founding principles. The system would be:
– based on scientific observation
– a decimal or base 10 system.
• The metric system is simpler with a series of basic units, one for each of distance, mass, and volume, and a series of prefixes to tell you what multiple of the basic unit is being used.
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The Systeme International (S.I) units
• Length (km, m, cm, mm)
• Mass (kg, g, mg)
• Volume (L, ml, cm3)
• Area (m2, cm2)
• Time (s)
• Temperature (oC Celsius, oK Kelvin)
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Length
• Standard unit of measure is the meter (m)
• 1m = 100cm (centimeter)
• 1cm = 10mm (milimeter)
• 1000m = 1 km (kilometre)
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Measuring Length
Length is the straight line distance between two points.
The SI unit for length is the meter (m)
• Measuring instruments include:
–Ruler
–Opisometer
–Vernier Calipers
–Trundle Wheel
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The Opisometer
An opisometer, also called, is an instrument for measuring the lengths of arbitrary small curved lines.
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Trundle Wheel
• Trundle wheel is used for measuring longer lengths accurately
– Measuring out a pitch length
and width or running track.
• The pointer on the wheel helps to measure distances and Incorporates a clicker that can be adjusted from every 10cm and to a metre.
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The Vernier Calipers
• The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately.
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1. The first reading is taken where the zero in the sliding scale meets the fixed scale.2. The second reading is taken where the sliding scale matches the fixed scale exactly.
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1. Can you find the exact reading above?
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ANSWER : 3.7mm
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MassThe mass of an object is the amount of matter in
it.• Standard unit of measure is the
kilogram (kg)
• Mass can be measured using an electronic balance.
• Mass is measured in kilograms (kg) or grams (g).
• 1kg = 1000g
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Area
The area is the amount of surface that covered an object.
• To measure the area of an regular object we multiply the length x width.
• Area is normally measured in units called squared metres (m2) or squared centimetres (cm2).
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Area
• The area of an irregular object can be estimated using graph paper.
• When measuring count the whole squared and any square more that 50%
1cm2
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Solid VolumeThe Volume of an object is the
amount of space it takes up.
For regular shaped objects we can use formula’s to calculate the volume.
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Liquid VolumeThe Volume of an object is the
amount of space it takes up.
• To measure the volume of a liquid we use a measuring cylinder(graduated cylinder).
• Volume can be measured in units called cubic metres (m3)cubic centimetres (cm3), Litres (L) or millilitres (ml).
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Using a Graduated Cylinder
• When reading the volume, the cylinder should be at rest on a bench and your eye should be level with the bottom of the meniscus.
Meniscus50
40
30
20
10
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Measuring Liquid VolumeBurette, Pipette and Droppers
• To transfer a definite volume of liquid to a container we use a Burette or Pipette ordroppers.
Burette Pipette Dropper
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Accuracy and Error
• All experiments are subject to some errors.
• The most common to occur are:
–Parallax errors
–Zero errors
–Reading errors
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Parallax Errors
Occur when the eye is not placed directly
opposite a scale when the reading is take.
31 32
31.431.45 31.5
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Zero Error
This error occurs when the measuring instrument does
not begin with zero.
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Reading Error
This occurs when you are required to guess the
reading from a scale when the
reading lies between the
scales of division.
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Summary• Mass is the quantity of matter in a substance measured in grams or kilograms.
An electronic balance is used to measure the mass of an object.
• Length is measured in metres (m), centimetres (cm) or kilometres (km).
Length can be measured using a metre stick, a vernier callipers (to measure the diameter of an object), or a trundle wheel or opisometer (for curved lengths, e.g. curved roads on a map).
• The area of an object is the amount of surface it has measured in m2, cm2 or km2.
• For a regularly shaped object (like a square or a rectangle), area is equal to the length multiplied by the width.
• Volume is the amount of space an object takes up measured in L, m3, cm3 or km3
• The volume of an object is equal to its length multiplied by its width multiplied by its height .
• A graduated cylinder, burette or pipette will accurately measure volume of liquids.