Measurement Basics in Physics

1©️ 2023 Marshall Cavendish Education Pte Ltd

Chapter 1
Physical
Quantities,
Units and
Measurements

Discover Physics for
GCE ’O’ Level Science and
Normal (A) Level Science

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Activate Prior Knowledge

Launch Quiz 1.1 and 1.2

Launch Quiz 1.1

and 1.2

Let’s play a quiz on your personal learning device to test your prior knowledge
from the past lessons!

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Multiple Choice

Which of the following can be used to measure length?

• Thermometer
• Compass
• Calculator
• Ruler

Multiple Choice

Which of the following has the correct physical quantity and its unit?

• Force - Newtons
• Mass - Kilograms
• Energy - Joules
• Pressure - Pascals

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Chapter 1 Physical Quantities, Units and
Measurements

• 1.1 What is Physics?
• 1.2 What are Physical Quantities?
• 1.3 How Do We Measure Physical Quantities?
• 1.4 What Are Scalars and Vectors?

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1.1 What is Physics?

• Physics is the study of our natural world — from the very large (e.g. the solar system) to the very small (e.g. the atom).

• The Disciplinary Ideas of Physics highlights the overarching ideas of Physics that can be applied to explain real-life problems or phenomena.

• The Disciplinary Ideas are:
− Matter and energy make up the Universe.
− Matter interacts through forces and fields.
− Forces help us understand motion.
− Waves can transfer energy without transferring matter.
− Conservation laws constrain the changes in systems.
− Microscopic models can explain macroscopic phenomena.

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1.1 What is Physics?

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Chapter 1 Physical Quantities, Units and
Measurements

• 1.1 What is Physics?
• 1.2 What are Physical Quantities?
• 1.3 How Do We Measure Physical Quantities?
• 1.4 What Are Scalars and Vectors?

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1.2 What are Physical Quantities?

Learning Outcome(s)

• Show an understanding that physical quantities typically consist of a numerical magnitude and a unit.

• Recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K), amount of substance (mol).

• Use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M), giga (G), tera (T).

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The importance of temperature-taking

• Why is it important to have standardized measurements?

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Fill in the Blanks

What is the temperature of a normal body?

Open Ended

Besides temperature, state another example of a physical quantity.

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Construct
Understanding

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1.2 What are Physical Quantities?

Ingredients for a chocolate
cake

For the cake

• 225 g plain flour

• 350 g caster sugar

• 85 g cocoa powder

• 1½ tsp baking powder

• 1½ tsp bicarbonate soda

• 2 eggs

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• 250 ml milk

• 125 ml vegetable oil

• 2 tsp vanilla extract

• 250 ml boiling water

For the chocolate icing

• 200 g plain chocolate

• 200 ml double cream

Above are the ingredients needed to make a chocolate cake.

• Why is it important to have unit for each ingredient?

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1.2 What are Physical Quantities?

• A physical quantity is a quantity that can be measured.
It consists of a numerical magnitude and a unit

Example 1: A height of 4.5 m

Example 2:The “50” sign refers to a speed limit of 50km/h

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numerical
magnitude

unit

numerical
magnitude

unit

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1.2 What are Physical Quantities?

• In making physical measurements, a system of standardised units called
SI units (International System of Units) is used. SI is short for “Système
International” in French, which means “International System” in English.

Question:
Why is there a need to use SI units?

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1.2 What are Physical Quantities?

• There are seven basic physical quantities, or base quantities.
• The following shows some base quantities and their corresponding SI units.

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Open Ended

What is the 7th base quantity and its SI unit?

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1.2 What are Physical Quantities?

• From the base quantities, derived quantities such as area, volume and speed

can be obtained through equations.

Example:

Speed =

distance

time taken

– Speed is defined as distance travelled per unit time.
– The base quantities are length and time, and the derived quantity

is speed

– Hence, the SI unit for speed is metre per second (m/s).

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1.2 What are Physical Quantities?

Prefixes for SI Units
• It is more convenient to use prefixes to represent physical quantities that are
either very small or very big.

Example 1:

1

1 000 000 of a metre = 0.000 001 m
= 1 × 10^-6 m
= 1 μm (micrometre), where μ represents × 10^-6

Example 2:

1 000 000 000 000 metres = 1 × 10¹² m = 1 Tm,

where T represents the multiple 10¹²

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1.2 What are Physical Quantities?

Prefixes for SI Units

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1.2 What are Physical Quantities?

Standard Form
• Another convenient way of expressing physical quantities is to use the standard form.

• A standard form is a way of writing numbers, in which a number between 1 to 10 is multiplied by an appropriate power of 10.

Example 1: 16 800 = 1.68 × 104

Example 2: 0.01 nm = 1 × 10-11

Example 3: 0.01 m = 1 × 10-8

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Consolidate
Learning

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Let’s Practise 1.1
and 1.2

Check your understanding by trying
out the questions.

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Open Ended

Complete the following statement

"A physical quantity is a..."

Multiple Select

Which of the following are base quantities?

• amount of substance

• area

• electric current

• time

Multiple Choice

Which of the following is NOT a derived quantity?

• Volume
• Temperature
• Speed
• Mass

Multiple Choice

What does SI stand for?

• International System of Units
• International Measurement System
• System of International Units
• Standard International

Multiple Choice

What is the prefix for 10⁹?

• mega
• tera
• kilo
• giga

Multiple Choice

Which of the following is the prefix expression of $$5.5\times10^{-9}$$ s?

• 5.5 ns

• 5.5 μs

• 5.5 ms

• 5.5 Ms

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Enrichment

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The Earliest Timekeeping Device - Sundial

• The oldest known sundial was found in Egypt around 1500 BC.
• Sundials are still being used scientifically by NASA and is currently an important

part of the Mars Rover.

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Questions:
How does a sundial work?
How does a sundial differ
from a clock?