2.physical quantities 1 K.pptx
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1.2 Physical Quantities and
Their Units
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1. A physical quantity is a quantity that can be measured.
2. Physical quantities are measured in S.I. units.
a. S.I. units means International System of Units.
A. Measurement of Physical Quantities.
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Base quantities.
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1. Prefixes =expressing physical quantities that are either too big or too small.
2. For example, the thickness of a book is measured in centimetres where centi- is the prefix added to metre to express a smaller value.
3. A prefix is added to change the value of the unit.
4. Hence, the value of any physical quantity can be changed to prefix form.
Prefixes used in measurement
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Work examples a. Example 1 Write 45 000 g with the kilo prefix. 45000= 45 X 1000(kilo) 45 kg
Symbol and prefixes
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1. length-straight line- metre rule (mm/cm) - measuring tape curve line- opisometer and metre rule
thread and metre rule
2. temperature- thermometer
Measuring tools
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3. Measure diametera) External diameter-external caliperb) Internal diameter-internal calipers
External diameter=……cmInternal diamerter=…….cmThickness of beaker 1oocm3=
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INTER CALIPERS
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External Diameter
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4. measuring area a) regular object=use mathematical formulae
5cm
2cm
Area = 5cm X 2cm =…………..cm2
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b) irregular object
Estimate area use graph paper
Method:
1) Count the number of complete squares.2) An incomplete square is counted if half
or more of the square is covered. 3) Do not count an incomplete square if less than half of the square is covered.
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b) irregular object= estimate area use graph paper
1cm
1cm
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Area= 27 cm2
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Measuring Volume We often need to measure the volume of
liquids. We use a measuring cylinder, burette or
pipette to measure the volume of a liquid.
We usually measure the volume of a liquid in mililitres (ml) and the volume of a solid in cubic centimetres (cm3).
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Burette
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Pipette
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Measuring cylinder
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Correct eye position is very important when taking readings from the scale of a measuring tool.
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How to read the volume of liquid
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To find the volume of a regular object and irregular object.
In this method, the object is dropped into a measuring cylinder. This will cause the water level in the measuring cylinder to rise. The water level rises because the water in the measuring cylinder has been displaced by the object.
Water Displacement Method
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y mL
x mL
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The volume of water displaced = y-x =50-30 = 20 ml
The volume of the stone = The volume of water displaced.
= (y-x) ml = (y-x) cm3
= 20 ml = 20 cm3
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Measuring Volume of the object
30 ml
45 ml
stone
What is the volume of the stone?
= Water displacement method
Volume of the stone = (45 - 30) = 15 cm3
Suitable for volume of uneven object
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Measuring Volume object less dance than water
30 cm3
45 cm3Object x
load
55.5 cm3
What is the volume of x?
Volume of object x = (55.5 -45) = 10.5cm3
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Volume of stone
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WHAT IS WEIGHT? The weight of an object is the pull of the
Earth (force of gravity) on the object. The S.I unit of weight is Newton (N). The weight of any object depends on the
gravitational force. The weight of an object is obtained using a
spring balance or compression spring balance.
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spring balance
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compression balance
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WHAT IS MASS? The mass of an object is the quantity of
matter in the object. The S.I. unit of mass is kilogram (kg). The mass of an object can be obtained
using a triple beam balance or lever balance.
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Lever balance
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Triple beam balance
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Electronic balance
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EXERCISE 5: CAN U DIFFERENTIATE BETWEEN MASS AND WEIGHT?
MASS WEIGHT
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CAN U DIFFERENTIATE BETWEEN MASS AND WEIGHT?
MASS WEIGHT
It is the amount of matter in an object.
It is the gravitational pull
on an object.
Its value is fixed.Its value varies from place to
place.
Unit: kilogram (kg) Unit: Newton (N)
Measured using beam balance or
lever balance.
Measured using spring balance or weighing balance.
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Importance of standard units in
everyday life
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The use of standard units make it easier for people from different countries to communicate with each other.
The use of a standard unit means a measurement in that unit has the same value anywhere in the world.
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1. Other systems of standard units can be converted to S.I. units and vice versa: a. 1 inch = 2.54 cm b. 1 foot (12 inches) = 30.48 cm c. 1 yard (3 feet) = 0.91 m d. 1 mile = 1.609 km d. 1 mile = 1.609 km e. 1 pound = 0.45 kg f. 1 gallon = 4.5 l