Chapter 1.1-physical Quantities (student).pdf

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Foundation in Science (Physics I) Topic 1: Physical Quantities 1.1 Unit Quantities 1.2 Scalar and Vectors Prepared by Siti Azwani & Nor Diana

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Learning Outcomes (a)Know the differences between basic and derived quantities (b)Know and be familiar with the S.I prefix (c)Able to solve a conversion of any units given (d)Know the differences between scalar and vector quantities (e)Able to solve any vector addition and subtraction by using geometrical method and analytical method Prepared by Siti Azwani & Nor Diana

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WHAT IS PHYSICS The word ‘physics’ comes from the Greek word which means_________. Physics was conceived as a study of the natural phenomena around us. Each theory in physics involves: A few concept or physical quantities Assumptions in order to obtain a mathematical model Procedures to relate mathematical models to actual measurement from experiments Relationships between various physical concepts Experimental proofs to devise explanations to natural phenomena Prepared by Siti Azwani & Nor Diana

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UNIT AND QUANTITIES o

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Physics is based on quantities known as physical quantities. Physical quantity is ____________________. Example: length, mass and time. A physical quantity is clearly defined with a numerical value and a unit. In this text, we emphasize the system of units known as SI units, which stands for the French phrase ”Le Systeme International d’Unites”

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UNIT AND QUANTITIES Physical quantity can be categorised into 2 types Basic (base) quantity Derived quantity 1)Basic quantities •___________________________________ •_______________________________________________ •Examples: length, time, mass, temperature, electric current, amount of substance and luminous intensity 2) Derived quantities •____________________________________ •_______________________________________________ •Examples: density, area, acceleration Prepared by Siti Azwani & Nor Diana

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UNIT AND QUANTITIES Units  A unit is a scale with which _________________________.  A standard system of units based on the metric system known as the International System or S.I is used where each basic quantity is assigned with a particular basic unit as shown in table below Basic quantity Base unit Symbol Length Mass Time Electric current Thermodynamic temperature Quantity of matter Luminous intensity Base quantities and their SI base units 6 Prepared by Siti Azwani & Nor Diana

UNIT AND QUANTITIES • The term dimension is used to refer to the physical nature of quantity and the type of unit used to specify it. • The dimension of a physical quantity relates the physical quantity to the base quantities Parameter

Dimension

Distance (x)

[L]

Time (t)

[T]

Mass (m)

[M]

Unit

Speed (v)

m/s

Acceleration (a)

m/s2

Force (F)

Kgm/s2

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UNIT AND QUANTITIES Example 1 Determine the dimension and the S.I unit for the following quantities: (a)Velocity (b)Acceleration Answer:

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UNIT AND QUANTITIES Derived Quantity

Derived Unit

Relationship

Area A

m2

length x width

Volume Vol

m3

length x width x height

Density ρ

kg m-3

Velocity v

ms-1

displacement/ time

Acceleration a

ms-2

velocity/ time

mass/ volume

Frequency f

Hz (hertz)

-

Force F

N (newton)

mass x acceleration

Pressure P

Pa (pascal)

force/ area

Energy E

J (joule)

force x length

Power p

W (watt)

energy/ time

Electric charge Q

C (coulomb)

electrical current x time

Voltage V

V (volt)

power/ electrical current

Resistance R

Ω (ohm)

voltage/ electrical current

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UNIT AND QUANTITIES  In the metric system, larger or smaller units for the same physical quantity are related to the fundamental units by multiples of 10 or 1/10  The names of these units are derived by adding a prefix to the unit of the physical quantity  Examples: the prefix “kilo” always means a unit larger by a factor of 1000, thus • 1 kilometer = 1 km = 1000 meters = 103 m • 1 kilogram = 1 kg = 1000 grams = 103 g • 1 kilojoule = 1 kJ = 1000 Joules = 103 J

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UNIT AND QUANTITIES Prefixes Used in S.I Units Prefix

Multiplying Factor

Symbol f p n µ m c k M G T P

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UNIT AND QUANTITIES • Sometimes, it is necessary to convert one system of units to another. This is done using the conversion factors. • Or to carry out a calculation, it is requires to convert measurements using units in different forms to a common form o 1 mile=1609 m =1.609 km , 1 km = 0.621 mile o 1 ft =0.3048 m =30.48 cm o 1 m = 39.37 in

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SI to C.G.S

C.G.S to SI

1km=1000m

1m=10-3 km

1m2 = 104 cm2

1 cm2 = 10-4 m2

UNIT AND QUANTITIES Some Conversion Factor with S.I. Unit Name of Unit angstrom

Symbol Å

Relation to S.I. Unit ≡ 0.1 nm

atmosphere

atm

≡ 101 325 Pa

electron volt

eV

≈ 1.6 × 10−19 J

mile (international)

mi

≡ 1 609.344 m

degree Celsius

°C

K ≡ °C + 273.15

gallon (Imperial) litre atomic mass unit

gal (Imp) L u; AMU

≡ 4.54609×10−3 m3 ≡ 0.001 m3 ≈ 1.66 × 10−27 kg

tonne (mts unit)

t

= 1 000 kg

1 inch

in

= 2.54 cm

standard gravity

g

= 9.806 65 m/s2

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UNIT AND QUANTITIES Example 2: A proton car may attain maximum speed of 200 km/h. Convert the speed into S.I unit Solution:

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UNIT AND QUANTITIES Example 3: Undergraduate of Mahsa rides a motorcycle at 50 km/h. Express this speed in (a)m/s (b) mile per hour Solution:

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UNIT AND QUANTITIES Example 4: 1.Express the following quantities in term of S.I units (a) 4.5 cms-1 (b) 1.45 gcm-3 (c) 0.12 cm-2 (d) 2.15 gmm-3 2.The sides of a rectangle are 5.5 in and 10.5 in. Find the area of rectangle in meter unit [1 in = 2.54 cm]

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UNIT AND QUANTITIES Example 5 a)Find the volume of cubic which have side 12 in in m3 b) Solve the following problems of unit conversion i.30 mm2 = m2 ii.865 km/h = m/s iii.300 g/cm3 = kg/m3 iv.24 mi/h = km/s

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UNIT AND QUANTITIES [Answer : 1. a) 4.5 x 10-2ms-1, b) 1.45 x 10-3 kgm-3,c) 1.2 x 10-3 m-2,d) 2.15 x 106 kgm-3 2. 3.73x 10-2m2]

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THE END OF TOPIC 1.1:

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