Lesson 1 -introduction To Physics

(i) Frequency of oscillation – frequency is the quantity and oscillation is the phenomenon (ii) Length of a wooden block – Length is the quantity and the wooden block is an object (iii) Density of water – density is the quantity and the water is the substance

LESSON 1 Understanding Physics The study of the laws that determine the structure of the universe with reference to the matter and energy of which it consists. The study was divided into separated fields; heat , the properties of matter, light, sound ,wave, electricity, magnetism, mechanics, nuclear physics etc. In physics , there is the need to make careful observations, precise and accurate measurements. Understanding natural phenomena and observing everyday objects such as a table, a mirror etc and discuss how they are related to physics concepts has always been a central aim of physics. The roots of all science are firmly based in experiment. Of course , mastering scientific skills applying scientific knowledge must be the important thing to learn physics.

There are two types of the physical quantities, • Base quantities • Derived quantities Base Quantities The physical quantities which are used as the basis for the measurement and can’t be derived from other physical quantities. There are five base quantities as shown in the following table:

Base quantity

Symb ol

Unit name

Unit Abbreviati on

Measur ed by

Length Mass

Physical Quantities Physics is based on measurement. We discover physics by learning how to measure the quantities that are involved in physics and we call its as physical quantities.

Time Temperatu re Current

The meaning of Physical Quantities Physical quantities are quantities that can be measured. Examples of physical quantities are length, mass, time, weight, pressure, current and force. A physical quantity is a property ascribed to phenomena, objects, or subtaces that be quantified. Example are:

Derived Quantities The physical quantities which were derived from base quantities by multiplication operation or devision operation or both There are three examples for derived quantities as shown in the following table.

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Derive d quanti ty Area

Symb ol

In term of the base quantities

Derived unit

Unit Abbreviati on

Velocit y Density

Example 1 State the following derived quantities in terms of the base quantities. (a)Acceleration (Hint: Acceleration = change of velocity ) time (b) Momentum (Hint : Mometum = mass x velocity )

Scalar and Vector quantities A scalar is any quantity with size (magnitude) but without specified direction. Examples of scalar quantities include mass, time, length, temperature, energy, work, speed and pressure. A vector is any quantity with size (magnitude) and specified direction. Examples of vector quantities are displacement, weight, force, velocity, acceleration and momentum.

Solution

Example 2 State the base units for the following derived quantities: (a) Force (Hint : Force = mass x acceleration ) (b) Impulse (Hint : Impulse = change of momentum)

TUTORIAL 1

(c) Work (Hint : Work = force x displacement)

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Which one of the following is not a base quantity?

A C Time

Solution

Length Current

B

Weight D

2 Which one of the following is not a base unit? A C

2

Celsius Kilogram

B

Ampere D Second

3 All derived quantities can be derived from base quantities by

base quantity A

The weight of an astronaut on the Moon’s surface is 10 N. B The velocity of a cyclist rides a bycle is 70 km j-1 C The perimeter of a field is 380 m D The power of a lamp is 60 W.

A addition operation or subtraction operation B addition operation or subtraction operation or both C multiplication operation or devision operation D multiplication operation or devision operation or both 4

B

miligram D mikrogram

Length B Temperature

Time D Mass

A B C

Which of the derived quantities is the combination of a base quantities only? A B C

Length Mass Time

10 Which one of the following apparatus is not be used to measure the density of a metal cube?

Which one of the base quantities is not involve in force? A C

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gram kilogram

Which one of the base quantities is not involve in acceleration? A B C

The S.I. base unit for mass is A C

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9

Ruler Stop watch Triple beam balance

11 Which one of the following derived quantities contains length and time only?

Force Volume Acceleration

A Velocity Momemtum B Force

B D

Pressure

12 Which one of the following is true? Physical Type of S.I. Unit quantity physical quantity A Momemtu Derived Kg m s2 m quantity o B Temperat Base C ure quantitiy C Work Derived kg m 2 quantity s -2 D Area Basie m2 quantitiy 13 The kinetic energy of a moving object is given by E=½mv2

7 Which one of the following pairs of derived quantities is true? A Work and mass B Force and current C Pressure and temperature D Weight and potential difference 8 Which of the following physical quantities is a

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where m = mass and v = velocity. The number of the base quanrtities involve in the kinetic energy ,E is or are A B C

k = constant The units of k are A

1 2 3

s-1

E

14 Which of the following pairs of physical quantities and S.I. units is true? Physical quantitiy

A C

foot

-1

Kilogram Joules per

A C

Kilograms per metre cubed

A B C

2

Weight Force Acceleration

B D

Volume

Work Velocity

B Power Distance

D

Impulse and area Power and pressure Weight and velocity

21 (a) The current flows through a metal conductor is is defined by the equation

D The S.I. units of acceleration is cms- 2 16 A physical quantitiy is given by M=¾ed2 where the unit of e is unit kilogram and the unit of d is metre. The units of M are B D

kg2 s

20 Which one of the following pairs of vector quantities is true?

The S.I. units of charge is A s The S.I. units of volume is cm 3 The S.I. units of velocity is km

A kg 2 m C kg m 2 E kg 2 m

kg- 1 s 2 D kg- 2

19 Which of the followinq quantity is a vector quantity.

15 Which one of the following is true?

j

B

18 Which of the followinq quantity is a scalar quantity.

S.I. unit

A Area squared B Weight C Power minute D Density

A B C

kg s2 C kg s

current =

charge time

Based on the equation, which of the quantities above are

kg - 2 m kg m - 2

(i) base quantities

17 The period of oscillation for an inertial balance is given by T2= km where T = The period of oscillation and the unit is s , m = Mass and the unit is kg

........................................... ............ (ii) derived quantities ........................................... ............

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(b) charge?

What are the S.I.units of

(i) the base quantities …………………………………

................................................. ..............

……….. (ii) the derived quantities. ………………………………… ……….. (iii) the vector quantities ………………………………… ………... (b) The S.I. units of F,m ,M and R

22 The power of a student to run up a stair is given by the equation Power = force X displacement ti me

(c) The S.I. units of G

(a) State the base quantities contain in the equation above. ................................................. ................... (b) State the power in term of base quantities. ................................................. ................... 20 The Newton’s law of universal gravitation state, the gravitational attraction force, F is directly proportional to the product of the mass ,m and M of two bodies and inversely proportional to the square of distance ,R between them. The law is given by the equation F=GmM R2 Based on the equation, (a) give one example of

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