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.


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.

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 subtances that be quantified.
Example are:
(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

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
Length
Mass
Time
Temperature
Current


Derived Quantities
The physical quantities which were derived from base quantities by multiplication operation or division operation or both

There are three examples for derived quantities as shown in the following table.

Derived quantity

Area

Velocity

Density

State the base units for the following derived quantities:
(a) Force
(Hint : Force = mass x acceleration )

(b) Impulse
(Hint : Impulse = change of momentum)

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


Solution

(a)




(b)




(c)

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.

Question

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

current = charge
time

Based on the equation, which of the quantities above are

(i) base quantities

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(ii) derived quantities

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(b) What are the S.I.units of charge?

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

(a) State the base quantities contain
in the equation above.

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(b) State the power in term of base quantities.

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