Motion and its Type
1.0Units & Physical Quantities
Why Study Physics ?
Physics plays an important role in all aspects of our lives. What do flying birds, automobiles, rainbows, and cellular phones have in common ? They all involve physics.
Physics is the branch of science that describes the motion and energy of all matter throughout the universe.
● Birds, for example, use the difference in air pressures above and below their wings to keep themselves up into the atmosphere.
● Automobiles use the principles of physics to transfer stored chemical energy in petrol to moving energy in rotating tires.
● The rainbow is formed due to dispersion of white light into its seven constituent colours.
● Finally, cellular phones use electronic components and the principles of electromagnetic waves to transfer energy and information from one cellular phone to another.
■ Physics is often considered to be the most fundamental of all the sciences. In order to study biology, chemistry, or any other natural science, one should have a firm understanding of the principles of physics. For example, biology, the branch of science that studies living organisms, uses the physics principles of fluid movement to understand how the blood flows through the heart, arteries, and veins.
■ Students often wonder, “Why should I study physics ? What is it going to do for me ?” The answer is that physics plays an important role in everyday life and in the careers of many people. Choosing the right bat, golf club can be made easier with a bit of physics knowledge. While on the job, architects, engineers, electricians, medical technicians, surveyors, and others use the principles of physics every day. When understood, physics can help us to solve difficult physical problems and be better decision makers to determine the best design, tool, or process when working on a specific task.
■ A physicist is a person who is an expert in or who studies physics. It is a physicist’s job to seek an understanding of how the physical universe behaves. Albert Einstein, perhaps one of the most famous physicists of all time, once said, “I am like a child, I always ask the simplest questions”. Such theoretical physicists often spend their professional lives researching previous theories and mathematical models to form new theories in physics. Experimental physicists, however, focus on performing experiments to develop and confirm physical theories.
2.0Physical Quantities
Physical quantities are building blocks of physics in terms of which the laws of physics are expressed. These quantities are measurable and represented by a number, followed by a unit. Physical quantities are divided into two types:
● Fundamental quantities : These quantities are those which cannot be defined in terms of any other physical quantity. Those physical quantities which do not depend on any other quantity are called fundamental quantities. These quantities are also called base quantities. Examples : Length, mass, time, electric current etc.
● Derived quantities : These quantities are those whose formulae are based on fundamental quantities. The physical quantities which are derived from fundamental quantities and which depend on them are called derived quantities. Derived quantities are obtained by dividing or multiplying two or more fundamental quantities. Examples : Speed, density, force, work, energy, power, etc.
● Scalar quantities : The physical quantities which are defined by their magnitudes only are called ‘scalar quantities’. Examples : Mass, volume, density, time, distance, pressure, work, energy, power, temperature, electric charge, electric current, etc.
● Vector quantities : The physical quantities which are defined by their magnitude as well as direction are called ‘vector quantities’. Examples : Displacement, velocity, acceleration, force, etc.
Measurement
A measurement is the comparison of the unknown quantity with some standard quantity of the same kind. A measurement consists of two parts : (1) A number (2) A unit
Units
A unit is the smallest quantity in terms of which other quantities can be measured.
● For measuring a physical quantity a definite magnitude of quantity is taken as standard and the name given to this standard is called unit.
Measure of a physical quantity = Numerical value × size of unit = N × U
N × U = constant. That is, N1U1 = N2U2, this means, on increasing the size of the unit, its numerical value decreases and vice-versa.
Units are also divided into two parts
Fundamental units : The units which cannot be derived from any other units are called fundamental units. In other words, the units of fundamental quantities are called fundamental units.
Examples : unit of length is meter, unit of mass is kilogram, unit of time is second, etc.
Derived units : The units which can be derived from the fundamental units are called derived units. In other words, the units of derived quantities are called derived units. Examples : unit of speed and velocity is m/s, unit of density is kg/m3, unit of electric current is ampere etc.
Seven fundamental units of S.I. system
Frequently Asked Questions
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