Branches of Physics

Physics is the systematic study of natural phenomena that discovers the basic laws of them. Physics is divided into several major topics, namely (1), mechanics, heat, optics, electricity and magnetism, atomic physics and nuclear physics.

Mechanics is the oldest branch of physics that concerns the state of rest or motion of particles and rigid bodies and forces acting on bodies. The subject has three main branches: statics, dynamics and fluid mechanics.

In statics, the forces acting on the body, are so arranged that the body is in equilibrium – it does not move in any way.

Dynamics deals with systems in motion and may be divided into kinetics and kinematics. Kinetics studies the effect of forces in changing the motion of bodies. Kinematics is the science in which the motion of particles or rigid bodies is studied without reference to (2) the forces which produce the motion. Problems in dynamics involve the paths of projectiles (3) (e.g. bullets and rockets), the motion of planets, pendulums and all moving bodies.

Fluid mechanics includes the theory of gases, hydrodynamics (the motion of liquids), and aerodynamics.

The motion of objects and their behaviour are measured in terms of distance, time, velocity, acceleration, mass and force.

Newton’s second law, relating force to acceleration, and his third law, relating action and reaction, form the basis of mechanics.

Sir Isaac Newton defined force and mass and related them to acceleration. Albert Einstein’s theory of relativity superseded (4) Newton’s laws for objects travelling at speeds close to the speed of light.

For atomic and subatomic particles, Newton’s laws were superseded by quantum theory. For everyday phenomena Newton’s laws of motion remain the cornerstone (5) of dynamics, which is the study of motion.

There are several types of motion. First, velocity may be constant. With constant velocity, the average velocity is equal to the velocity at any particular time.

In the second special type of motion, the body moves with an acceleration. Circular motion is another simple type of motion. If an object has constant speed but an acceleration always at right angles to its velocity, it will travel in a circle. Another simple type of motion occurs when a ball is thrown at an angle into the air. The path of the ball is in the shape of a parabola.

The quantity called energy ties together all branches of physics. There are different kinds of energy: gravitational potential energy, electric and magnetic potential energy, kinetic energy and terminal energy, etc. In all transformations from one kind of energy to another the total energy remains the same.

Thus, mechanics is one of the most important branches of physics that concerns the motion of objects and their response (6) to forces.

Machines

Machine is a simple device that affects the force, or effort, which is necessary to do a certain amount of work. Machines make a tough job easier because a person applies less force or applies force in a direction that is easier to manipulate. Machines also increase the speed at which work makes an object travel.

There are four types of simple machines: the lever, the pulley (1), the inclined plane (2), and the wheel and axle. Most mechanical machines, such as automobiles or power tools, are complex machines composed of many parts. Various parts of machines consist of some combinations of the four simple machines. An everyday example of a complex machine is the can opener, which combines a lever (the handle), a wheel and axle (the turning knob), and a wedge (3) (the sharpened cutting disk).

The history of machines dates back thousands of years. The lever was the first simple machine that was utilized by humans. The first levers were branches or logs used to lift heavy objects. In ancient times people used metal or stone wedges when they split wood and rocks. Historians believe the people of ancient Mesopotamia (an early civilization near modern – day Iraq) used wheels as early as 3500 B.C. Chariots in Asia Minor used spoked wheels, which were lighter than solid wheels (4), as early as 2000 B.C.

The Greek inventor Archimedes (287-212 B.C.) developed a screw-type device known as Archimedes’ screw for raising water. Some modern water pumps still use this principle. According to the legend, Archimedes also used a block and tackle (5) to pull ships onto dry land. Machines transform natural energy, such as wind and falling water, into work. Waterwheels and windmills are good examples of simple machines that transform natural energy into reciprocating (6) motion and electricity.

Many everyday objects are combinations of simple machines. They are known as complex machines. An automobile is one of such machines. The engine contains many levers, wheels and axles, and pulleys. The whole engine is held together by bolts, which are a form of inclined plane. The transmission uses gears, which are a form of wheel and axle.

Even devices that do not seem to be mechanical use simple machines. A computer, an electronic device, has a cooling fan. This fan is a complex machine in which the motor shaft turns the fan, which is a form of wheel. The disk drive (7) uses a wheel and axle to turn the disk and a system of levers to position the heads that read and write the data on the disk.

Machines help people make life easier and more comfortable. The production of new generations of machines and equipment increases productivity and promotes (8) technical progress.