Physics

Physics

·         Wave Motion	·         Simple Pendulum	·         Simple Harmonic Motion
·         Mechanical Waves	·         Transverse Waves	·         Compressional Waves
·         Ripple Tank	·         Reflection	·         Refraction
·         Diffraction	·         Interference	·         Stationary Waves
·         Sound	·         How Sound Produced	·         Human Ear
·         Loudness	·         Intensity	·         Pitch
·         Quality of Sound	·         Ultrasonics	·         Electric Current
·         Potential Difference & Emf	·         Ohm’s Law	·         Resistance
·         Resistance Thermometer	·         Galvanometer	·         Ammeter
·         Voltmeter	·         Joule’s Law	·         Electric Power
·         DC & AC	·         Fuse	·         Circuit Breaker
·         Earth Wire	·         Magnetic Effect of Electric Current	·         Force on Current Carrying Conductor in Magnetic Field
·         DC Motor	·         Faraday’s Law of Electromagnetic Induction	·         AC Generator
·         Mutual Induction	·         Self Induction	·         Transformer
·         Electronics	·         Analogue & Digital Electronics	·         Conductor
·         Semi Conductor	·         Insulator	·         Doping
·         P & N Type Semiconductors	·         Semiconductor DIOD	·         Forward & Reverse Biased Diod
·         Rectification	·         Transistor	·         Logic Gates
·         Electric Charge	·         Electrostatic Induction	·         Electroscope
·         Coulomb’s Law	·         Electric Field	·         Electric Lines of Forces
·         Electric Potential	·         Capacitance	·         Combination of Capacitors
·         Types of Capacitors	·         Simple Machines	·         Spherical Mirrors and Lenses
·         Linear Magnification	·         Laws of Refraction	·         Total Internal Reflection
·         Minimum Value of Angle of Deviation	·         Optical Fibre	·         Aberrations or Optical Defects
·         Defects of Vision	·          Deposition	·          Projectile

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WAVES

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WAVE MOTION

Wave motion in a medium is due to the generated disturbance which causes the constituents particles to repeat it's to and fro motion about its mean position in equal interval of time and this disturbance is passed over from one end of the medium to the other.

SIMPLE PENDULUM

A pendulum is a weight suspended from a pivot so that it can swing freely. Acceleration of the bob is always directed towards the mean position. Speed of the bob is maximum at mean position while minimum at the extreme positions. 

SIMPLE HARMONIC MOTION

Simple harmonic motion is a kind of vibratory motion in which acceleration of the body is directly proportional to the displacement from equilibrium position and always directed towards the equilibrium position.

Suppose we take an example of pendulum bob moving about its mean position. When the bob is at extreme position, the acceleration of the body is directed towards mean position and is maximum because the displacement from mean position is maximum. But velocity at this point is minimum. On reaching mean position, the displacement from mean position becomes zero and hence acceleration also becomes zero, but the velocity is maximum at this point. Due to inertia body continues its motion towards other end.

Hence about the SHM we can say that

·    Acceleration is always directly proportional to displacement from mean                 position and is directed towards mean position

·   Acceleration is zero at mean position and maximum at extreme positon.

·    Velocity is minimum at extreme position and maximum at mean position.

Mathematically we can write

a  α – x
f/m  α  -x
f/m=-k/m (x) since k/m is a constant
f=-kx   here is k is called spring constant
the ratio of the external force acting on a spring to the increase in its length is called spring constant. its unit is N/m

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MECHANICAL WAVES

The kinds of waves which require a medium for their propagation are called mechanical waves. The particles of medium do not actually travel but they oscillate about their mean position, it’s the energy that transfers from one medium to another. Sound is a mechanical wave.

Further to note that the waves which do not require any medium to travel are called electromagnetic waves

TRANSVERSE WAVES

The waves in which the particles of medium vibrate perpendicular to the direction of propagation of the wave are called transverse waves.

If you anchor one end of a ribbon or string and hold the other end in your hand, you can create transverse waves by moving your hand up-and-down. Notice though, that you can also launch waves by moving your hand side-to-side.

COMPRESSIONAL OR LONGITUDINAL WAVES

They type of waves in which the direction of the vibratory motion of the particles of medium is parallel to the direction of propagation of the wave.

In longitudinal waves the displacement of the medium is parallel to the propagation of the wave. A wave in a "slinky" is a good visualization. Sound waves in air are longitudinal waves

RIPPLE TANK

Ripple tank is a shallow glass tank of water used to demonstrate the basic types of waves. It consists of a rectangular tray with glass bottom and is placed about half meter above the surface of the table. Waves are produced on the surface of water by means of a vibrator. An electring bulb is hung over the tray, which casts the shadow of crest and trough of the waves on a paper or screen.

REFLECTION

Reflection is a change in direction of a wavefront at an interface between two different media so that wavefront returns into the media through which it is originated. When a ray is reflected by a plane mirror, it is important to note that rotating the mirror at an angle θ, rotates the reflected ray at 2θ. For demonstration please click here. 

REFRACTION

Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. Angle of incidence (angle between incident ray and normal) for which angle of refraction (angle between refracted ray and normal) is ninety degree, is called critical angle. If angle of incidence exceeds critical angle, then the refracted ray comes back into the first medium and hence its called total internal reflection.

DIFFRACTION

Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path. Water waves have the ability to travel around corners, around obstacles and through openings. This ability is most obvious for water waves with longer wavelengths

INTERFERENCE

Interference is addition of two or more waves that result into a new wave pattern.

If identical waves pass through a medium in such a way that crest of one wave falls on the crest of other and trough of one on trough of other, then resultant displacement may get double the displacement of individual wave. Such interference is called constructive interference

And if identical waves pass through a medium in such a way that crest of one falls upon the trough of other,  then they cancel the effect of each other and as a result the surface of medium remains undisturbed. Such interference is called destructive interference.

STATIONARY WAVES

When two waves of same frequency moving in opposite direction superimpose we have stationary waves. The amplitude in such waves is different on different sections. The sections where amplitude is zero are called Anti-nodes (denoted by AN in the fig) and the sections where amplitude is maximum are called Nodes( denoted by N in the fig).

wavelength of such waves is twice the distance between two successive nodes or anti-nodes.

SOUND [Click here for MCQs]
Sound is a physical entity, unlike noise which is the perception of sound. Sound is a travelling wave which is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations

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HOW SOUND IS PRODUCED
Sound is produced by vibrating bodies. By vibrating a body, compressions and rarefactions are produced in the air. The molecules of air vibrate in the direction of wave, hence sound is compressional wave.

HUMAN EAR

The human ear consists of three sections: the outer ear, the middle ear, and the inner ear.

The outer ear includes the auricle (pinna), the visible part of the ear that is attached to the side of the head, and the waxy, dirt-trapping auditory canal. The tympanic membrane (eardrum) separates the external ear from the middle ear, an air-filled cavity. Bridging this cavity are three small bones—the malleus (hammer), the incus (anvil), and the stapes (stirrup). The cochlea and semicircular canals make up the inner ear.

LOUDNESS
Loudness of sound is a characteristic of sound by which a loud and a faint sound can be distinguished. Loudness not only depends upon the intensity of sound but also on physical condition of ear. Loudness also depends upon amplitude and area of vibrating body. 
Amplitude: Amplitude of vibrating body is large, the sound produced will be loud while the sound will be low if amplitude of vibrating body is small.
Area: Larger the area of surface of vibrating body, louder is the sound and vice versa.
Distance: greater the distance, fainter would be voice.
INTENSITY

The intensity of sound, at a given distance, depends upon the amplitude of the waves. Sound energy flowing per second through a unit area held perpendicular to the direction of sound waves is called the intensity of sound. Intensity of sound is a physical quantity and does not depend on the condition and sensitiveness of the ear. Sound level is measured in decibels. A scale for measuring intensity level of sound is called decibel scale

PITCH
The characteristic of sound by which a shrill voice can be distinguished from a grave one is called pitch of sound.

QUALITY OF SOUND
The characteristic of sound by which two sounds of same loudness and pitch can be distinguished from each other is called quality of sound.

 


ULTRASONICS
Sounds of frequency greater than 20,000Hz which are inaudible to human ear are called ultrasonics. In medical ultrasonic waves are being used to diagnose and treat different ailment. They are also used to measure depth of ocean and find out cracks in high speed moving bodies
Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. They can detect frequencies as high as 100 kHz, although there is some disagreement on the upper limit.
Dogs can hear sound at higher frequencies than humans can. A dog whistle exploits this by emitting a high frequency sound to call to a dog. Many dog whistles emit sound in the upper audible range of humans, but some, such as the silent whistle, emit ultrasound at a frequency in the range of 18 kHz to 22 kHz

Electricity [Click here for MCQs]

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Electric current:

The rate of flow of electric charge through any cross section is called electric current. Ampere is the SI unit of current.

Potential difference and emf:

Emf is the total amount of energy supplied by the battery or the cell in driving one coulomb of charge from its positive to the negative terminal through the battery.

Ohm's Law:

The value of current I passing through a conductor is directly proportional to the potential difference V applied across its ends, provided the temperature and the physical state of the conductor does not change.
V α I
V=IR

Resistance:

The property of a substance which opposes the flow of current through it is called its resistance. Its unit is ohm Ω

Resistance thermometer:

Resistance thermometers, also called resistance temperature detectors (RTDs), are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers (PRTs)

Galvanometer:

Galvanometer is a sensitive instrument used to detect current in a circuit. It is connected in a circuit in series.

Ammeter:

It is used to measure the current in a circuit. It is made with slight modification in galvanometer by using a shunt resistance in parallel with galvanometer. Ammeter is used in series in a circuit.

Voltmeter:

It is an instrument used to measure potential difference between two points. Galvanometer is converted to voltmeter by connecting a suitable resistance in series with it. Voltmeter is always connected in parallel with the circuit.

Joule's law:

The amount of heat energy generated in a resistance due to flow of electric current is equal to the product of the square of current, resistance and the time interval
W=I²Rt

Electric power:

The amount of energy supplied by current in unit time is known as electric power.
P=W/t

D.C and A.C:

The current which does not change its direction of flow is known as direct current (D.C).
A current which changes its direction of flow again and again is known as alternating current (A.C).

Fuse:

It is a small wire connected in series with the live wire. A specified value of current can safely pass through it. When the current passing through it exceeds this limit, it gets so hot that it melts and circuits break.

Circuit breaker:

It is a safety device which is used in place of fuse. Due to any fault when the current exceeds the safety limit, then the button of the circuit breaker moves upward. Due to which, the circuit breaks and the flow of the current stops in it.

Circuit Breaker

Earth Wire:

It connects electrical equipments directly to the earth. A connection to ground limits the voltage built up between power circuits and the earth, protecting circuit insulation from damage due to excessive voltage. Connections to ground limits the build-up of static electricity when handling flammable products or when repairing electronic devices.

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Magnetic effect of electric current:

A current carrying conductor produces magnetic field around it in the form of concentric circles. The direction of magnetic field can be determined by right hand rule.

Force on a Current Carrying Conductor in a Magnetic Field:

When a current carrying conductor is placed in a magnetic field, a force acts on the conductor. The direction of force can be determined by left hand rule.

According to this rule, stretch the thumb, forefinger and the middle finger of the left hand mutually at right angles to each other. It the forefinger points in the direction of the magnetic field, then middle finger in the direction of current and the thumb would indicate the direction of force acting on the conductor.

D.C motor:

When a current carrying coil is placed in a magnetic field, it experiences a couple due to which the coil begins to rotate. A D.C motor works on this principle. It converts electrical energy into mechanical energy.

Faraday's Law of Electromagnetic Induction:

When magnetic flux through a coil is changing, an emf is induced in it. The value of this induced emf is directly proportional to the rate of change of flux. This is known as Faraday's law of electromagnetic induction.

A.C Generator:

An A.C generator consists of a coil. When this coil is made to rotate in a magnetic field, the magnetic flux through it continuously changes due to which an alternating voltage is induced in it.

Mutual Induction:

If a change of current in a circuit induces a current in another circuit, this phenomenon is knows as mutual induction.

Self Induction:

If the current through a coil or circuit changes and this changes induces an emf in the circuit itself, the phenomenon is knows as self induction.

When the switch is put on (see fig above), the bulb is not flashed as the voltage of battery is insufficient to turn it on. But when the switch is turned off, bubl flashes for a while which shows a higher voltage has been passed. This high voltage is the self induced voltage produced in the coil at the instant when the switch is put off.

Transformer:

Transformer is an electrical device which is used to increase or decrease the value of an alternating voltage.

Electronics [Click here for MCQs]

Electronics:

It’s the branch of applied physics which discusses those principles and ways by means of which we control the flow of the electrons using diodes, transistors and other semi conductor devices in order to meet our various requirements.

Analogue and Digital Electronics:

Those quantities which, increase or decrease continuously with time or remains constant are known as analogue quantities. The branch of electronics which processes such quantities is knows as analogue electronics.
That branch of electronics which processes the data being provided in the form of digits 0,1 is known as digital electronics.

Conductor:

The materials which allow passage of current and heat through them are called conductors.

Semi-conductor:

These are the substances, the ability of which to conduct current at room temperature lies midway between conductors and insulators.

Insulator:

The materials which do not allow the passage of current and heat through them are called insulators

Doping:

Doping is a process of adding pentavalent and trivalent atoms as impurity into semi conductors.

P and N Type Semi-conductors:

When pentavalent impurity is added to a pure semiconductor crystal, it is known as n-type semi conductor. Where as, due to the addition of trivalent impurity, it becomes p-type material.

Semi-conductor Diod:

When the p and n regions of a p-n junction are connected to metallic wire and enclosed in a glass or metallic case in such a way that only the wires connected to n and p regions project outside the case, then such an encapsulated p-n junction is known as diode.

Forward and Reverse Biased Diod:

When p side of diode is connected to positive terminal of battery and n type with negative terminal, then in this state diode is forward biased. In this state diode acts like a conductor.
When p side of a diode is connected to negative terminal of batter and n type with positive terminal, then diode is reverse biased. In this state diode acts like an insulator.

Rectification:

The process of converting alternating current into direct current is called rectification.

Transistor:

In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much larger than the controlling (input) power, the transistor provides amplification of a signal.

Logic gates:

Logic gates process signals either true or false. A logic gateperforms a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits.Most common forms of logic gates are NOT Gate,AND Gate,NOR Gate

AND Gate: 

A simple AND gate consists of two input and one output. Its output is maximum when both the input are maximum, and output is minimum when any of the input is minimum. It symbol and truth table is show in the image.

Electrostatics

Electric charge: Electric charges are of two types: positive and negative. Like charges repel each other while opposite charges attract each other. Electrostatic induction: If in the presence of a charged body, an insulated conductor has like charges at one end and unlike charges at the other end then this is called electrostatic induction. Electroscope: It is an instrument used for detecting and testing the nature of charge on a body. Coulomb's law: The force of attraction or repulsion between two charged bodies is directly proportional to the product of the quantity of charges on them and inversely proportional to the square of the distance between them. This is called coulomb's law. Let quantity of charges on two points charges be q1 and q2, and distance between them is "r", the according to coulomb's law the force F would be F  α q1q2 And F  α  (1/r2) Combining these two equations F  α [q1q2/r2] Or F = K [q1q2/r2] Here K is Coulomb’s constant and its value is: K= 1/ 4πεo = 9 × 109 Nm2 C-2 Gauss’s Law: Gauss’s Law deals with the electric flux passing through a closed surface due to a charge inside it. It states that when electric flux passes through a closed surface due to charge inside it, then that electric flux is 1/ εo times the total charge enclosed by that closed surface. Mathematically this law can be written as Ø = 1/ εo (q) Where  Ø is electric flux q is total charge enclosed in the closed surface Electric field: The electric field of a charge is a region of space surrounding it, in which a charge can feel its electrostatic effect in the form of a force. Electric lines of forces: The direction of electric intensity in an electric field can also be indicated by drawing lines. These lines are known as electric lines of forces. They are imaginary lines. Electric potential: The potential at any point in the field is defined as the potential energy of a unit positive charge placed at that point which is equal to the amount of work done in bringing a unit positive charge from infinity to that point If W is the amount of work done in bringing a positive test charge +q from infinity to a certain point in the field, the potential V at this point would be V=W/q Capacitance: Capacitance is the ability of a capacitor to store charge. Capacitance of a conductor is equal to the amount of charge which raises the potential of the conductor by one volt. The unit of capacitance is farad. Combinations of capacitors: i)                   Parallel Combination In this method left plates of all capacitors are connected to one point and right one to other point. ii)                 Series Combination  In this combination capacitors are connected plate to plate that is left plate of a capacitor is connected with right plate of other capacitor and so on. Types of capacitors: i)                   Fixed Capacitors If the capacitors are such that its plates are immovable, it is known as a fixed capacitor. Its value does not change. Paper capacitor, mica capacitor etc ii)                 Variable Capacitors If in a parallel plate capacitor some arrangement is made so that the area of the plates facing each other can be charged then it is called variable capacitor. Simple Machines: Simple machines make it easy to do heavy works. All heavy machines are composed to simple machines. Some of simple machines are discussed here Lever: Lever is a simple rod which can move heavy load around a pivot using force. The point around which lever moves is called fulcrum. In the picture shown, a boy is trying to lift up a stool with the help of a simple rod by using a brick as fulcrum. Inclined Plane: Another simple machine that makes work easy is inclined plane. It is a plane surface whose both ends are at different height. It helps to move the things up. Mechanical advantage of inclined plane=l/h where l= Length of inclined plane and H=Height of inclined plane Spherical Mirros and Lenses Spherical mirrors are the portion of a hollow sphere of a reflecting surface. They are of two types: concave mirror and convex mirror. The mirrors whose inner side is reflecting are called concave mirrors whereas the mirrors whose outer curved side is reflecting are called convex mirrors. Linear Magnification: The ratio of the height of the image to that of the object is called as linear magnification or simply magnification and is denoted by letter m. thus Magnification=m=image height/object height Laws of Refraction: i)                   The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plance ii)                 When a ray of light passes from one particular medium to another, the ratio of the since of the angle of incidence(i) to the sine of the angle of refraction(r) is constant and that constant is called refractive index denoted by n. this is also called Snell's law n=sin i/sin r Wavefronts from a point source in the context of Snell's law. The region below the gray line has a higher index of refraction, and proportionally lower speed of light, than the region above it. Total Internal Reflection: The angle of incidence in the denser medium for which corresponding angle of refraction is 90 degrees in the rare medium is called the critical angle. When the value of the angle of incidence becomes greater than the critical angle then the ray does not pass into the second medium that is the ray no longer suffers refraction but all the rays having incidence angle greater than critical angle are totally reflected back in the same medium. Such a reflection is called totally internal reflection Minimum Value of Angle of Deviation: In a prism, when angle of incidence continuously increases the angle of deviation first decreases, reaches a minimum value and then start increasing. The minimum value of angle of deviation is known as the angle of minimum deviation and denoted by Dm n={sin(A+Dm)/2}/sin(A/2) Optical Fiber: The principal of total internal reflection is used in optical fibers. They are made of a highly transparent fine strand of glass or plastic coated with another type of glass whose refractive index is less than the inner tube.  Aberrations or Optical Defects of Lens: i)                   Spherical aberration The parallel rays do not focus at a single point when they refract through a thick lens or lens of large aperture. This defect is called spherical aberration. The rays near the rim of the lens(Marginal Rays) converge more than the rays passing through the axis(Paraxial Rays). This defect can be minimized by covering the lens with a disc of size equal to aperture of lens and having a hole at center. In expensive instruments a combination of lens is also used as shown in the fig above. ii)                 Chromatic aberration The image illuminated by a white light through a convex lens shows colors and is not well defined. This defect is called chromatic abberation. This defect is caused by dispersing of light while passing through the lens. This defect can be minimized by using a combination of lenses called Achromatic Lens Defects of Vision: i)                   Short sightedness That defect of eye due to which one cannot see the distant objects clearly but can see near objects clearly is called short sightedness. In this defect image is formed in front of retina instead at retine. To remove this defect a concave lens of suitable power is used. ii)                 Long sightedness The defect of eye due to which one cannot see the near objects clearly and can see the distant objects clearly is called long sightedness. In this defect light rays passing through the lens do not focus at retina but behind the retine. To remove this defect, a convex lens of suitable power is used. Sputtering: Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It only happens when the kinetic energy of incoming particles is much higher than conventional thermal energies. E Beam Evaporation: E-beam evaporation is a process similar to thermal evaporation i.e. a source material is heated above its boiling/sublimation temperature and evaporated to form a film on the surfaces that is stroke by the evaporated atoms. This evaporation method has just like thermal evaporation a pore ability to cover steps which also makes this method ideal for lift-off processes. A noticeable advantage of e-beam evaporation over thermal evaporation is the possibility to add a larger amount of energy into the source material. This yields a higher density film with an increased adhesion to the substrate. Because the electron beam only heats the source material and not the entire crucible, a lower degree of contamination from the crucible will be present than in the case of thermal evaporation. By using a multiple crucible E-beam gun, several different materials can be deposited without breaking the vacuum. Vacuum Deposition: Vacuum deposition is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub-atmospheric pressure (vacuum). on a solid surface. The layers may be as thin as one atom to millimeters thick (freestanding structures). There may be multiple layers of different materials (e.g.optical coatings). A thickness of less than one micrometer. is generally called a thin film. while a thickness greater than one micrometre is called a coating. The vacuum environment may serve one or more purposes including: ·         reducing the particle density so that the mean free path for collision is long ·         reducing the particle density of undesirable atoms and molecules (contaminants) ·         providing a low pressure plasma environment ·         providing a means for controlling gas and vapor composition ·         providing a means for mass flow control into the processing chamber. Condensing particles may come from a variety of sources including: ·         thermal evaporation, Evaopration (deposition) ·         Sputtering ·         Cathodic arc vaporization ·         Laser ablation ·         decomposition of a chemical vapor precursor, chemical vapor deposition Laser ablation: Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates.. At high laser flux, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave laser beam if the laser intensity is high enough. MBE: Molecular beam epitaxy takes place in high vacuum or ultra-high vacuum (10−8  Pa). The most important aspect of MBE is the deposition rate (typically less than 3000 nm per hour) allows the films to grow epitaxially. These deposition rates require proportionally better vacuum to achieve the same impurity levels as other deposition techniques. The absence of carrier gases as well as the ultra high vacuum environment result in the highest achievable purity of the grown films. Projectile: When a body is thrown upward making a certain angle θ with the horizontal and moves freely under the action of gravitational force, it is called a projectile. The path followed by the projectile is called its trajectory. The trajectory of a projectile is usually parabolic. Such a motion of a body is called projectile motion. The common examples of projectile motion are: ·         A football kicked off by a player ·         A ball thrown by a cricketer ·         A missile fired from a launching pad ·         A thrown base ball ·         Bullet fired from a gun Projectile motion is defined as two dimensional motion under constant acceleration due to gravity. Horizontally Projected Body: Consider the example of a ball thrown horizontally with a certain velocity from a certain height. It is observed that the ball moves forward as well as falls downward until it strikes the ground.