M

• MACHINES 

A machine is a device by which we can change a force either in direction or magnitude. They are Slope). Levers, pulleys and ram.

Fig. 1.This was a very popular complex machine.

• M - symbol for mega.           m - mili,         m - mass

A magnetic field is the region in space where magnets and moving charges experience a force.

The SI unit for measuring magnetic field strength is the tesla (T).

This is a measurement of the total magnetic field which passes through a given area

It shows how much magnetic field passes through a given area.

The unit is tesla x meter2.

This is the same as 1 weber. Wb.

Bar magnet

This will have just the appearance of a piece of metal.  We , humans are not equipped with a s sense organ to detect magnetism. (Some birds and a few other animals  seem to be using the magnetic field of the Earth to guide them along their migratory routes)

If a metal bar is a magnet, it will have the following properties.

Fig. The black double arrows show how the metal will sway before coming to rest.

1. If the magnet is placed in a way to freely rotate in a horizontal plane it will come to rest in a north south direction.
2. A magnet will attract pieces of iron.
3. If a magnet is moved inside a metal coil it will generate an electric current. (Refer magnetism and electricity)
4. A magnetic needle will show a deflection in an electric field.
5. Two similar poles of two magnets will repel while the unlike poles will attract. 

         A + h. o x ρ g = A + h.w  x ρ. w      

A cancels off. g also cancels.

Density of water is 1.

Then we get:-   h_o x ρ_o = h.w x 1

Then  .        ρ_o  =  h_w x 1  /  h_o.

• MATTER.

Everything that has mass and volume.

States of matter.

Solid,  Liquid, Gas , Plasma,      Bose-Einstein-condensate.

• MASS

Amount of matter in a body. Measured in grams or kilograms. ( Mass does not change due to changes in gravity)    Weight is measured in newtons and  is equal to the product of mass and acceleration.

Wt = mg.

Matter.

Everything that has mass and volume.

States of matter.

Solid,  Liquid, Gas , Plasma,      Bose-Einstein-condensate.

1.     All bodies either remain at rest or continue at a constant velocity unless an unbalanced force is acting on them.

2.     The acceleration on a body is directly proportional to the magnitude of the force while it is inversely proportional to the mass.

3.     If a body A exerts a force on a body B , then the body B exerts an equal and opposite force on A. (This is generally expressed as “Every Action has an equal and opposite Reaction”)

The unit for the measurement of a force.

This has been obtained by using Newton’s second law.

Acceleration is directly proportional to the force while inversely proportional to its mass

George Ohm showed that the current I in a conductor is directly proportional to the voltage V applied between its ends when the physical conditions are not changed.                          The formula:-  V = IR.

A projectile is an object moving horizontally due to inertia at a regular speed but accelerating down due to force of gravity. ( Although at this level we ignore air resistance there can be reduction of speed due to drag)

  Pqwer is the rate of doing work. Unit:-  Watt.

 Force is a vector quantity. (A quantity that has a direction) Although pressure is derived from a force it does not have a direction. Let us consider pressing a tomato between two surfaces.

As the fruit gets crushed juice will eject in all directions left open. This shows that unlike a force, pressure has definite direction.

1.    Pressure due to solids.

The box here has the opposite sides painted the same colour. It has a mass of 4kg. So whichever way it is placed on a solid surface it will give a force of 400 N.  

The pressure it gives will depend on the surface area touching the ground.

Horizontal position

In this position, (blue side down)

The pressure is measured by the force given to a unit area.    As newtons per square meter.

This has been named as Pascal.

Surface area in contact is =  o.4 X 0.2 m2

                                              = 0.08 m2

The Pressure                      =   Force / Area

                                             =    400 /  0.08 N/m2   or    Pascals.

                                             =     5000 Pa.

The red surface will give the same pressure. Do you know why?

Vertical position

The pressure due to yellow surface will e  =  400 / 0.04 Pa.

                                                                           = 10000 Pa.

2.    Liquid Pressure

In a liquid the pressure has to be determined at different depths.

The pressure on the fish A is not the same as the pressure on the fish B.

Which one gets a higher pressure?

Let’s work it out.

Liquid pressure  =  height (depth) x density x gravity.

On fish A

                             =  0.2 m x   1000 kg/m3 x 10 m,-s2                  

                            =  2000 Pa

On fish B

                            =   0.6 m x   1000 kg/m3 x 10 m,-s2                  

 Gas pressure

a.    Atmosphere pressure           

Atmosphere is the gaseous envelop over the Earth. A direct method as for solids and liquids cannot be used here .  The height of the atmosphere becomes meaningless as there is no definite boundary between outer space and atmosphere. More over as the atmosphere thins out with the height the density of air diminishes gradually.

One of the oldest, yet a very reliable method to determine the atmospheric pressure is to balance it with a column of mercury.  As mercury is a liquid the equation. Pr = hdg can be used to calculate the pressure.

Method:-

 

Take a thin glass tube with one end closed and fill it completely with mercury. Without allowing air bubbles to enter invert this in a cup of mercury as shown. The mercury level in tube will come down while the level in cup will slightly rise. The length of mercury column in tube will have the same pressure as the atmosphere which can be measured by an adjustable scale.
Normal atmospheric pressure is about 760 mm of mercury.

• PLASMA

 

 This is a state of matter when all the molecules are ionised which can happen at a very high temperature

This is a scalar. Measured as the force on a unit area. Pressure due to solids is obtained by dividing the weight by the   area of the base.  

In a liquid it has to be  P = height X density X gravity    

  p = hdg.

• PROTON 

A subatomic particle found in the nucleus of atoms. It has a positive charge and a mass of 1 atomic mass unit. (amu)  (See elementary particles)

• PULLEYS-

      

• Fig. Fixed single pulley

  Fixed Pulley

  
  

• A thread goes round a wheel changing the direction of the pull. If the pulley is frictionless and light the effort will be equal to the Load . 
  

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 R

• R or r - Symbol for resistance.
• RADAR -Radio direction and ranging.

• RADIAN- The arc of a circle equal to its radius. A complete circle has 2π radians. A rad = 360/ 2π degrees.

• RADIATION - Emanation of various rays such as electro magnetic waves or particulate waves such as Alpha and Beta.

• RECTIFIER - A device that can change AC to DC.

• RADIOACTIVITY

Some nuclei of atoms tend to breakdown after some time. Scientists have no way of knowing when a particular isotope (a type of atom) will break down. They have determined what is known as the ‘ half life’  for different isotopes.

The lack of stability of nuclei may be due to massiveness or excess of one type of a particle. An unusual number of neutrons will emit beta particles. Excess of protons emit positrons changing protons to neutrons.  During all changes energy will be released as gamma rays. Very heavy nuclei will give out alpha rays.                                                                           

Radioactivity produces three kinds of rays. Positively charged alpha rays, negatively chargedbeta rays and gamma rays which are similar to X rays. Alpha particles that emanate as alpha rays are really the nuclei of Helium atoms.

Beta rays (particle)  are the negatively charged rays coming out of radioactive substances. They really consist of electrons.

This term Radioactivity was coined by Marie Curie.

• RADIOISOTOPES.

Radioisotopes are radioactive materials formed by the bombardment of alpha,beta and neutrons coming off radioactive matter.

• RAMP.       Click  Inclined plane.

RELATIVE HUMIDITY-Mass of water vapour in a given volume of air upon the mass of water required to saturate it.  This can be obtained by wet and dry bulb thermometers.

RELAY - 

An electrical device by which a smaller current in a circuit can start a circuit carrying a bigger current.

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• RICHTER MAGNITUDE SCALE

Developed by Charles Richter in 1935 in 1934. The Richter magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake. Each number is 10 times more powerful than the previous one

Magnitude	Frequency Per year	Effects	Examples
< 3.4	800 000	Detected only by seismometers
3.5 - 4.2	30 000	Some may notice
4.3 - 4.8	4 800	Felt by all.  Windows rattle
4.9 - 5.4	1400	Objects drop from shelves
5.5 - 6.1	500	Cracks on buildings.	Atomic bomb dropped in Hiroshima.
6.2  6.9	100	Much damage to property	Earthquake in Christ church 2011
7.0 - 7.3	15	Concrete collapse.	Earth quake  in Haiti 2010
7.4 - 7.9	4	Buildings collapse	Meteor crator in Atrizona
> 8.0	5 to 10 years	Objects thrown into air.	eq in shanxi china 1556 killed 830 000 Eruption of Krakatoa in 18

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• REFLECTION
  
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  courtesy-physicsclassroom.com.

Fig. Irregular and regular reflection (specular)

When the path of a traveling particle or a wave is obstructed by a surface it can get deflected and travel in a different direction.  ( A part of the energy can get absorbed too)

Reflection may be specular or diffuse depending on the nature of the surface and the type of wave or particle.

Laws of Specular reflection ( Mirror like)

This kind of reflection occurs in shiny metallic surfaces and glass.                                           1. The angle of incidence is equal to the angle of reflection.   (If the path of a ray or a particle strikes a surface making an angle ‘i’ the path of the reflected ray or particle will also make an angle ‘r’  which would be equal to ‘I’.  )

2.  The incident ray, the normal and the reflected ray are in the same plane

Diffuse reflection.

A ray incident on a rough surface will get split up and scatter in many directions.  This occurs in rough fibrous materials . Marble how ever polished a surface is will never give a silvery surface .

• REFRACTION

When light  enters from one medium to another medium, such as from air  to water the rays bend towards the normal.  This  follows the  law of refraction. Click:- Light-introduction.

S

• s - Symbol for second.
• SCALAR -  Quantities where magnitude is suffice without mentioning a direction.  eg. speed, mass, time, volume etc,.
• SEMI CONDUCTOR- A conductor whose resistance decreases with the rise in temperature.
• SHUNT -A conductor added to bypass a part of the current.
• SHM - Simple Harmonic Motion. eg. Motion in a simple pendulum.
• SNELL'S LAW-  

  This gives the relationship between angles of incidence and refraction for a wave when entering  from one medium to another as from air to water.  

  sine of angle of incidence / Sine of the angle of  refraction = a constant between any two materials.

  This ratio has been termed Refractive index.

• SPECIFIC GRAVITY - The old term for Relative Density.
• SPEED - This is the rate at which displacement is being covered by a moving body. Usually thie is given in meters per second. Speed = Distance / Time. ( Check Velocity too)
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• SPRING CONSTANT -

  Symbol , k, This shows how stiff the spring is. Stiffer springs have higher spring constants. The unit : N/m

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• STATES OF MATTER

Matter may exist as a solid, liquid or a gas depending on the nature of the material, and external factors such as temperature and pressure. But at a very high temperature as in the sun matter exists in a state called plasma state. Here the atoms exist as ions.  

• STANDING WAVE  or STATIONARY WAVE A wave in which each point on the wave has a constant amplitude, ranging from zero at the nodes to a maximum, equal to the amplitude of the wave,at the anti-nodes.This is caused by a wave getting reflected and overlapping the incoming wave.Thee wave does not appear to move. eg. Guitar strings.

• STP - The standard temperature and pressure.
• SURFACE TENSION-  Tension due to the inter molecular attraction of molecules in a liquid. Liquids form a membrane at the surface due to this. Meniscus formation and capillary action are due to this phenomenon.

•  VISIBLE SPECTRUM

Science Museum London 

 

 Fig. A beam of light passing through a prism to produce the spectrum.

Frequency and the Wave length of the visible spectrum.

The two scales are compared here.

 Temperature scales

1. Celcius
2. Kelvin     (Absolute)     

• TACHOMETER -  A device that gives the speed of rotation in an engine. Most cars have this.
• TERMINAL VELOCITY - 
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•  Constant velocity achieved after the acceleration of a body has be couter acted by another force. example A falling parachute jumper.  The force of gravity gets cancelled by the increasing air resistance.

• TESLA-   symbol  T.
• This is the unit for measuring magnetic flux density, sometimes denoted as B. One tesla is equal to one weber m-2,  This was named in honour of Nikola Tesla .

• THERMIONIC EMISSION = Discharge of electrons from heated materials, used in Cathode ray tubes and TV tubes.

• THERMISTOR - a resistor that changes its resistance even with a slight change in temperature.

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• TOTAL INTERNAL REFLECTION

• When the angle of incidence is greater  than the  critical  angle the  rays  get completely reflected  .
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• TRANSMUTATION

Changing of one element into another. This is what happens in radioactive decay. This can also be induced by shooting particles into the nucleus of an isotope.

• TRIBOELECTRICITY

This is produced by close contct, as when rubbing two different materials.

For more click Static electricity.

• TSUNAMI

This is a seismic wave in the sea caused due to an earthquake or a volcanic eruption.

Tsunamis in the deep has a very long wavelength, hundreds of kilometres and a short amplitude 30 or 40 metres. On coming to the shore the wave length shorten, speed decrease and the height increase.

Go to Waves for more;

 U 

• ULTRASONICS

The sense of hearing in human beings is confined to the frequency range of 20 to 20,000 Herts. Any sound wave above that frequency is described as ultrasound.  The hearing range of some animals is given here.

Industrial uses.

How Does Ultrasonic Cleaning Work?

Ultrasonic cleaning is a process that uses ultrasound (high frequency sound waves, usually from 25 – 200 kHz), and with an appropriate cleaning fluid – fine, intensive cleaning of an array of products can be achieved quickly and very effectively. That is the basis of our ultrasonic cleaning and why ultrasonics is such a strong cleaning force....Ultrasonics NZ. 62 AUSTIN STREET, ONEKAWA, NAPIER PO BOX 3127, Napier mail center, Napier 4142, New Zealand

Medical Uses

These include Diagnostic and therapeutic uses.

·         Examining pregnant mothers.

·         Diagnosing  liver problems

·         Investigating heart problems Echo test.

·         Breaking down kidney stones and stones elsewhere in the body

A change in flux of one weber per second will induce an electromotive force of one volt (produce an electric potential difference of one volt across two open-circuited terminals).

Amount of work is measured by the product of distance moved and the magnitude of the force.                  

Work (Joules)  =  Displacement (meters) X  Force (Newtons)  

J = m . N

Waves transmit vibrational energy without transferring matter.

One way to categorise them would be as ‘Mechanical waves’ and ‘Electro magnetic’ waves( EMW).

Mechanical waves require a material medium while EMW can pass through a vacuum.

The other way to classify waves would be as ‘Longitudinal waves’ and ‘Transverse waves’.

Properties of a Wave

a.     Wave length:-

The distance between two consecutive particles at the same state of motion.

b.     Frequency:-

Number of oscillations in one second. (Unit Hertz)

c.      Amplitude:-

d.     Maximum displacement of a particle from the zero line.

 

1.     Longitudinal

In this type of transmission the particles vibrate along the line of the wave.

Examples :-  Sound and Seismic waves.

a.     Sound waves

When an object a bell. Drum or a gutter string is knocked it starts to oscillate. These vibrations disturb the particles in the medium (solid, liquid or gas)  This disturbance travels in all directions until the energy is spent.

The human ear is sensitive only to waves having a frequency of 20 to  20,000 Hz . ( Frequency is the no. of oscillations per second.)

 velocity = frequency x wavelength 

 gives the relationship between the terms.

              V = f l

b.     Seismic Waves

These are formed during explosions in the Earth such as Earth quakes and volcanic eruptions. These are low frequency high energy waves which may propagate as Longitudinal or Transverse waves.

Seismologists have divided these as P-Waves (Primary) and S-waves Secondary).  P – waves reach the observatories before the others.

c.      Tsunami

This is a seismic wave occurring in the sea and rush overland creating havoc.

 
2.     Transverse waves

Here the oscillations are perpendicular to the direction of the wave,

Mechanical waves.

When a flag flutters, wind blows over a field of paddy, corn or water                       

  ( Refer :-     Electro Magnetic Waves)