sciencecapsules

      The force acting on unit area is called pressure.  Some times, we  want to know what is the pressure give by the atmosphere and it is easier to measure.        When we press on the head of the pin , we give force through the pin to its pointed end.  That is, we concentrate the force on very small area and there by increase the pressure.  Hence the pin easily pierces an object.  For the same reason, a knife cuts.      There are machines which produces jet of water with so much pressure that even cut metals.  Pressure does work.  So it is also a source of energy.   

         Plants do photosynthesis using sunlight and yield us vegetables, fruits and grains.  Humans and animals eat this produce and get energy.      Sun's  heat causes rain and wind.  We derive electrical energy using wind mill.  We generate electricity using fast flowing water.        The plants and the animals that were buried deep inside the earth millions of years ago, have turned into coal and oil due to pressure and heat.  They are the best sources of energy even today.       Today we directly derive electrical energy from solar power and it is one of the best renewable energy .  A solar powered plane has already circumvented the earth.        No wonder that our ancestors had worshiped sun as a god. 

      Simple harmonic motion is the another name for oscillation.  Consider oscillating simple pendulum.  Here the energy alternates between potential and kinetic.  Hence the pendulum oscillates until it is damped by air resistance.  Oscillations give rise to many kind of waves in physics. 1. Oscillating water particles give rise to mechanical water waves 2. Vibrating air molecules is the cause of sound waves. 3. A loop of wire oscillates in a magnetic field and produces electric waves(alternating current). 4. Oscillating charged particles emit electromagnetic waves.   etc;

    Imagine a point rotating on a circular path.  Also imagine a normal line drawn from the point and its foot always touching a diameter.  Again imagine radius connecting the point from the center.  As the point rotates ,  the foot of the normal line  will oscillate on the diameter(simple harmonic motion).  And also as the point rotate, the radius connecting the point will be sweeping the angles.  The sine of those angles will make a wavy graph.      Hence rotation, oscillations, and waves are similar motions and can be related.  Remember rotation of a coil in a generator  produces wavy alternating current.    

      Throw a stone in a calm water surface.  The water particles are set in vibration at the point of disturbance.  This particles cause neighboring particles to oscillate.  These particles disturb their neighboring particles.  Thus the disturbance, vibrations or energy is transfered through the surface of water.  We can see circular waves spreading from the point of disturbance.      The wave is energy conducted through the medium using the vibrations of the particles of the medium.  But the particles themselves are never displaced.      All mechanical waves likes sound waves, string waves,tsunami, earthquake moves in this fashion. When a political idea travels through the minds of the people , we call it a wave.

    Imagine a disc rotating about the axis  passing through its centre.  Also assume that the disc is made up of many particles.  You can observe that the particles at the edge are moving very fast.  But the particles near the axis are moving very slow.  In fact, the linear velocity gradually increases , as we move from axis to the edge along the radius.  This fact should be taken into account when we make rotating devices like DVD player, wheels, gears etc.,     When a whole body moves in a straight line, all the particles in the body moves with the very same velocity.  

     Physics says, when a force is applied on an object and it moves to certain distance, work is said to be done.  The capacity for doing work is energy.      A body at a height, can fall down due to gravitational force . So it said to posses 'potential energy'.        A fast moving body can hit another body and do some work.  So it has 'kinetic energy'.      Petrol can burn, produce heat, gases expand,  pushes the piston of an engine and does some work.  Hence petrol has 'chemical energy' (heat energy)      The chemical in the battery reacts and push the electrons from one electrode to another making electric current.  So the battery stores 'chemical energy'.      When light falls on certain materials, it ejects electrons.  So even light has energy      

      Earth attracts each and every body with gravitational force.  A freely falling body is continuously accelerated because gravitational force is continuously acting on it.  Gravitational force on a falling body is proportional to the body's mass.  Hence feather and boulder falls with same acceleration according to this formula g = f/m.  Hence  g = 9.8 m/s^2  is a constant near the surface of the earth.     The  g depends on the mass of  the celestial body.  g  is small on the moon.  So jumping will be very easy on the moon.  g is greater on Jupiter.  So even walking will be difficult on it 

          Force is not at all required for maintaining  the motion of  a body.  Force is only required to kick-start the movement, change the direction or accelerate the body.  But we are under wrong impression, because in our environment, air resistance and friction slows down the object.  To overcome these resistances, we are forced to apply force frequently.         Railway system use this principle for transportation(friction is greatly reduced in the tracks).  Planets and satellites go round for a long time without the use of force.  Scientists are trying to make a superconductor in which the resistance is totally eliminated and the current (electrons) will flow for ever .