Science universe: Physics articles

      Einstein put forward new ideas regarding the relationship between space, time, mass and energy which have come to be known as the the theory of relativity . See post Einstein’s Achievements ( Part :2 ) . It had long been accepted that matter could not be destroyed. This assumbtion was expressed in the law of conservation of matter , which states that the total quantity of matter in the universe is fixed and cannot be increased or decreased by human agency . Similarly, another law, called the law of conservation of energy , states that the total quantity of energy in the universe is also constant and can be neither created nor destroyed.       Einstein has simplified our picture of the universe by showing that the mass of a body is a measure of the quantity of energy contained in it . We find that, in a nuclear reactor, the sum total of the masses of the atoms produced as a result of fission is slightly less than the m...

          To every action there is an equal and opposite reaction In other words, if two objects interact, then the force exerted by object 1 on object 2 is equal in magnitude and opposite in direction to the force exerted by object 2 on object 1. Thus, an isolated force cannot exist in nature.   This law has already been mentioned with reference to the force with a table exerts on a book placed upon it and also in connection with the weight o a body in an accelerating elevator ( see post : Newton' second law of motion.... ). We shall now discuss another aspect of the law.     When a bullet is fired from a gun equal and opposite forces are exerted on the bullet and the gun during the time the bullet is passing down the barrel.Since,therefore,both bullet and gun are acted upon by equal forces for the same time, they will, in accordance with the second law of motion, acquire equal and opposite momemta. The backward momentu...

Relativistic linear momentum and the Relativistic form of Newton’s laws    First, recall that the law of conservation of linear momentum states that when two isolated objects collide, their combined total momentum remains constant.     Suppose that the collision is described in a reference frame S in which linear momentum is conserved. If we calculate the velocities in a second reference frame S` using the Lorentz velocity transformation equation and the classical definition of linear momentum,P = mu (where u is the velocity of either object), we find that linear momentum is not conserved in S` . However, because the laws of physics are the same in all inertial frames, linear momentum must be conserved in all frames. In view of this condition and assuming that the Lorentz velocity transformation equation is correct, we must modify the definition of linear momentum to satisfy the following conditions: 1.    Linear m...

Length Contraction                The proper length Lp of an object is the length measured by someone at rest relative to the object. The length of an object measured by someone in a reference frame that is moving with respect to the object is always less than the proper length. This effect is known as length contraction .       Consider a spaceship traveling with a speed v from one star to another. There are two observers:    one on the Earth and the other in the spaceship. The observer at rest on the Earth (and also assumed to be at rest with respect to the two stars) measures the distance between the stars to be the proper length Lp . According to this observer, the time it takes the spaceship to complete the voyage is Δt = Lp /v. Because of time dilation, the space traveler measures a smaller time of travel by the spaceship clock:  The space traveler claims to be at r...

Concerning the theory, Einstein wrote : “ The relativity theory arose from necessity, from serious and deep contradictions in the old theory from which there seemed no escape. The strength of the new theory lies in the consistency and simplicity with which it solves all these difficulties .. “ It is essential to recognize that Einstein was working on electromagnetism when he developed the special theory of relativity . He was confident that Maxwell’s equations were correct, and in order to reconcile them with one of his postulates, he was forced into the freaky opinion of assuming that space and time are not absolute. The postulates of the special theory of relativity Einstein based his special theory of relativity on two postulates: a : The principle of relativity: The laws of physics must be the same in all inertial reference frames- an inertial frame of reference is one in which an object is observed to have no acceleration when no forces act on it-. b : The constanc...

The discovery of quantum mechanics (Photon) Photon First, we need to know : 1. Electromagnetic radiation :            The energy of photons, having properties of both particles and waves. The major wavelength bands are, from short to long: cosmic, ultraviolet, visible or “light,” infrared, and radio .    2. Quantum :        The amount of radiant energy in the different orbits of an electron around the nucleus of an atom.       3. Quantum mechanics :         The theory that has been developed from Max Planck’s quantum principle to describe the physics of the very small. The quantum principle basically states that energy only comes in certain indivisible amounts designated as quanta. Any physical interaction in which energy is exchanged can only exchange integral numbers of quanta. Now ,      The visible ligh...

What is the difinition of momentum ? A motortruck requires a larger force to set in motion when it is heavily loaded than when it is empty. Similarly, far more powerful brakes are needed to stop a heavy goods vehicle than a light car moving with the same speed. The heavier vehicle is said to posses a greater quantity of motion or momentum than the lighter one.     The momentum of a body is defined as the product of its mass and its velocity. The unit of momentum in the SI system is, therefore, 1 kilogramme multiplied by 1 metre per second ( unit sympol, kg m / s ).             When two bodies, a heavy one and a light one, are acted upon by the same force for the same time, the lighter body builds up a higher velocity than the heavy one. But the momentum they gain is the same in both cases. This important connection between force and momentum was recognized by Sir Isaac Newton and expressed by him in a second law of...

Einstein’s theory of general relativity :   The interactions of mass (as related to gravitational force) are really the influence of bodies (masses) on the geometry of space and time. Space and time are affected by gravity. This theory is grounded on two main ideas : that the speed of light is a universal constant in all frames of reference and that gravitational fields are equivalent to acceleration for all frames of reference within the space-time continuum.     The first proofs of the general theory of relativity came from astronomy. It explained the previously unknown reason for the variations in the motions of the planets. The theory then was used to predict the bending of starlight as it passed massive bodies, such as the sun, and as it was detected during a total eclipse.    The theory also predicted that electromagnetic radiation in a strong gravitational field would shift the radiation to longer wavelengths. This was demonstrated by ...