Theory of Relativity Made Simple

Einsteins' Theory of Special Relativity is explained in a simple manner for the interested person.

Every educated person has heard the phrase "Theory of Relativity". However, only few people understand it because it is an advanced concept of physics.

History

Motion and laws of motion were one of the first phenomena studied in detail in modern western science. Their desire was to find the fundamental laws that governed motion so as to express them in terms of precise mathematical formulation.  Galileo Galilee was one of the first to succeed when he proposed his laws of motion, and expressed them in terms of three mathematical expression. These laws and equations are taught at school level even today, and they form an essential framework to understand motion.

Application of the equations of motion gives excellent result for all terrestrial and even celestial moving bodies. However, in 1887 by Albert Michelson and Edward Morley performed a famous experiment on the velocity of light where the equations of motion broke down. The result was totally different from predication. After numerous repetitions it was confirmed that the the experimental results were right and that the equations of motion do not hold in the case of light. This observation perplexed the entire world of physics.

Albert Einstein postulated that the speed of light does not vary with observer, and came up with a mathematical explanation of the the phenomenon in 1905. This explanation was eventually labelled the Special Theory of Relativity, or Relativity in short.

The Special Theory

Since the mathematical derivation given by Einstein gave good result for almost all observations and experiments related to the speed of light and related phenomenon, the theory gained popularity. The application of the theory helps to predict phenomena that take place very near or at the speed of light.

For example, the theory predicts that as the velocity of a moving body approaches the speed of light its mass begins to increase and will become infinite. Since a body of infinite mass needs infinite energy to accelerate it further, and since there is nothing like infinite energy, the theory predicted that moving bodies will never exceed the speed of light.

The mathematical derivations that Einstein also proposed that time should be considered as a dimension of space besides length, breadth, and height. When all of this is put together, another deduction is that mass and energy are two forms of the same entity. This relationship is expressed in terms of the equation shown on the left. E is energy, m is mass and c is the velocity of light. This also implies that if a mass m is completely converted into energy, it would be equal to the mass multiplied by the square of the velocity of light.

Since the velocity of light is 300,000 kilometer per second, one can imagine the huge amount of energy that will be released when one gram of matter is converted into energy. This is the principle behind atomic energy and atom bombs. In atomic energy plants mass is converted into heat energy in a controlled manner and the heat is harnessed to produce electricity. In atom bomb a huge mass is converted into energy within a microscopic period of time and the heat thus released destroyers everything around it.

Conclusion

Some people claim that Einstein proved that everything was relative. On the contrary, what he stated was that the velocity of light is constant. The term Relativity is used for it because of considerations other than relativism of things. The theory has had numerous theoretical and practical consequences, the atomic energy and bomb being only one.

Why is Steel More Elastic than Rubber?

Elasticity is a very interesting word. It came into everyday vocabulary from science, and has acquired a meaning that is totally opposite to the original meaning.

Elasticity According To Physics

Elasticity, as everyone understands, is the property of being stretched and restored. In physics they have discovered that almost all solids have this property. If they are stretched (with a certain limit, of course) they lengthen. On removing the force, they go back to their original shape.

In fact, stretching is not the only thing that can be done. One can stretch, shear, compress, and do many things with force to alter the shape of a solid body. Each time the body returns to the original shape and position after this force is removed. This property of materials to yield to deforming forces, only to come back to the normal shape after the forces are removed is called "elasticity".

Liquids and gases have no permanent shape, and they do not go back to the original shape because they have no shape of their own. However, they can be compressed to decrease their volume. As soon as the forces of compression are removed, they go back to their original volume. Thus even liquids and gases do exhibit what is called volume-elasticity.

The Value Of Elasticity

Physics tries to put everything into measurable quantities. This quantification helps accurate comparison of two things. For example, if the elasticity of different materials is quantified, just a look at those quantities will show which material is more elastic and which one is less.

To quantify elasticity, physics defines elasticity as "resistance to change". The greater the resistance to change, the greater is the elasticity of the material and the faster it comes back to its original shape or configuration when the deforming force is removed. By this definition, steel is more elastic than rubber because steel comes back to its original shape faster than rubber when the deforming forces are removed.

Elasticity In Physics And In Common Life

In common life we label a substance as more elastic if it can be stretched more than others. In physics a substance is labelled more elastic if it offers greater resistance to deformation than other bodies, so that it can be stretched less than others.

The fundamental difference between the definition in physics and definition in common life should always be kept in mind when one speaks of elasticity. Else one is likely to leave his listeners/readers totally confused. Please remember, the more a body can be stretched or deformed without breaking it, the more elastic it is called in common language. Coming to physics, the less a body can be stretched or deformed without breaking it, the more elastic it is considered in physics.

Why Does Black Absorb Heat?

Black as a color absorbs heat because of specific properties of the color and of the light. When light shines on an object, the object’s color either absorbs or reflects the light. A red object, for example, absorbs every color except for red, which reflects back to the eyes. The color of the object depends on the light radiated back to the eyes. If that same red object, like a red apple, were to be illuminated by a light source that had no red wavelength, it would appear almost black, because there would be no wavelength of light to reflect back to the eyes. ‘White, light actually has all of the wavelengths in it, which causes the multitude of colors in life.

Absorption of wavelengths of Light

When white light hits a black object, the object absorbs all of the wavelengths, and none are reflected back, which is why the object appears black in the first place. Now you can think of light as energy in almost all situations: for example, all of the energy that you get comes from the ability of plants to absorb that light energy and store it in sugars. When you eat meat, the animal that you are eating had to get its energy from plants (at the very bottom of the food chain) as well. So when black absorbs the light, it is also absorbing energy. The object then radiates the energy by emitting it at a longer wavelength that is invisible to the eye, but is still energy. It is emitted at the infrared level, which is heat. The key to understanding the transformation of light into heat is that it conserves all energy ‚ one of the laws of thermodynamics, or the study of energy conversion between heat and mechanical work. No heat is lost; it is just transformed into a new form, a new wavelength.

A black car in sunlight absorbs all wavelengths of light eventually heating it up to high temperatures.