Heat & Light Energy
Comparing and Contrasting to see which one is better to use.
COMPARE AND CONTRASTING
- The heat energy of a substance is determined by how active its atoms and molecules are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object's molecules and atoms will be less excited and show less movement. When these guys are in the excited state, they take up a lot of space because they're moving around so fast. When the atoms and molecules settle down, or cool down, they take up less space.
The speed of light is about 300,000 km/s. To put that in perspective, when you watch the sun set, it has actually been 10 minutes since that light left the Sun. Light energy is measured with two main sets of units: radiometry measures light power at all wavelengths and photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception. Photometry is useful when measuring light intended for human use. The photometry units are different from most units because they take into account how the human eye responds to light. Based on this, two light sources which produce the same intensity of visible light do not necessarily appear equally bright.
Light exerts a physical pressure on objects in its path. This is explained by the particle nature of light in which photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by the speed of light. The effect of light pressure is negligible for everyday objects. For example, you can lift a coin with laser pointers, but it would take 1 billion of them to do it. Light pressure can cause asteroids to spin faster by working on them like wind pushing a windmill. That is why some scientist are researching solar sails to propel intersteller flight.