Dark Energy

Astronomers studying the cosmic microwave background (CMB) have found new direct evidence for dark energy, the mysterious substance that appears to be accelerating the expansion of the universe. Their findings could also help map the structure of dark matter on the universe's largest length scales. The CMB is the faint afterglow of the universe's birth in the Big Bang. About 400,000 years after its creation, the universe had cooled sufficiently to allow electrons to bind to atomic nuclei. This "recombination" set the CMB radiation free from the dense fog of plasma that was containing it. Space telescopes such as WMAP and Planck have charted the CMB and found its presence in all parts of the sky, with a temperature of 2.7 K. Measurements also show tiny fluctuations in this temperature on the scale of one part in a million. These fluctuations follow a Gaussian distribution. 


For more information go to http://physicsworld.com/cws/article/news/46572

Picture Courtesy of European Space Agency

Some Laws of Science

Newton's Laws of Motion


First law states that the velocity of an object will stay constant unless acted on by an external force.


Second law states that the force is proportional to the rate of change of momentum.


Third law states that for every action there is a equal and opposite reaction.




Kepler's Laws of Planetary Motion


First law states that the orbit of every planet is an ellipse with the Sun at one of the two focus.


Second law states that a line joining a planet and the Sun sweeps out equal areas during equal intervals of time.


Third law states that the square of the orbital period is directly proportional to the cube of the semi-major axis of its orbit.




Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.




Euler's Laws of Motion


First law states that the linear momentum of a body is equal to the product of the mass of the body and velocity of its center of mass. Internal forces between the particles that make up a body, do not contribute to changing the total momentum of the body.


Second law states that the rate of change of angular momentum about a point is equal to the sum of the external moments about that point.




Archimede's principle states that any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.




Newton's law of cooling states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings.




Gas Laws


Boyle's law states that for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional.


Charles's law states that for a fixed amount of an ideal gas kept at a constant pressure, volume and temperature are directly proportional.


Gay-Lussac's law states that for a fixed amount of an ideal gas kept at a constant volume, pressure and temperature are directly proportional.


Avogadro's law states that the volume occupied by an ideal gas is proportional to the amount of moles present in the container.




Laws of Thermodynamics


Zeroth law states that if system A and system B are in thermal equilibrium with system C, then system A is in thermal equilibrium with system B.


First law states that in a thermodynamic process, the increment in the internal energy of a system is equal to the difference between the increment of heat accumulated by the system and the increment of work done by it.


Second law states that no process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature.


Third law states that the entropy of a perfect crystal approaches zero as temperature approaches absolute zero.

Airplanes Can Make it Rain

Humans can encourage rain or snow by "seeding" clouds by dispersing small particles into the atmosphere. These particles act as nuclei onto which droplets of liquid water inside clouds can freeze, producing ice crystals that, when large enough, fall to Earth in the form of snow or rain. These droplets often exist in a "supercooled" state at temperatures as low as –38 °C and the introduction of particles into clouds raises this minimum temperature. Due to this process which has been noticed in recent years, there is more precipitation around airports. 


For more information go to http://physicsworld.com/cws/article/news/46388

Picture Courtesy of Eric Zrubek and Michael Carmody