Laws of Newton

Classical mechanics is based on Isaac Newton's three laws of motion, which constituted the basis of the whole of classical physics. In 1687, Newton first published the three laws in his Principia, whose full title is The Mathematical Principles of Natural Philosophy.Until the beginning of the 20th century, classical physics was considered correct, and, in fact, serves even to this day to explain familiar everyday activities.

The laws of motion - Newton's dynamics:

The first law - the law of momentum.

This law posits that every body remains at rest or moves with constat velocity in a straight line, unless it is compelled to change that state by a force acting upon it.
This law posits that every body remains at rest or moves with constat velocity in a straight line, unless it is compelled to change that state by a force acting upon it.
This law does not require that no force be exerted on the body, but only that the sum of the forces exerted should be zero.
For example: An ice skater moving at a speed of 5 meters per second will continue to move at this speed so long as nothing stops him (when he reaches the wall at the end of the rink he is sure to come to a stop). In this example the skater is subjected to two forces which cancel each other out: The force of gravity (exerted on the skater's mass) and the "normal force" exerted on the skater by the skating surface. These forces cancel each other so their sum is zero.

The second law - the law of acceleration.

This law posits that the acceleration of an object is directly proportional to the force causing it. The relationship between the acceleration and the force is determined by the mass (the amount of material) of the object. The greater the sum of forces acting on the body, the greater its acceleration.

Galileo's law of fall is a specific example of Newton's second law of motion which deals with constant forces. In this case (of a constant force), the distance which the object traverses is directly proportional to the square of time.

The third law - the law of action and reaction.

The action of a force exerted by one body on a second body produces a reaction that is equal and opposite in direction to the action.
This law means that if I exert my weight on the floor, the floor exerts an equal force on me. A more surprising result of this law is that if I exert force on a carriage which begins to move, it exerts an opposing force on me.

Physicists Predicts Novel Phenomena in Exotic Material

Physicists Predicts Novel Phenomena in Exotic Material

A SLAC-led research team manipulated a beam of electrons (from top left to bottom right) with conventional laser light (red) in a way that could produce purer, more stable pulses in X-ray lasers.

Credit: SLAC National Accelerator Laboratory

Researchers from the Department of Energy's SLAC National Accelerator Laboratory and Shanghai Jiao Tong University in China have developed a method that could open up new scientific avenues by making the light from powerful X-ray lasers much more stable and its color more pure.

The idea behind the technique is to "seed" X-ray lasers with regular lasers, whose light already has these qualities.

"X-ray lasers have very bright, very short pulses that are useful for all sorts of groundbreaking studies," says SLAC accelerator physicist Erik Hemsing, the lead author of a study published today in Nature Photonics. "But the process that generates those X-rays also makes them 'noisy' -- each pulse is a little bit different and contains a range of X-ray wavelengths, or colors -- so they can't be used for certain experiments. We've now demonstrated a technique that will allow the use of conventional lasers to make stable, single-wavelength X-rays that are exactly the same from one pulse to the next."

The method, called echo-enabled harmonic generation (EEHG), could enable new types of experiments, such as more detailed studies of electron motions in molecules.

"We need better control over X-ray pulses for such experiments," says Jerome Hastings, a researcher at SLAC's Linac Coherent Light Source (LCLS) X-ray laser, who was not involved in the study. "The new study demonstrates that EEHG is a very promising method to get us there, and it could become a driver for science that can't be done today." LCLS is a DOE Office of Science User Facility.

Relativity

Gravitational waves predicted by Albert Einstein's general theory of relativity have been detected directly at last. Einstein was right. You can see our full discovery story here; a video on the find here; and our complete coverage of the historic scientific discovery here.

In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.

Einstein then spent 10 years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.

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The tug of gravity

Two objects exert a force of attraction on one another known as "gravity." Sir Isaac Newton quantified the gravity between two objects when he formulated his three laws of motion. The force tugging between two bodies depends on how massive each one is and how far apart the two lie. Even as the center of the Earth is pulling you toward it (keeping you firmly lodged on the ground), your center of mass is pulling back at the Earth. But the more massive body barely feels the tug from you, while with your much smaller mass you find yourself firmly rooted thanks to that same force. Yet Newton's laws assume that gravity is an innate force of an object that can act over a distance.

Albert Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.

As he worked out the equations for his general theory of relativity, Einstein realized that massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space

- See more at: http://www.space.com/17661-theory-general-relativity.html#sthash.0RTQadCg.dpuf