Rifle vs. Riffle

Rifle vs. Riffle Rifle vs. Riffle Rifle vs. Riffle By Maeve Maddox A reader has a question about the verbs rifle and riffle in relation to papers: One word I so often see misspelled in books is riffle. Authors will say,  He rifled through the papers in the file. More often than not, they do not use riffled. I even see it in bestsellers. Actually, papers may be either rifled (long i) or riffled (short i). The words possibly share an etymology with an ancestor that had such meanings as scratch, scrape, steal, and rob. In Piers Plowman (c. 1400), Langland has the allegorical character Covetousness say, â€Å"I rose when they were asleep and rifled their sacks.† Rifle can be used transitively or intransitively to mean, â€Å"make a thorough search.† Sometimes the phrasal â€Å"rifle through† is used. Crime writers (and police) often have occasion to use the verb rifle when describing the aftermath of a break-in: I sat in the black leather chair and carefully  rifled  through the junk mail, bills, and personal correspondence. A peace group in Cleveland reports a break-in of their offices. Some items of value were taken including computer disks and stamps, others were ignored and the office was rifled. The intruder rifled drawers and files but nothing appeared to have been taken. He rifled through a desk and found a security card to the building’s front door. Drawers and filing cabinets had been rifled through and left open, but no property was initially noticed to be missing. â€Å"To riffle papers† is another thing altogether. In the context of moving paper, riffle means, â€Å"to ruffle in a slight or rippling manner.† Anyone who has ever sat outside to read a newspaper or conventional book has experienced the mild annoyance of having one’s reading interrupted by a breeze: The  breeze riffled the pages  and he held them down and stared at the  drawings, which seemed to come to life on the page. Things other than paper may be riffled: Cool  breezes riffled  through Letos hair as he descended toward the warmer surface. A late-afternoon  breeze riffled  the water out beyond the  lazy  breakers and hustled some candy wrappers down the wet brown beach. A sudden  gust riffled  palm fronds overhead, but nothing else stirred. Another use of riffle is to describe the movement of flicking through papers or cards in such a way as to release the leaves or cards in rapid succession: As the  cards  are held and  riffled, the back design of the  cards  are observed.   The dealers  hands  riffled  the deck, and the  cards  made a smooth, purring noise. With rifle and riffle- as with so much else- context is all. Want to improve your English in five minutes a day? Get a subscription and start receiving our writing tips and exercises daily! Keep learning! Browse the Misused Words category, check our popular posts, or choose a related post below:Apply to, Apply for, and Apply withPeace of Mind and A Piece of One's Mind25 Idioms About Bread and Dessert

Principles of Newtons Law of Gravity

Principles of Newtons Law of Gravity Newtons law of gravity defines the attractive force between all objects that possess mass. Understanding the law of gravity, one of the fundamental forces of physics, offers profound insights into the way our universe functions. The Proverbial Apple The famous story that Isaac Newton came up with the idea for the law of gravity by having an apple fall on his head is not true, although he did begin thinking about the issue on his mothers farm when he saw an apple fall from a tree. He wondered if the same force at work on the apple was also at work on the moon. If so, why did the apple fall to the Earth and not the moon? Along with his Three Laws of Motion, Newton also outlined his law of gravity in the 1687 book Philosophiae naturalis principia mathematica (Mathematical Principles of Natural Philosophy), which is generally referred to as the Principia. Johannes Kepler (German physicist, 1571-1630) had developed three laws governing the motion of the five then-known planets. He did not have a theoretical model for the principles governing this movement, but rather achieved them through trial and error over the course of his studies. Newtons work, nearly a century later, was to take the laws of motion he had developed and applied them to planetary motion to develop a rigorous mathematical framework for this planetary motion. Gravitational Forces Newton eventually came to the conclusion that, in fact, the apple and the moon were influenced by the same force. He named that force gravitation (or gravity) after the Latin word gravitas which literally translates into heaviness or weight. In the Principia, Newton defined the force of gravity in the following way (translated from the Latin): Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them. Mathematically, this translates into the force equation: FG Gm1m2/r2 In this equation, the quantities are defined as: Fg The force of gravity (typically in newtons)G The gravitational constant, which adds the proper level of proportionality to the equation. The value of G is 6.67259 x 10-11 N * m2 / kg2, although the value will change if other units are being used.m1 m1 The masses of the two particles (typically in kilograms)r The straight-line distance between the two particles (typically in meters) Interpreting the Equation This equation gives us the magnitude of the force, which is an attractive force and therefore always directed toward the other particle. As per Newtons Third Law of Motion, this force is always equal and opposite. Newtons Three Laws of Motion give us the tools to interpret the motion caused by the force and we see that the particle with less mass (which may or may not be the smaller particle, depending upon their densities) will accelerate more than the other particle. This is why light objects fall to the Earth considerably faster than the Earth falls toward them. Still, the force acting on the light object and the Earth is of identical magnitude, even though it doesnt look that way. It is also significant to note that the force is inversely proportional to the square of the distance between the objects. As objects get further apart, the force of gravity drops very quickly. At most distances, only objects with very high masses such as planets, stars, galaxies, and black holes have any significant gravity effects. Center of Gravity In an object composed of many particles, every particle interacts with every particle of the other object. Since we know that forces (including gravity) are vector quantities, we can view these forces as having components in the parallel and perpendicular directions of the two objects. In some objects, such as spheres of uniform density, the perpendicular components of force will cancel each other out, so we can treat the objects as if they were point particles, concerning ourselves with only the net force between them. The center of gravity of an object (which is generally identical to its center of mass) is useful in these situations. We view gravity and perform calculations as if the entire mass of the object were focused at the center of gravity. In simple shapes - spheres, circular disks, rectangular plates, cubes, etc. - this point is at the geometric center of the object. This idealized model of gravitational interaction can be applied in most practical applications, although in some more esoteric situations such as a non-uniform gravitational field, further care may be necessary for the sake of precision. Gravity Index Newtons Law of GravityGravitational FieldsGravitational Potential EnergyGravity, Quantum Physics, General Relativity Introduction to Gravitational Fields Sir Isaac Newtons law of universal gravitation (i.e. the law of gravity) can be restated  into  the form of a  gravitational field, which can prove to be a useful means of looking at the situation. Instead of calculating the forces between two objects every time, we instead say that an object with mass creates a gravitational field around it. The gravitational field is defined as the force of gravity at a given point divided by the mass of an object at that point. Both  g  and  Fg  have arrows above them, denoting their  vector nature. The source mass  M  is now capitalized. The  r  at the end of the rightmost two formulas has a carat (^) above it, which means that it is a  unit vector  in the direction from the source point of the mass  M. Since the vector points away from the source while the force (and field) are directed toward the source, a negative is introduced to make the vectors point in the correct direction. This equation depicts a  vector field  around  M  which is always directed toward it, with a value equal to an objects gravitational acceleration within the field. The units of the gravitational field are m/s2. Gravity Index Newtons Law of GravityGravitational FieldsGravitational Potential EnergyGravity, Quantum Physics, General Relativity When an object moves in a gravitational field,  work  must be done to get it from one place to another (starting point 1 to  endpoint  2). Using calculus, we take the integral of the force from the starting position to the end position. Since the gravitational constants and the masses remain constant, the integral turns out to be just the integral of 1 /  r2  multiplied by the constants. We define the gravitational potential energy,  U, such that  W  Ã‚  U1  -  U2. This yields the equation to the right, for the Earth (with mass  mE. In some other gravitational field,  mE  would be replaced with the appropriate mass, of course. Gravitational Potential Energy on Earth On the Earth, since we know the quantities involved, the gravitational potential energy  U  can be reduced to an equation in terms of the mass  m  of an object, the acceleration of gravity (g   9.8 m/s), and the distance  y  above the coordinate origin (generally the ground in a gravity problem). This simplified  equation  yields  gravitational potential energy  of: U  Ã‚  mgy There are some other details of applying  gravity on the Earth, but this is the relevant fact with regards to gravitational potential energy. Notice that if  r  gets bigger (an object goes higher), the gravitational potential energy increases (or becomes less negative). If the object moves lower, it gets closer to the Earth, so the gravitational potential energy decreases (becomes more negative). At an infinite difference, the gravitational potential energy goes to zero. In general, we really only care about the  difference  in the potential energy when an object moves in the gravitational field, so this negative value isnt a concern. This formula is applied in energy calculations within a gravitational field.  As a form of energy, gravitational potential energy is subject to  the law of conservation of energy. Gravity Index: Newtons Law of GravityGravitational FieldsGravitational Potential EnergyGravity, Quantum Physics, General Relativity Gravity   General Relativity When Newton presented his theory of gravity, he had no mechanism for how the force worked. Objects drew each other across giant gulfs of empty space, which seemed to go against everything that scientists would expect. It would be over two centuries before a theoretical framework would adequately explain  why  Newtons theory actually worked. In his  Theory of General Relativity,  Albert Einstein  explained gravitation as the curvature of spacetime around any mass. Objects with greater mass caused greater curvature, and thus exhibited greater gravitational pull. This has been supported by research that has shown light actually curves around massive objects such as the sun, which would be predicted by the theory since space itself curves at that point and light will follow the simplest path through space. Theres greater detail to the theory, but thats the major point. Quantum Gravity Current efforts in  quantum physics  are attempting to unify all of the  fundamental forces of physics  into one unified force which manifests in different ways. So far, gravity is proving the greatest hurdle to incorporate into the unified theory. Such a  theory of quantum gravity would finally  unify  general relativity with quantum  mechanics into a single, seamless and elegant view that all of  nature  functions under one fundamental type of particle interaction. In the field of  quantum gravity, it is theorized that there exists a  virtual particle  called a  graviton  that mediates the gravitational  force because that is how the other three fundamental forces operate (or one force, since they have been, essentially, unified together already). The graviton has not, however, been experimentally observed. Applications of Gravity This article has addressed the fundamental principles of gravity. Incorporating gravity into kinematics and mechanics calculations is pretty easy, once you understand how to interpret  gravity on the surface of the Earth. Newtons major goal was to explain planetary motion. As mentioned earlier,  Johannes Kepler  had devised three laws of  planetary motion  without the use of Newtons law of gravity. They are, it turns out, fully consistent and one can prove all of Keplers Laws by applying Newtons theory of universal gravitation.