How has our understanding of Gravity changed over the years?
Greek philosopher Looked for the causes of motion Classified motion as natural or violent An example of a natural motion - rocks falling to the ground because the ground is the natural place for a rock to be An example of a violent motion – an arrow shot through space is not natural because the natural motion would be to fall straight to the ground Aristotelian explanation of gravity, 1st Law of Motion, was that objects fall to the Earth because they are trying to reach their natural place in contact with the Earth with a constant speed depending on the nature of the object (heavy or light) Heavier objects fall faster than lighter objects Aristotle (384-322 b.c.)
Proposed a whole new way of looking at the problem of motion Concentrated on describing mathematically what happened rather than speculate why Galileo believed that objects move downward because the gravity disturbs their motion Experimented and shared results as evidence for his beliefs Galileo believed that in the absence of air resistance all objects will fall to the Earth with a constant acceleration Galileo galilei (1564-1642)
Born the year thatGalileo died Took his work and expounded upon it Law of Universal Gravitation - states that every object in the universe attracts every other object with a force which is directly proportional to their masses and inversely proportional to the distance between them Three Laws of Motion 1st Law: Law of inertia – objects at rest stay at rest and objects in motion stay in motion unless acted on by an outside force 2nd Law: F = ma 3rd Law: For every action force there is an equal and opposite reaction force Newton explained that the motion of objects on Earth and celestial bodies were governed by the same set of laws Sir Isaac newton (1642- 1726)
This is a great example of this difference between a law and a theory There is a major misconception that theories will one day become laws This is not true Theories and laws are different A law is a description of a pattern found in nature. It is often a mathematical equation that is found to fit the pattern. A theory is an explanation of a pattern. It is the answer to why there is a pattern. this is a greatexample
Newton described the relationship between mass, distance, and gravitational attraction. This relationship could be written with the equation F = G(m1m2/R2) where G is the universal gravitational constant, m1 is the mass of one body, m2 is the mass of the second body, and R2 is the distance between them squared This is known as Newton’s Law of Universal Gravitation What newton knew…
There was not in Newton’s time, nor is there now, any well accepted explanation of why there is gravity and why this law holds true. There is no theory of gravity. Newton himself understood the difference between law and theory, “…I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypothesis … it is enough that gravity does really exist, and act according to the laws which we have explained…” (Newton, 1720/1946, p. 547). And what he didn’t know
Do Newton’s laws still hold? Has anything been discovered since 1727? Well actually, there has been Newton’s Laws of Motion give us a complete description of the behavior of moving objects at low speeds But, Einstein describes the motion of particles moving at close to the speed of light in his special theory of relativity How is most of our motion described? We move pretty slowly compared to the speed of light, so Newton’s laws describe the motions that we see and deal with every day However if you become an atomic physicist, you may work with a particle accelerator that does not follow Newton’s laws So is that it?
Laws of Motion - examples, body, process, Earth, law, energy, reaction, air, change, surface, History, Newtons three laws. (n.d.). Science Clarified. Retrieved October 24, 2010, from http://www.scienceclarified.com/Io-Ma/Laws-of-Motion.html Newton, I. (1946). Sir Isaac Newton’s mathematical principles of natural philosophy and his system of the world, A Motte, trans; revised and appendix supplied by F. Cajori, Berkeley, CA, University of California Press, (Original work published 1720). Theory: Special Relativity (SLAC VVC). (2009, June 15). SLAC Public Website Server. Retrieved October 24, 2010, from http://www2.slac.stanford.edu/vvc/theory/relativity.html References