We encourage sharing--forward to a friend!
Wikipedia Tour: Fun with Physics (Really!)
Welcome to our Wikipedia Tour: Fun with Physics (Really!). Each day we’ll send you a link to a new article about physics on Wikipedia. The introduction to each day’s article is included in the installment so you can choose to read just the introduction or the full article.
Newton's laws of motion
Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and the motion of the body. They were first compiled by Sir Isaac Newton in his work Philosophiae Naturalis Principia Mathematica, first published on July 5, 1687.  The laws form the basis for classical mechanics and Newton himself used them to explain many results concerning the motion of physical objects. In the third volume of the text, Newton showed that these laws of motion, combined with his law of universal gravitation, explained Kepler's laws of planetary motion.
It is possible to select a set of reference frames, called inertial reference frames, observed from which a particle moves without any change in velocity if no net force acts on it. This law is often simplified into the sentence "A body continues to maintain its state of rest or of uniform motion unless acted upon by an external unbalanced force." This law is known as the law of inertia.
Observed from an inertial reference frame, the net force on a particle is proportional to the time rate of change of its linear momentum: F = d (mv) / dt. Momentum mv is the product of mass and velocity. Force and momentum are vector quantities and the resultant force is found from all the forces present by vector addition. This law is often stated as "F = ma: the net force on an object is equal to the mass of the object multiplied by its acceleration."
Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence "To every action there is an equal and opposite reaction."
In the given interpretation mass, acceleration and (most importantly) force are assumed to be externally defined quantities. This is the most common, but not the only interpretation: one can consider the laws to be a definition of these quantities. Notice that the second law only holds when the observation is made from an inertial reference frame, and since an inertial reference frame is defined by the first law, asking a proof of the first law from the second law is a logical fallacy. At speeds approaching the speed of light the effects of special relativity must be taken into account.
- 1 Newton's three laws
- 2 Importance and range of validity
- 3 Relationship to the conservation laws
- 4 See also
- 5 References and notes
- 6 Further reading
- 7 External links
Click here for the full article.