## Kepler's laws of planetary motion

In astronomy , Kepler's laws give a description of the **motion** of planets around the Sun . Kepler's laws are: The orbit of every planet is an ellipse with the Sun at one of the two foci . A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.

**wikipedia.org**| 2011/10/28 6:56:53

## Reactionless drive

is generated without any need for any outside force or net momentum exchange to produce linear **motion** . The name comes from Newton's Third Law of **Motion** , usually expressed as: "For every action, there is an equal and opposite reaction". Such a drive would necessarily violate the conservation

**wikipedia.org**| 2011/7/30 8:31:52

## Physics education

physics courses mechanics usually is the first area of physics that is discussed. Newton's laws of **motion** , which describe how massive objects respond to forces, are central to the study of mechanics. Newton arrived at his three laws of **motion** from an extensive study of empirical data including

**wikipedia.org**| 2011/4/30 20:52:27

## Newton's theorem of revolving orbits

needed to multiply the angular speed of a particle by a factor k without affecting its radial **motion** (Figures 1 and 2). Newton applied his theorem to understanding the overall rotation of orbits ( apsidal precession , Figure 3) that is observed for the Moon and planets . The term "radial

**wikipedia.org**| 2011/4/29 7:55:40

## Lagrangian mechanics

frictionless bead traveling in a groove. If one is tracking the bead as a particle, calculation of the **motion** of the bead using Newtonian mechanics would require solving for the time-varying constraint force required to keep the bead in the groove. For the same problem using Lagrangian mechanics

**wikipedia.org**| 2011/5/10 11:29:09

## Centrifugal force

can be analyzed either in terms of the fictitious force in the rotating coordinate system of the **motion** relative to a center, or in terms of the centripetal and reactive centrifugal forces seen from a non-rotating frame of reference ; these different centrifugal forces are not equal in

**wikipedia.org**| 2011/5/23 4:42:09