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Isaac Newton The Laws of Motion and Gravity

Isaac Newton  1642 to 1727;  Lived during the last

European plagues, the Baroque period in music, and the beginning of the Age of Reason.  Thinkers who came after saw Newton’s Laws as a description of a Mechanical Universe.

Newton’s First Law of Motion:  An object in constant motion in a straight

line at a constant speed (or at rest) stays in motion in a straight line and constant speed unless acted upon by an external force.  Radical departure from previous ideas of Aristotle who believed objects moved because of their own natural tendencies

Newton’s Second Law:  The acceleration of an object is directly

proportional to, and in the same direction as, the applied force, and is inversely proportional to its mass.  In short, F = ma  Force measured in Newtons, a kg m/s  Weight is a force, not a kilogram.

Newton’s Third Law  The Karma of Physics  For every action there is an equal and

opposite reaction.  The action/reaction pairs occur at a single point. (you feel something you push on with a force equal to your pushing.)

Inertia  A quality, not a dimensional quantity.  Related to mass however.  In Physics, inertia is a resistance to a change

in motion, speed or direction.  Combines all three Laws.

Friction  If the laws of motion or kinematics seem to

be in error, that’s because friction needs to be included. These simple ideas are ideals.  friction is the stickiness between surfaces.  Fluid resistance is like air or water pressure as you move it.  Terminal velocity: the fastest a object can fall in a viscous medium w/o addition force.

Momentum  P = mv  Always conserved! The momentum in a

system before an interaction like a collision is the same as afterwards.  Recoil  Three kinds of collisions: elastic (a clean bounce), inelastic (bending and breaking occurs), and perfectly inelastic (objects stick together).

Gravity  Every object in the universe attracts every

other object with a force directly proportional to the product of the masses and inversely proportional to the square of the distance between their centers.  G is a constant of proportionality