Honors Physics Newton’s First and Third Laws of Motion

Force  Definition – Any push or pull on an object.  Two types of Force: –Contact –Field  A Net Force is required to change the motion of a body.  The Net Force is the sum of all individual forces acting on a body.

Newton’s First Law of Motion  Demonstrations.  An body at rest will remain at rest, and a body in motion will continue in motion with constant velocity, unless acted upon by a net external force.  What is an external force?  In the absence of a net external force, nothing changes.

Inertia  The resistance to a change in motion.  A fundamental property of matter.  It is inertia that makes a body follow the First Law.  For that reason, the first law is also known as the Law of Inertia.  Mass is the measurement of a body’s inertia.

Newton’s Third Law of Motion.  When body one exerts a force on body two, body two exerts and equal but oppositely directed force on body one.  Action/Reaction  Newton realized that he could never produce a single force. They always occurred in pairs.  Demonstrations.

Third-Law-Pairs  The pair of forces exist between the same two bodies.  When identifying the pairs, include only those bodies.  Don’t interpret equal forces as equal results.  Why do the forces not cancel? –Consider a car pulling a trailer.

Questions?  Assignment Questions.