Chapter 4-  Newton's laws of motion

1. Newton's laws

      First law- law of inertia ( inertia is the tendency of bodies to resist a change in its state of motion)

      Second law- cause and effect- acceleration proportional to the net force

                          Net F = ma  ( Units  Metric- F in Newton's, m in Kilograms, a in meter/sec²

                                                          British- F in Pounds, m in Slugs, a in feet/sec²)

     Third law-  action-reaction( forces occur in pairs, for every action force, there is an equal 

                        and opposite  reaction force)    

2.  Newton's law of universal gravitation-    F =  G m₁m₂/r²    

          Weight is  gravitational force-a vector, the force depends on the location of the body.

          Mass is a measure of inertia of a body- a scalar, independent of its location

3.  Forces generally encountered-  Weight of a body

                                                     Normal force- perpendicular to the surface-third law force

                                                      Forces due to friction- a contact force that is proportional 

                                                                                          to the Normal force:  f = µN

                                                      Tension force-strings

4. Applications of Newton's laws:

    Free body diagrams- identifying all the forces acting on a body

    (a) Equilibrium- Net forces on the body zero- no acceleration

                            Net F_x = 0

                            Net F_y = 0

    (b) Non-equilibrium-  Net F_x = m a_x

                                      Net F_y = ma_y