Physics and Newton's Laws of Motion

 Kinematics = the study of the description of motion

 Dynamics = the study of forces and the motion resulting from those forces

 scalar quantities = consist only of a magnitude

vector quantities = consist of both magnitude and direction.  The magnitude has a number and a unit.

 Inertia = the tendency of an object to preserve its motion (this is a property of all matter)

Newton's First Law of Motion

 In the absence of a net force acting on it, an object at rest will remain at rest and an object in uniform motion will continue at a constant velocity in a straight line.

 An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

 An object tends to resist any change in its motion (it keeps on doing what it's doing) unless acted upon by a net or  unbalanced force.

 Example:  coffee in a cup while in a car, seat belts in a car

 If an object is at rest the sum of all external forces is zero and its acceleration is zero.

   SF = 0                         a = 0

Newton's Second Law of Motion

 Newton's second law pertains to the behavior of objects for which all existing forces are not balanced.

 According to Newton, an object will only accelerate if there is a net or unbalanced force acting on it.

 The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

 The net force acting upon an object is equal to the product of the mass and the acceleration; the direction of the force is the same as that of the object's acceleration.

 The acceleration of a body is proportional to the force acting (applied) on it an inversely proportional to the mass of the object.

 Remember:  when the net force on an object is zero, its acceleration is zero.

 a = ΣF                  ΣF = m * a                          m = ΣF
         m                                                                          a

 Newton's Third Law of Motion

 A force is any influence that can produce a change in velocity of an object.  It results from interaction between objects.

 When an object exerts a force on another object, the second object exerts on the first a force of the same magnitude but in the opposite direction.

For every action (force) there is an equal and opposite reaction and they are on different objects.  Forces always come in pairs--equal and opposite action-reaction force pairs.

 action force--the force that one object exerts on another

reaction force--the equal but opposite force that the second exerts on the first

 examples:  push against a wall, throw a ball, fire a rifle (recoil), apple falls to earth due to gravitational pull of earth (there is an equal pull by apple on the earth but it cannot be detected because the earth is so massive), walking.

 F_AB = -F_AB