Physics Chapter 4

Chapter Forces Force - any kind of push or pull on an object –Ex. Hammer, wind, gravity, bat Measuring force –Spring scale Force –Vector quantity Magnitude and direction

Chapter 4 Newton’s First Law of Motion Every body continues in its state of rest or uniform speed in a straight line unless acted upon by an nonzero net force. Inertia tendency of a body to maintain its state of rest or uniform motion in a straight line. 1 st Law = Law of Inertia

Chapter Mass mass - quantity of matter mass - measure of inertia of a body weight - force of gravity acting on a body

Chapter Newton’s 2 nd Law of Motion Relation between acceleration and force Newton’s Second Law of Motion The acceleration of an object is directly proportional to the net force acting on it and is inversely proportional to its mass. The direction of the acceleration is in the direction of the net force acting on the object.

Chapter 4 Net force Net force = vector sum of all forces acting on an object  F=ma Force = mass x acceleration Force - vector quantity - magnitude and direction F x =ma x F y =ma y F z =ma z Unit of force = Newton (N)

Chapter 4 Newton One Newton (N) is the force required to impart an acceleration of 1 m/sec 2 to a mass of 1 kg. 1 N = 1 kg m/sec 2 Examples pg. 82 Ex. 4-1 & 4-2

Chapter Newton’s 3 rd Law of Motion Whenever one object exerts a force on a second object, the second exerts an equal and opposite force on the first.“to every action there is an equal and opposite reaction” Push hand on desk, hand distorted Rocket acceleration –gases do not push against ground or air –Rocket exerts strong force on gasses, and expels them, the gasses exert an equal and opposite force on the rocket Walking on ice

Chapter 4 Conceptual Example Conceptual example 4-3 pg.85 F GP force of ground on person F GP = -F PG Conceptual example 4-4 pg.86

Chapter Weight Weight = mass x acceleration due to gravity W=mg W = newtons m = kg g = -9.8 m/sec 2

Chapter 4 Gravity g on moon = 1/6 g on earth force of gravity - acts while objects falling, acts always Normal force - magnitude and opposite direction as weight acts on same object (not 3 rd law force) Example 4-5 and 4-6 pg.88

Chapter Free Body Diagrams