Ch.4 Newton's Laws of Motion & Net Forces

INERTIA MASS FORCE the tendency of an object to resist any change in its motion Inertia is a property of matter and does not depend on the position or location of the object. MASS a quantitative measure of inertia FORCE “a push or pull”

NEWTON’S 1st Law of Motion “Law of Inertia” The velocity of an object remains constant unless acted on by an unbalanced force.

The net force acting on an object is the vector sum of all the forces acting on it. Examples: 8 lb 6 lb 9 lb 8 lb 3 lb 4 lb 8 lb ? 7 lb 7 lb 5 lb 4 lb 4 lb 12 lb If an object is remaining at rest, it is incorrect to assume that there are no forces acting on the object. We can only conclude that the net force on the object is zero.

the condition of an object such that it is not accelerating EQUILIBRIUM the condition of an object such that it is not accelerating Balanced Forces: no net force acting on the object no acceleration Balanced forces are in equilibrium. SF = 0 SFx = 0 and SFy = 0

NEWTON’S 2nd Law of Motion “Law of Acceleration” Acceleration is directly proportional to the net force and inversely proportional to the object’s mass. Fnet = m a

NEWTON’S 3rd Law of Motion “Law of Interaction” Short Version “For every action there is an equal and opposite reaction.” More Scientific Version When one object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude, but opposite in direction.

always, sometimes, never Newton’s Third Law deals with acting on objects. two forces two different Newton’s Third Law pairs of forces always, sometimes, never cancel each other out. The only way for two forces to cancel each other out is for them to be equal and opposite and act on the same object!

How do Newton’s Laws of motion apply to these situations? an object rests in your hand a ball is tossed upward a car windshield hits a bug a person sits on a table a person jumps up from the floor a baseball bat hits a baseball a truck and car hit head-on

Net Forces Forces are VECTORS Net Force is the resultant vector of all forces acting on an object. The SI unit of force is Newton . 1N =1kg·m/s2

Rules for summing vectors are still the same. Examples:

Net Force with more than 1 direction: