Forces: Newton's Laws of Motion

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14 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Forces: Newton’s Laws of
Motion

Chapters 6 & 7


Any push or pull exerted on an object.


The object is the system


The forces exerted on the system is the environment.


Force


Contact: acts on an object by touching it.


Long
-
Range: exerted without contact. Gravity


Cause of a force is the agent.



Contact vs. Long
-
Range Forces


“An
obect

that is at rest will remain at rest or an
object that is moving will continue to move in a
straight line with constant speed, if and only if the net
force acting on the object is zero”
Sir Isaac Newton


Law of Inertia.


Inertia is the tendency of an object not
to accelerate.


Equilibrium: occurs if the net force on an object is
zero.

Newton’s 1
st

Law of Motion


The object is at rest, or moving at a constant velocity.


Net force is anything that disturbs a state of
equilibrium


Table 6
-
2 pg. 123

Newton’s 1
st

Law of Motion


A force is needed to keep an object moving.


Inertia is a force.


Air does not exert a force


When an object is thrown, the force of the hand that
throws it remains with the object.


Force Misconceptions


If an outside force is applied to an object, the object
will accelerate.


a=
F

net/m


Net force is the vector sum of two or more forces on
an object.


Weightlessness: no contact forces are acting upon an
object.


Newton’s 2
nd

Law of Motion


Friction is an opposing force acting on an object.


Second force acting in the opposite direction of the
applied force on an object.


Static friction: occurs when there is no relative
motion.


Kinetic friction: occurs when there is relative motion.



Friction


Frictionlike

force exerted when an object moves
through a fluid.


Force depends on the speed of the motion. Faster
the motion, the greater the force.


Air Drag


Initially, it has very little velocity and only a small drag
force


Gravity is stronger than the upward drag force, so
there is downward acceleration


As the object’s velocity increases, so does the drag
force.


Drag force will equal force of gravity.


No net force, no acceleration. Velocity becomes
constant.
Terminal Velocity



When dropping an object


Simple harmonic motion: occurs when the force that
restores the object to equilibrium is directly
proportional to the displacement of the object.


Period: time needed to repeat one complete cycle of
motion.


Amplitude: maximum distance that the object moves
from equilibrium



Periodic Motion


Pendulum: demonstrates periodic motion


Mechanical Resonance: increase in amplitude, occurs
when small forces are applied at regular intervals to a
vibrating or oscillating object.



Periodic Motion


“For every action, there is an equal, opposite
reaction”


Interactive forces: two forces that are “equal and
opposite”


F
A on B
=
-
F
A

on

B


Newton’s 3
rd

Law of Motion


Gravitational Force


Magnetic


Strong Nuclear Force


Weak Nuclear Force


Four Fundamental Forces