So, forces are synonymous with accelerations.
In other words, a force is a push or a pull on an object that can overcome the
object’s inertia and produce an acceleration.
Now, for a given force, what determines how much acceleration I’m going to get?
It’s the object’s
INERTIA
!
The more inertia (and thus mass) an object has, the more it resists a change
its motion
in its motion.
∑
=
a
m
F
v
v
Newton’s 2
nd
Law
This is Newton’s 2
nd
Law.
In words it says:
The sum of the forces acting on an
object is equal to its mass times its acceleration.
Notice that forces are vectors
.
They require both magnitude and direction to
completely describe them.
Units?
n
ccelerati
ass
⎤
⎡
m
g
⎤
⎡
⋅
m
kg
ewton
[ ][ ]
on
Accelerati
Mass
[ ]
⎥
⎦
⎢
⎣
=
2
s
kg
⎥
⎦
⎢
⎣
=
2
s
[ ]
N
=
Newton
It takes about 1 N of force to push a stamp on an envelope.
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View Full DocumentFrames of reference:
Newton’s First Law (and 2
nd
Law) may be invalid depending on an observer’s
frame of reference
.
Your
frame of reference
(or reference frame) is your perspective
from which you observe a physical system.
In physics we attach a set of coordinate axes to our frame of
reference so that we can measure things like position, velocity, and
acceleration.
For example, let’s say you are standing at rest watching a passenger train go by
you at constant speed.
I’m sitting in my seat on the train with my lap tray down as I enjoy my favorite
cold beverage.
An ice cube from my drink is sitting on the tray in front of me.
As the train goes by you, we both agree that the ice cube is obeying Newton’s
gy
y
,
g
y
g
First Law:
You see the ice cube continue to move in a straight line at constant speed.
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 Fall '08
 SPRUNGER
 Physics, Acceleration, Force, Inertia, General Relativity, Sir Isaac Newton, Ice Cube

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