Newton’s Laws of Motion
Speed: Distance/Time = v
•
Average speed
•
Total distance divided by total time
•
X initial might not be the real starting point
o
T2 might be better
o
Be flexible with subscript
•
V = Delta X/ Delta T
o
Xf – Xi/ TfTi
Acceleration
Delta V/Delta t
•
Average = “between”
•
Instantaneous = “at”
•
Normalizing the denominator to units time/volume/ect. (the
denominator is set to 1)
•
Seconds squared
o
D/N exist
o
Acceleration
o
.
•
Bar over letters = average
Test on Wednesday morning February 4
Qui
Instantaneous speed
•
Make the interval shorter
We have now studied how to describe the motion of an object.
This is the
field of
kinematics
.
However, we have not talked about why objects move.
This
is
dynamics
, and is the next subject that we shall look at.
In order to study the dynamics of an object, indeed, even to study the
kinematics of an object, we must choose a coordinate system.
Remember that
coordinates are man made systems that we use to help us convert a physical
situation to a mathematical model.
Unfortunately, there are infinitely many
coordinate systems that we could chose.
Is there some way of consistently
choosing a useful one?
The answer is yes, but in order to fully understand why,
we must define an
inertial frame of reference
.
An inertial frame of reference is
one in which
the object that the coordinate frame is attached is at rest or is
moving at a constant velocity
.
Thus, a car speeding up to get on the freeway
is not an inertial reference frame, but once the car is on the freeway and moving
with a constant velocity it is.
Thus, in order to choose the proper coordinate
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 Spring '09
 Knott
 Physics, Acceleration, Force, Mass

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