Physics 121 – Study Guide for Final Exam
The purpose of this document is to give you a better idea of what you do and do not need to
know for the final exam.
I’ll try to make it all clear, but if you have any questions, please ask me
during office hours or else send me an email.
Part 1:
Fundamentals of motion and forces
We started out talking about some very basic things: modeling an object as a point particle with a
definite position, setting up a coordinate system to describe that position quantitatively and
representing how the position changes over time with either a ―motion diagram‖ (a bunch of dots
representing the position at a sequence of points in time) or a graph of position versus time, i.e.
x(t).
The graphical approach helped us to interpret velocity as the slope of the x(t) graph, and we
went on to talk about acceleration and its similar relationship to velocity.
You should know the
distinction between average velocity (or average acceleration), averaged over a time interval, and
instantaneous velocity (or instantaneous acceleration) at some point in time.
In general these are
vectors, but in the first part of the course we focused on onedimensional situations so they could
be represented by signed scalar values.
You should be very comfortable by now with the relationships among position, velocity and
acceleration, and how to take a graph of one and sketch from it a graph of the other(s) based on
the appropriate slope or areaunderthegraph relationship.
You should also be able to tell from a
graph whether each of these quantities is positive, negative or zero at a given point in time.
Moving on from graphical relationships, you should be able to solve problems using the special
case of constant acceleration and the even more special case of constant velocity (i.e. zero
acceleration) using the definitions of these quantities plus a couple handy kinematics formulas.
Newton’s laws of motion provide the powerful foundation for understanding
why
things move—
or do not move.
You should know the three laws and how each one applies to a given physical
situation.
In particular, a given object will accelerate if and only if there is a nonzero net force,
where the net force is the sum (as signed scalars in one dimension, or as vectors in general) of all
of the forces acting
on that object
.
Note that an object moving with constant velocity (or else at
rest) must have zero net force acting on it, i.e. it is at equilibrium.
We talked about several types of forces which you should be comfortable working with:
Force of gravity (i.e., weight) – always present and with magnitude
mg
(downward!) near
the surface of the Earth; has a different magnitude in orbit or near other planets, etc.
Spring force – know how the force it applies (at both ends!) depends on the extension or
compression of the spring and on a spring constant
k
(Hooke’s law).
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 Fall '10
 Shawhan
 Physics, Energy, Force

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