4.1 Motion and Forces NOTES
AP Physics
Describing motion (what we have done so far) is called _________________.
Explaining why motion occurs is called _________________ (which we will
now begin to do).
The combination of kinematics and dynamics is called ________________.
What causes motion?
Galileo’s thought with an object on a track:
If the track completely flattens out, the object should go __________________.
Newton’s First Law An object has no _________________ acting on it. If it is
at ____________ it will remain at _____________. If it is
_______________, it will continue to move in a straight
_______________ at a constant ______________.
Newton’s First Law is also sometimes called the Law of ________________.
Inertia refers to the tendency for something to resist a ___________ in motion.
Remember that dynamics concerns what causes motion. From Newton’s First
Law, then, we can say that ____________ either causes ____________ (for
something initially at rest) or will cause a _____________ in motion (for
something that is already moving).
Since a force is the ultimate cause of motion or change in motion, it is
important to understand what a force is.
A force:
is a _________ or a _________ (it is an ___________).
__________ on an __________ (it is __________ to something).
requires an ______________ (something that pushes or pulls).
is a ____________ (it has both ___________ and ___________).
can be a ____________ force ( __________ the object it is applied to).
or it can be ____________________ (does not touch the object it is
applied to). Examples of long-range forces are ____________
and __________________.
is an ____________ between two objects (if you push on a door, the
door pushes back on you).
In drawing a force vector:
Represent the object as a ____________.
Place the ___________ of the force vector
on the particle. (whether it is a push or
pull as vectors can be moved parallel to
themselves and remain the same
vector).
Draw the force vector as an arrow pointing
in the direction the force acts with
length proportional to force size.
Give the vector an appropriate label.
Similar to vectors we have been looking at so far, we can combine force vectors
by adding the vectors. The sum of all forces acting on an object is called the
________________, ________.
Examples of forces acting on a body and determining the net force:
Section 4.2 A Short catalog of Forces
Weight: _____________ pull of the earth on an object is called its weight. An
object’s weight vector always points vertically _______________.
Spring: A spring can either _________ (when ____________) or __________
(when _______________). The way to draw a force vector for a
spring acting on an object is shown below for either pushing or
pulling.
Tension: Force of a string, rope, or wire on an object. The tension force of
always in the direction of the string.
Normal Force: Force exerted by a surface (the ____________) against an
object that is pressing against the surface. The surface exerts a
force normal (perpendicular) to itself.
Friction: Force exerted by a surface that is _______________ to the surface.
two types of friction are:
_____________ friction: Acts as an object slides across a surface. It
always opposes motion.
_____________ friciton: Force that keeps an object in place on a
surface, and prevents motion.
Drag: Force that resists motion through a ______________. It acts opposite to
the direction of motion.
4.3 Identifying Forces
In analyzing the forces acting on a body, it is of course necessary to identify
what all of the forces are. Tactics box 4.2 (page 139) goes through a rather
formal way of identifying the forces acting on a body:
1.) __________ the object you are analyzing the forces on.
2.) ___________ a picture of the situation. (show object and everything
that touches the object).
3.) Draw a ____________ curve around the object (only the object of
interest is inside the curve, everything else is outside).
4.) Locate every point on the boundary of the curve where other ________
touch the object of interest. These are points where
contact forces are exerted on the object.
5.) Name and label each contact force. There is at least one force at each
point of contact.
6.) Name and label each _________________ force acting on the object.
Examples:
(for the box)
(for the person)
(for the car)
(for the car)
(for the truck)