Newton's Third Law
Must satisfy TWO conditions:
1. equal in magnitude but opposite in direction
2.
the forces MUST INVOLVE the SAME TWO OBJECTS
NOTE: The two forces in an action-reaction pair act on DIFFERENT BODIES
The BIG FIVE
Normal Force
Contact force
(1) of an object to the surface
that's
(2) perpendicular to the surface
NOTE:
N and g
MAY NOT BE EQUAL
(especially in
inclined plane
)
Friction
Contact force that's
parallel to the surface
Kinetic Friction
is
less than or equal
to
Static Friction
Static Friction has
max magnitude
Inclined Planes
NOTE:
The
Net Force
of a System is the
TOTAL force of MOVING (dynamic) OBJECTS
In Inclined Planes, the Net Forces is
Fx - Ff
, since the object moves
horizontally
--->
no vertical motions
Pulley
The image is an
Easy way to find acceleration in system
(particularly pulley)
For Pulley,
every OBJECT (weight) has its OWN Free Body Diagram
(F = ma)
Uniform Circular Motion (UCM)
Alternative centripetal acceleration formula
a = (4 PI^2 R) / T
T =
t for 1 revolution
(time)
NOTE:
__UCM is
not EQUILIBRIUM
(because
a is not constant
)
__ Any force that points toward the center of a circle is
positive
and vice versa
UCM (II)
UCM can result from
ANY
combination of forces, so that the net force is always directed towards the center of the circle and has a
constant
magnitude
VD: Tension, friction gravity (
real forces
)
Newton's 2nd law Problem-solving Strategy
1. Draw the free-body diagram for EACH objects
2. Find the net force formula F = ma for EACH objects
3. Choose x, y components for EACH body
4. CONNECT the formula of each bodies
(usually they have the same
acceleration
)
NOTE:
If bodies are
Connected by
Fluid Resistance