Download Unit 3: FORCE

Unit 3: FORCE
A. A force is that which affects the motion of a
body.
B. All known physical interactions of matter
occur through four fundamental forces: Gravitation,
Electromagnetism, Strong Nuclear Force and Weak
Nuclear Force.
1. The most pervasive force is gravitation,
in that every particle of matter attracts every other
particle.
C. Newton’s Second Law: The acceleration
of a body is directly proportional to the resultant
external force acting on the body, is inversely
proportional to the mass of the body, and has the
same direction as the resultant force.
D. Newton’s Third Law: (Law of Interaction)
If one body exerts a force on another body, then the
second body must exert a force equal in magnitude
but opposite in direction on the first body.
E. Newton’s Universal Law of Gravitation:
Every body in the universe attracts every other body
with a force directly proportional to the product of
their masses and inversely proportional to the square
of the distance between them.
3.2 Buoyant Force
A. Archimedes Principle: Any object
submerged or floating in a fluid is buoyed upward by
a force equivalent to the weight of the fluid it
displaces.
3.3 Friction
A. The friction forces between two objects
depends on the materials from which they are
constructed and the force with which they are pressed
together.
1. Contact between irregularities on the
surfaces of objects obstructs motion.
2. Kinetic (sliding) friction is less than
static (at rest) friction.
3. Static friction is a force tangential to the
surfaces, exerted by one surface on another when the
two surfaces are not sliding past each other.
4. Kinetic friction is similar, but occurs
only when the two surfaces are sliding past each
other.
3.4 Torque
A. A torque is a force applied at a location on a
body and in a direction necessary to cause rotation of
that body.
1.
“torquere” = twist
2. The torque about a given axis or
fulcrum is the product of the force (F) and the lever
arm (L). This product is called the moment of the
force. The lever arm is the perpendicular distance
from the axis of rotation to the line of force
B. A simple machine such as a lever does not
change the amount of work you must do, but it allows
you to do the work using a smaller force.
C. In a first class lever, the fulcrum is always
between the effort and the resistance.
1. First class levers may be used to gain
speed, force or change direction.
D. In a second class lever, the resistance is
always between the fulcrum and the effort.
1.
Second class levers may be used to gain
force.
E. In a third class lever, the effort is always
between the fulcrum and the resistance.
1. A third class lever can only be used to
gain speed.