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MOTION &
FORCES
VOCABULARY
MOTION
The process of continual
change in the physical
position of an object
(distance) relative to
reference point ;
With direction 
N-S-E-W, up-down
SPEED
The ratio of the distance
traveled by an object
(regardless of its direction) to
the time required to travel
that distance.
Speed = distance / time
VELOCITY
The speed and direction of
motion of a moving body; the
rate of change of its position
in a particular direction with
time.
DIRECTION MATTERS !
ACCELERATION
The time rate of change of the
velocity of a moving body
with respect to magnitude or
direction; the derivative of
velocity with respect to time.
A = Vfinal – Vinitial / time
FORCE
A push or a pull exerted on an
object in order to change the
motion of the objects;
force has size and direction.
F=mxa
NEWTON (N)
The SI derived unit used to
measure force.
One newton is equal to the
force needed to accelerate a
mass of one kilogram one
meter per second per second.
FRICTION
A force on objects or substances in
contact with each other that
resists motion of the objects or
substances relative to each
other; a resistance encountered
when one body moves relative to
another body with which it is in
contact.
GRAVITY
The force of attraction by
which terrestrial bodies tend
to fall toward the center of
the Earth; the fundamental
force of attraction that all
objects with mass have for
each other.
WEIGHT
The force that gravitation exerts
upon a body, equal to the mass
of the body times the local
acceleration of gravity
Depends on its mass & the
strength of the gravitational pull.
The SI unit of weight is the
newton.
MASS
A measure of the amount of matter
contained in or constituting a
physical body.
The mass of an object is related to the
force required to accelerate it and
hence is related to its inertia, and is
essential to Newton's laws of motion.
In most scientific applications, the SI
unit of kilogram is used.
FREE FALL
Free descent of a body in
which the gravitational force
is the only force acting on it.
A satellite in orbit is in free fall,
as is a skydiver (if we neglect
the effects of air resistance).
INERTIA
The resistance of a body to
changes in its momentum.
Because of inertia, a body at rest
remains at rest, and a body in
motion continues moving in a
straight line and at a constant
speed, unless it is acted upon by
an external force is applied to it.
MOMENTUM
A vector quantity that expresses the
relation of the velocity of a body,
wave, field, or other physical system,
to its energy.
The direction of the momentum of a
single object indicates the direction
of its motion. Momentum is a
conserved quantity (it remains
constant unless acted upon by an
outside force.
PROJECTILE MOTION
The curved path that an object
follows when thrown,
launched, or otherwise
projected near the surface of
Earth.
AIR RESISTANCE
The opposition of the
atmosphere to forward
movement;
also called aerodynamic drag.