Motion
1 The motion of objects can be
described with the words distance, displacement, speed, velocity, and
acceleration. These terms are
mathematical quantities which are used to describe the motion of
objects
and can be divided into two categories. The quantity is either a vector
or a scalar.
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What is motion? In science we define motion as the change in
position with time. How fast an object changes position or the rate
that an object’s position changes with time is called the speed.
If we know both the direction in which an object moves and its speed,
then the combined direction and speed are called the velocity
of an object. When either the speed or the velocity of an object is
zero, then there is no motion.
These two categories (scalar & vector) can be distinguished
from one another
by their distinct definitions:
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- Scalars are quantities which are fully described by a magnitude
alone. Think of a ruler (scale).
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- Vectors are quantities which are fully described by both a
magnitude
and a direction. Think of a scale with an arrow head (signifying
direction) drawn on it.
2 Distance and displacement are
two quantities which may seem to mean
the same thing, yet they have distinctly different meanings and
definitions.
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- Distance is a scalar quantity which refers to "how
much ground an object has covered" during its motion.
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- Displacement is a vector quantity which refers to "how
far out of place an object is"; it is the object's change
in position.
3 Speed and Velocity. Just as
distance and displacement have distinctly
different meanings (despite their similarities), so do speed and
velocity.
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- Speed is a scalar quantity which refers to "how fast
an object is moving." A fast-moving object has a high speed
while a slow-moving object has a low speed. An object with no movement
at all has a zero speed.
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- Velocity is a vector quantity which refers to "the
rate at which an object changes its position." Imagine a
person moving rapidly - one step forward and one step back - always
returning to the original starting position. While this might result
in a frenzy of activity, it would also result in a zero velocity.
Because the person always returns to the original position, the motion
would never result in a change in position. Since velocity is defined
as the rate at which the position changes, this motion results in
zero velocity. If a person in motion wishes to maximize his/her
velocity,
then that person must make every effort to maximize the amount that
he/she is displaced from his/her original position. Every step must
go into moving that person further from where he/she started. For
certain, the person should never change directions and begin to return
to where he/she started.
4 Acceleration An often
misunderstood quantity, acceleration has a
meaning much different from the meaning sports announcers and other
individuals associate with it. The definition of acceleration is:
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- Acceleration is a vector quantity which is defined as "the
rate at which an object changes its velocity." An object
is accelerating if it is changing its velocity.
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On 24 Nov 2005, 05:13.