motion translation
average speed
Rotation
kinematics
center of mass
Center of gravity
gravitational force
Gravity displacement
direction
Vector quantity speed
velocity
Rate
relative motion
acceleration
Rotational motion
Motion – is the change in position and
orientation of an object.
 Translational motion (translation) is the
movement of a rigid object’s center of
mass from one place to another.
 Rotational motion (rotation) is the
movement around a rigid object’s
center of mass.
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
Kinematics is the study of the motion of
objects from one point to another.
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
Linear motion – is movement in a straight
line and is the simplest form of
translational motion.

The linear motion of any rigid object is
described as the motion of its center of
mass.
Center of mass – the point which acts as
though the total mass of the object were
at that point.
 The center of mass of a rigid object is in
the same position as its center of gravity.
 The center of gravity of an object is the
point through which the Earth’s
gravitational force acts on the object.

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Displacement – is the distance and
direction of an object from a fixed
reference point.
 It is a vector quantity.
 The position of an object can be
expressed by its displacement from a
specified point.

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Speed is the ratio of the distance
traveled by an object to the time taken.
 If the speed of an object is constant, it is
said to be moving with uniform speed.
 The average speed of an object over a
time interval is the distance traveled by
the object divided by the time interval.
 The instantaneous speed is the speed at
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any given moment.


Velocity is the speed and direction of an
object (its displacement in a given time).

It is a vector quantity.

Uniform velocity, average velocity and
instantaneous velocity are all defined in
a similar way to uniform speed.
Relative velocity is the velocity which an
object appears to have when seen by
an observer who may be moving.
 This is known as the velocity of the object
relative to the observer.

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Acceleration is the ratio of the change in
velocity of an object to the time taken.
 It is a vector quantity.
 An object accelerates if its speed
changes or its direction of travel
changes.
 Deceleration in one direction is
acceleration in the opposite direction
 (negative acceleration).


An object whose velocity is changing
the same amount in equal amounts of
time is moving with uniform acceleration.
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Rotational motion is the movement of an
object about its center of mass.
 In rotational motion, each part of the
object moves along a different path.
 It must be split into small pieces and the
circular motion of each piece must be
considered separately.

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A sign convention is a method used to
distinguish between motion in opposite
directions.
 The sign convention must be used when
using the equations of motion because
the equations use displacement not
distance, so changes of direction must
be considered.

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