Transcript Linear motion

Motion
By
Dr. Ajay Kumar
Concept
• In physics, motion is a change in position of an
object with respect to time.
• Change in action is the result of an
unbalanced force.
• Motion is typically described in terms of
velocity, acceleration, displacement and time .
Cont.
• An object's velocity cannot change unless it is acted
upon by a force, as described by Newton's first law.
• An object's momentum is directly related to the
object's mass and velocity, and the total momentum
of all objects in a closed system (one not affected by
external forces) does not change with time, as
described by the law of conservation of momentum.
Cont.
• A body which does not move is said to be at
rest, motionless, immobile, stationary, or to
have constant (time-invariant) position.
Cont.
• Motion is always observed and measured relative to
a frame of reference.
• As there is no absolute frame of reference, absolute
motion cannot be determined; this is emphasised by
the term relative motion.
• A body which is motionless relative to a given
reference frame, is still moving relative to infinitely
many other frames. Thus, everything in the universe
is moving.
Cont.
• Linear motion is motion along a straight line, and can
therefore be described mathematically using only
one spatial dimension.
• The linear motion can be of two types, Uniform
Linear motion, with constant velocity or zero
acceleration.
• Non Uniform Linear motion, with variable velocity or
non-zero acceleration.
• The motion of a particle (a point-like object)
along a line can be described by its position x,
which varies with t (time). Linear motion is
also called as rectilinear motion.
• Linear motion is the most basic of all the motions.
• According to Newton's first law of motion, objects
that not subjected to forces will continue to move
uniformly in a straight line indefinitely.
• Under every-day circumstances, external forces such
as gravity and friction will cause objects to deviate
from linear motion and can cause them to rest at a
point.
Definition
• Translation or linear motion occurs if all parts
of a body moves the same distance at the
same time in the same direction.
• For example: If a block is pushed on a
horizontal surface. The block will undergo
translation motion only.
• Another typical example of translation motion
is the vertical motion of a lift in a shaft.
• Another form of translation motion is
curvilinear motion in which the object moves
in a curved path but necessarily a circular
pathway.
Rotational Motion - Concept
• Rotation around a fixed axis is a special case
of rotational motion.
• The fixed axis hypothesis exclude the
possibility of a moving axis, and cannot
describe such phenomena.
Definition
• Rotational or angular motion occurs when a
body moves in a circular path such that all
parts of the body moves through the same
angle at the same time.
• The angular motion occurs about a central
line known as the axis of rotation which lies
perpendicular to the plane of motion.
Cont.
• For example : a gymnasts doing giant circle
the center of gravity of the gymnast may
undergo rotational motion with the centerline
of the bar acting on the axis of rotation of the
motion.
General Motion – Concept & Definition
• The third class of motion is called the general
motion which occurs if a body undergo
translation and rotational motion
simultaneously.
• This motion is more complex to analyse as
compared to pure translation or pure
rotational motion.
• The diver is an example of a motion
undergoing general motion.
• Most human body segmental motion are of
general type of motion.
• For example : while walking the lower
extremities both translate and rotate.
Cont.
• The branch of kinematics that deal with the
description of the translation motion is known
as linear kinematics, and the branch that deals
with the rotational motion is angular
kinematics.