We were discussing the importance of friction i.e. positive
and negative effects of friction, classifications
of friction, coulomb's
law of dry friction, some guidelines for solving frictional
problems, concept of rolling resistance or rolling friction,
wedge
friction and concept of self- locking and the minimum stopping distance for a vehicle in engineering mechanics with the help of our previous
posts.
Now, we will be interested further to understand here
a very important concept in engineering mechanics i.e. Instantaneous center of zero velocity with the help of this
post.
Instantaneous center of zero velocity
Instantaneous center of zero velocity is basically
defined as the point about which a body appears to be rotating at any given
instantaneous or instant. It will have zero velocity and there will be only one
instantaneous center per body per instant of time.
Instantaneous center of zero velocity acts like absolute center of rotation at the instant considered. we must note it here that it will not be a fixed point in a body nor a fixed point in a plane.
Let us consider a rigid body having a plane motion. There
will be one linear component of translation motion and also rotary motion as
displayed here in following figure.
VA is the absolute velocity of a point and ω
is the rotational velocity of the body. We must note it here that these two
quantities i.e. absolute velocity and rotational velocity will define the
velocity of all other points in the body.
Let us consider the two arbitrary points i.e. point A
and point B and the absolute velocity VA and VB
respectively. Now we will determine here the instantaneous center of zero
velocity.
Let us see here how we will determine the instantaneous center of zero velocity
Instantaneous center of zero velocity could be found
by drawing perpendiculars from these velocities. We have drawn the perpendiculars
from these velocities and we can see in the following figure that these
perpendiculars are meeting with each other at a point C.
This point C will be known as instantaneous center of
zero velocity.
We can also determine the angular velocity from here
with the help of following figure.
ω = VA / rA = VB / rB
Let us see here how we will determine the instantaneous center of zero velocity when velocities are parallel, same in directions but not equal in magnitudes
Let us consider the two arbitrary points i.e. point A
and point B and their absolute velocity VA and VB
respectively. Let us assume that these velocities are parallel, same in
directions and not equal in magnitude as displayed here in following figure.
Now we will determine here the instantaneous center of
zero velocity for above mentioned case.
Instantaneous center of zero velocity could be found
by drawing the lines joining the tip and the base of these velocities. These lines
will intersect or meet with each other at a point C which will be termed as instantaneous center of zero velocity.
When the parallel velocities will become equal in
magnitude, the instantaneous center will be pushed further and will approach to
infinity and hence there will be a pure translation motion.
Let us see here how we will determine the instantaneous center of zero velocity when velocities are parallel and opposite in directions
Let us consider the two arbitrary points i.e. point A
and point B and their absolute velocity VA and VB
respectively. Let us assume that these velocities are parallel but opposite in
directions as displayed here in following figure.
Now we will determine here the instantaneous center of
zero velocity for above mentioned case.
Instantaneous center of zero velocity could be found
by drawing the lines joining the tip and the base of these velocities. These lines
will intersect or meet with each other at a point C which will be termed as instantaneous center of zero velocity.
Therefore, we have seen here what is the basics of instantaneous center of zero velocity and we have also secured the information to determine
the instantaneous center of zero velocity.
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We will find out now the concept of in our next
post.
Reference:
Engineering Mechanics, By Prof K. Ramesh
Image courtesy: Google
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