Aristotle Law (Part - 1) - Laws of Motion, Physics Video Lecture - Class 11

hello friends this video on laws of
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topics which we'll cover in this lesson
are introduction Aristotle's fallacy the
law of inertia Newton's first law of
motion Newton's second law of motion
Newton's third law of motion
conservation of momentum equilibrium of
a particle common forces in mechanics
circular motion and solving problems in
mechanics let's think of what causes
motion we have already discussed in our
previous lessons that motion is nothing
but change in position of an object with
respect to time correct so what causes
an object to move an external force is
needed to make a stationary body move
you think of any common example around
you for example you have a ball the ball
will stay at rest until and unless an
external force is applied or it just now
we saw that this ball was pushed by the
hand because of which it started rolling
that means
this external force which is given by
the hand made the ball to move that
means the motion of the ball was caused
due to an external force applied by the
hand similarly we need an external force
to stop a moving body let us suppose a
ball is rolling it will come to stop or
it will come to rest only when the force
produced by the hand will try to stop it
means an external force external force
is the cause of motion an external force
can make a body which is at rest to move
it can also cause a moving body to come
to rest so here we found that force
causes our stationary body to move and a
moving body to come to rest but what
about uniform motion uniform motion I
hope all of you are aware of what is
uniform motion uniform motion means a
body is moving with constant velocity
that means the velocity of the body is
same throughout the journey so in case
of a body moving with uniform velocity
that time we do not exactly see some
force acting on it or whether there is a
force which is acting on it so what is
the physics behind or what is the cause
of motion of uniform in case of uniform
motion so in the next slide we will
discuss the cause of uniform motion the
first law which was given to describe
the cause behind uniform motion was
given by Aristotle which is popularly
known as Aristotle's law of uniform
motion this law stated that an external
force is required to keep a body in
uniform motion that means when a body is
a uniform motion an external force has
to be present continuously that means as
long as an external force is present on
a body the body will be in uniform
motion so how did a distorter come to
this conclusion and a startle basically
thought of such as an a globe let us
suppose this is Ronnie and this is a box
which Ronnie ties to a string correct so
this is the box Ronnie died
string to the box and what he is doing
here instead he is just walking and
pushing the string that means he is
applying some force what was happening
was he applied some force because of
which the box was also moving after some
time he left the thread he is no more
holding the thread the box comes to rest
even though Ronnie is moving observe it
once again in this case Ronnie is
holding the thread tied to the box and
he is dragging it now he leaves the
thread and box off the body stops moving
that means initially the body was in
motion as soon as the force was left or
the force was taken back the body came
to rest
so Aristotle concluded from such country
from such observation that an external
force is continuously needed to keep a
body in uniform motion if a body is in
uniform motion that means there is a
force which is acting on it
so in brief that is what Aristotle's law
conveyed but after some time it was
observed that the a distorted law proved
out to be false so what was a distorted
fantasy I mean where did a distorted
film a distorted slow said that an
external force is required to keep a
body in uniform motion right so that is
what we had observed he dragged the Box
when he left it the Box stopped moving
but it was later observed that this
scenario which happened here or which
Aristotle observed it proves something
else the box was moving initially
whenever a box is lying on a ground
there is a force which is acting at the
surface of contact that is at this point
like suppose let us consider the
scenario from here right now the box is
at rest
whenever the boxes are pressed there is
a force of friction with
acting between the surface of the box
and the flow so there is a force of
friction which always opposes motion it
doesn't want that the body should move
right now this guy in order to make the
box means he is applying a force in this
direction now when this force when this
force is greater than the frictional
force then the body is moving till this
point now when he leaves giving this
force that means this force becomes
equal to zero at this point but this
force that is the frictional force is
still acting so in this case the
frictional force becomes greater than
the force applied because the force
applied is zero therefore it opposes
motion and frictional force of causes
motion so the body comes to rest so what
did we see in this scenario the external
it was not that the external force kept
the body in uniform motion external
force was needed to make the body move
and when the external force was taken
aback due to friction the body came to
rest so the entire the major role in
making the body move and stopping the
body was played by the frictional force
so the conclusion was that an external
force is required to keep a body in
uniform motion only if the resistive
forces like frictional force or viscous
forces are present thank you visit exam
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