I've given a detailed analysis and notes typed in Ms word of class 11 physics chapter 4 named laws of motion. In these notes there are everything to learn for a competitive or school level exam
● Aristotelian law of motion can be stated as : An external force is
required to keep a body in motion
● Galileo disproved this by experiments using inclined planes.
GALILEO’S EXPERIMENTS
Using single inclined plane
● Galileo studied motion of objects on an inclined plane.
● Objects
1. moving down an inclined plane accelerate
2. objects moving up retard
3. Motion on a horizontal plane is an intermediate situation.
● Galileo concluded that an object moving on a frictionless horizontal
plane should move with constant velocity.
Using Double inclined plane
, ● A ball released from rest on one of the planes rolls down and climbs
up the other.
● When friction is absent, the final height of the ball is the same as its
initial height.
● If the slope of the second plane is decreased and the experiment
repeated, the ball will still reach the same height, but it will travel a
longer distance.
● When the slope of the second plane is zero (i.e., is a horizontal) the
ball travels an infinite distance.
● If there were no friction, the ball would continue to move with a
constant velocity on the horizontal plane.
● Thus, according to Galileo, the state of rest and the state of uniform
linear motion (motion with constant velocity) are equivalent.
● If the net external force is zero, a body at rest continues to remain at
rest and a body in motion continues to move with a uniform velocity.
NEWTON’S LAWS OF MOTION
● Starting from Galileo’s ideas, Newton formed three laws of motion.
NEWTON’S FIRST LAW OF MOTION – THE LAW OF INERTIA
● Everybody continues to be in its state of rest or of uniform
motion in a straight line unless compelled by some external
, force to act otherwise.
INERTIA
● The inability of a body to change its state of rest or uniform motion
along a straight line.
● Inertia means resistance to change.
Inertia of rest (static inertia)
● The property of an object by virtue of which it remains in its state of
rest.
● Example:
1. a person standing in a bus tends to fall backward when the
bus starts suddenly
2. Fruits fall down due to inertia of rest when the branches of
a tree are shaken
3. Dust particles on a carpet fall if we beat the carpet with a
stick
4. With a quick pull, a table cloth can be removed from a
dining table without disturbing dishes on it due to the Inertia
of rest.
Inertia of motion (kinetic inertia)
● The property by which it remains in state of motion
1. A person in running bus , falls forward the bus when stops suddenly.
2. Athlete taking a short run before a jump.
Forces on a book at rest on a horizontal surface
, The two forces are
i) the force due to gravity (i.e., its weight W) acting downward
ii) the upward force on the book by the table, the normal force R.
● Since the book is rest the net force on the book must be zero.
Forces on a car
● When the car is stationary, there is no net force acting on it.
● During pick-up, it accelerates. It is the frictional force that accelerates
the car as a whole.
● When the car moves with constant velocity, there is no net external
force.
● Friction on the front wheels opposes the spinning, so friction must
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