Laws of Motion 1 Flashcards
what is newton’s first law of motion
Every body 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.
what happens when acceleration is 0
If the net external force on a body is zero, its
acceleration is zero. Acceleration can be non
zero only if there is a net external force on
the body.
what is inertia in
it is the tendency of the body to continue its state of rest or motion in a straight line
Inertia is the inherent property of a body that makes it oppose any force that would cause a change in its motion.
what are three types of inertia
1) Inertia of motion
when we are in a moving car,we move font
2) Inertia of rest
when we are at a stationary car and it starts moving suddenly, we move back
3) Inertia of direciton
when we are taking a turn, we move tangentially
Suppose we
are standing in a stationary bus and the driver
starts the bus suddenly. We get thrown
backward with a jerk. Why ?
Our feet are in touch
with the floor. If there were no friction, we would
remain where we were, while the floor of the bus
would simply slip forward under our feet and the
back of the bus would hit us. However,
fortunately, there is some friction between the
feet and the floor. If the start is not too sudden,
i.e. if the acceleration is moderate, the frictional
force would be enough to accelerate our feet
along with the bus. But our body is not strictly
a rigid body. It is deformable, i.e. it allows some
relative displacement between different parts.
What this means is that while our feet go with
the bus, the rest of the body remains where it is
due to inertia. Relative to the bus, therefore, we
are thrown backward. As soon as that happens,
however, the muscular forces on the rest of the
body (by the feet) come into play to move the body
along with the bus.
An astronaut accidentally
gets separated out of his small spaceship
accelerating in inter stellar space at a
constant rate of 100 m s-2. What is the
acceleration of the astronaut the instant after
he is outside the spaceship ? (Assume that
there are no nearby stars to exert
gravitational force on him.)
Since there are no nearby stars to exert
gravitational force on him and the small
spaceship exerts negligible gravitational
attraction on him, the net force acting on the
astronaut, once he is out of the spaceship, is
zero. By the first law of motion the acceleration
of the astronaut is zero.
what is momentum
Momentum, P of a body is defined to be the
product of its mass m and velocity v, and is
denoted by p:
p = m v (5.1)
Momentum is clearly a vector quantity.
it refers to thequantity of the motion contained in a body
it is used to determine the impact made by the body
what is the second law of motion? law of dynamics
The rate of change of momentum of a body is
directly proportional to the applied force and
takes place in the direction in which the force
acts.
what is impulse
it is the effect of a force for a very short interval of time. it is measured as the product of force and the interval of time for which the force is acting
what is impulsive force
A large force acting for a short time to produce a
finite change in momentum is called an impulsive
force.
