1.Impulsive Force
An impulsive force is a very great force acting for a very short time on a body, so that the
change in the position of the body during the time the force acts on it may be neglected.
e.g.The blow of a hammer, the collision of two billiard balls etc.
2.Impulse of a force
The impulse J of a constant force F acting for a time t is defined as
the product of the force and time.
i.e Impulse = Force × time
J = F × t
The impulse of force F acting over a time interval t is defined by the integral.
The impulse of a force, therefore can be visualized as the area under the force versus time
graph as shown in Fig above When a variable force acting for a short interval of time, then the
impulse can be measured as,
J = Faverage × dt
Impulse of a force is a vector quantity and its unit is N s.
Principle of impulse and momentum
By Newton’s second law of motion, the force acting on a body = m a
Where m = mass of the body and a = acceleration then
The impulse of the force = F × t = m a t
If u and v be the initial and final velocities of the body then,
a = v-u/t
therefore, impulse of the force = m * v-u/t * t= mv - mu
i.e. Impulse = Final momentum of the body – initial momentum of the body
i.e. Impulse = Change in momentum
The above equation shows that the total change in the momentum of a body during a time interval is equal to the impulse of the force acting during the same interval of time. This is called principle of impulse and momentum.
Examples
(i) A cricket player while catching a ball lowers his hands in the direction of the ball.
If the total change in momentum is brought about in a very short interval of time, the average
force is very large according to the equation,
By increasing the time interval, the average force is decreased. It is for this reason that a cricket
player while catching a ball, to increase the time of contact, the player should lower his hand in
the direction of the ball, so that he is not hurt.
(ii) A person falling on a cemented floor gets injured more where as a person falling on a sand
floor does not get hurt. For the same reason, in wrestling, high jump etc., soft ground is
provided.
(iii) The vehicles are fitted with springs and shock absorbers to reduce jerks while moving on uneven or wavy roads.
An impulsive force is a very great force acting for a very short time on a body, so that the
change in the position of the body during the time the force acts on it may be neglected.
e.g.The blow of a hammer, the collision of two billiard balls etc.
2.Impulse of a force
The impulse J of a constant force F acting for a time t is defined as
the product of the force and time.
i.e Impulse = Force × time
J = F × t
The impulse of force F acting over a time interval t is defined by the integral.
The impulse of a force, therefore can be visualized as the area under the force versus time
graph as shown in Fig above When a variable force acting for a short interval of time, then the
impulse can be measured as,
J = Faverage × dt
Impulse of a force is a vector quantity and its unit is N s.
Principle of impulse and momentum
By Newton’s second law of motion, the force acting on a body = m a
Where m = mass of the body and a = acceleration then
The impulse of the force = F × t = m a t
If u and v be the initial and final velocities of the body then,
a = v-u/t
therefore, impulse of the force = m * v-u/t * t= mv - mu
i.e. Impulse = Final momentum of the body – initial momentum of the body
i.e. Impulse = Change in momentum
The above equation shows that the total change in the momentum of a body during a time interval is equal to the impulse of the force acting during the same interval of time. This is called principle of impulse and momentum.
Examples
(i) A cricket player while catching a ball lowers his hands in the direction of the ball.
If the total change in momentum is brought about in a very short interval of time, the average
force is very large according to the equation,
By increasing the time interval, the average force is decreased. It is for this reason that a cricket
player while catching a ball, to increase the time of contact, the player should lower his hand in
the direction of the ball, so that he is not hurt.
(ii) A person falling on a cemented floor gets injured more where as a person falling on a sand
floor does not get hurt. For the same reason, in wrestling, high jump etc., soft ground is
provided.
(iii) The vehicles are fitted with springs and shock absorbers to reduce jerks while moving on uneven or wavy roads.
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