PHYSICS NOTES 9TH CLASS
Written by BILAL HASAN B.cs , M.cs..
NICE STUDIES ACADEMY
Circular Motion and Gravitation 9th physics notes
Circular Motion and Gravitation 9th physics notes
DEFINITIONS
Centripetal Force
Definition
"The force that causes an object to move along a curve (or a curved path) is called centripetal force."
Mathematical Expression
We know that the magnitude of centripetal acceleration of a body in a uniform circular motions is directly proportional to the square of velocity and inversely proportional to the radius of the path Therefore,
a(c) < v2 (Here < represents the sign of proportionality do not write this in your examination and 2 represents square of v)
a(c) < 1/r
Combining both the equations:
a(c) < v2/r
From Newton's Second Law of Motion:
F = ma
=> F(c) = mv2/r
Where,
* Fc = Centripetal Force
* m = Mass of object
* v = Velocity of object
* r = Radius of the curved path
Factors on which Fc Depends:
Fc depends upon the following factors:
* Increase in the mass increases Fc.
* It increases with the square of velocity.
* It decreases with the increase in radius of the curved path.
Examples
* The centripetal force required by natural planets to move constantly round a circle is provided by the gravitational force of the sun.
* If a stone tied to a string is whirled in a circle, the required centripetal force is supplied to it by our hand. As a reaction the stone exerts an equal force which is felt by our hand.
* The pilot while turning his aeroplane tilts one wing in the upward direction so that the air pressure may provide the required suitable Fc.
Centrifugal Force
Definition
"A force supposed to act radially outward on a body moving in a curve is known as centrifugal force."
Explanation
Centrifugal force is actually a reaction to the centripetal force. It is a well-known fact that Fc is directed towards the centre of the circle, so the centrifugal force, which is a force of reaction, is directed away from the centre of the circle or the curved path.
According toNewton
Examples
* If a stone is tied to one end of a string and it is moved round a circle, then the force exerted on the string on outward direction is called centrifugal force.
* The aeroplane moving in a circle exerts force in a direction opposite to the pressure of air.
* When a train rounds a curve, the centrifugal force is also exerted on the track.
Law of Gravitation
Introduction
Newton
Statement
Every body in the universe attracts every other body with a force, which is directly proportional to the product of masses and inversely proportional to the square of the distance between their centres.
Mathematical Expression
Two objects having mass m1 and m2 are placed at a distance r. According toNewton
F < m1m2 ((Here < represents the sign of proportionality do not write this in your examination)
Also F < 1/r2 (Here 2 represents square of r)
Combining both the equations :
F < m1m2/r2
Removing the sign of proportionality and introducing a constant:
F = G (m1m2/r2)
Centripetal Force
Definition
"The force that causes an object to move along a curve (or a curved path) is called centripetal force."
Mathematical Expression
We know that the magnitude of centripetal acceleration of a body in a uniform circular motions is directly proportional to the square of velocity and inversely proportional to the radius of the path Therefore,
a(c) < v2 (Here < represents the sign of proportionality do not write this in your examination and 2 represents square of v)
a(c) < 1/r
Combining both the equations:
a(c) < v2/r
From Newton's Second Law of Motion:
F = ma
=> F(c) = mv2/r
Where,
* Fc = Centripetal Force
* m = Mass of object
* v = Velocity of object
* r = Radius of the curved path
Factors on which Fc Depends:
Fc depends upon the following factors:
* Increase in the mass increases Fc.
* It increases with the square of velocity.
* It decreases with the increase in radius of the curved path.
Examples
* The centripetal force required by natural planets to move constantly round a circle is provided by the gravitational force of the sun.
* If a stone tied to a string is whirled in a circle, the required centripetal force is supplied to it by our hand. As a reaction the stone exerts an equal force which is felt by our hand.
* The pilot while turning his aeroplane tilts one wing in the upward direction so that the air pressure may provide the required suitable Fc.
Centrifugal Force
Definition
"A force supposed to act radially outward on a body moving in a curve is known as centrifugal force."
Explanation
Centrifugal force is actually a reaction to the centripetal force. It is a well-known fact that Fc is directed towards the centre of the circle, so the centrifugal force, which is a force of reaction, is directed away from the centre of the circle or the curved path.
According to
Examples
* If a stone is tied to one end of a string and it is moved round a circle, then the force exerted on the string on outward direction is called centrifugal force.
* The aeroplane moving in a circle exerts force in a direction opposite to the pressure of air.
* When a train rounds a curve, the centrifugal force is also exerted on the track.
Law of Gravitation
Introduction
Statement
Every body in the universe attracts every other body with a force, which is directly proportional to the product of masses and inversely proportional to the square of the distance between their centres.
Mathematical Expression
Two objects having mass m1 and m2 are placed at a distance r. According to
F < m1m2 ((Here < represents the sign of proportionality do not write this in your examination)
Also F < 1/r2 (Here 2 represents square of r)
Combining both the equations :
F < m1m2/r2
Removing the sign of proportionality and introducing a constant:
F = G (m1m2/r2)
Centripetal force depends on the velocity,radius and gravity.This force is the reason of the cycle riders to inclined on the roadside when they turn on the round corners.
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