Law of motion

Laws of Motion

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Before studying Law of motion let us perform interesting experiment related to motion 

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A body can have two state 

1) State of rest 

2) State of motion

A branch of physics that deals with study of motion of a body is called as Mechanics.

Mechanics can be further classified as :

a) Kinetics : A branch of mechanics which deals with the study of actual motion of  body is called as Kinetics.

It can be further classified as 

i) Kinematics : The study of various motion without considering its actual cause is called as Kinematics. In kinematics various quantity like velocity, displacement, acceleration is studied.

ii)Dynamics : The study of various motion of a body along with its actual cause is called as Dynamics. In dynamics mechanics various quantity like work, momentum, force, torque, power, etc is studied.

b) Statics : A branch of mechanics which deals with the study of system at rest is called as Statics.

Introduction : In olden times Aristotle thought that a force is necessary for constant motion of a body. It is our daily experience that a body in a motion comes to rest after covering some distance and a force must be continuously supplied to keep body in motion. Galileo was the first person to state that an external force is not required to keep any body in motion in a straight line. After that Newton studied the behaviour and formulated 3 laws of motion. There are various type of motion such as linear, circular, rotational, vibrational, etc. The trajectory of this motion is decided by acceleration a and initial velocity u .

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The trajectory of  a motion :

1) Linear Motion : If initial velocity of body is zero ,acceleration in any direction leads to a linear motion. If initial velocity is non zero, then acceleration must be in line with initial velocity to get a linear motion.

2) Circular motion : if initial velocity is not zero, then acceleration perpendicular to it causes circular motion.

3) Parabolic motion : If acceleration is constant and initial velocity is not in line with acceleration results in parabolic trajectory.

Newton First Law: Newton first law stated that every body continues to be in a state of rest or uniform motion along straight line, unless it is acted by an external unbalanced force.

Importance of Newton’s First Law of Motion:

1) It explains the equilibrium between state of rest and state of motion because both system requires an unbalanced external force to change their state.

2)It gives actual definition of force .i.e force is any physical quantity which brings about change in the state of an object.

3)It defines inertia as a property of an object by virtue of which it opposes the change in its state. It is measure of a mass of an object.

Newton Second Law: Newton second law stated that the rate of change of linear momentum of a body is directly proportional to the external unbalance force applied on the body and take place in the direction of force.

Newton Third Law: Newton third law stated that to every action there is always an equal and opposite reaction.

Type of force: 

 

Gravitational Force: If we throw a body upward ,it falls back to the earth after covering certain distance. This show that the earth exerts a force of attraction on the body. The existence of the force of attraction between a body and the earth is universal. This force is called a gravitational force. Between two point masses (particles) separated by a given distance, this is the weakest force having infinite range. This force is always attractive. Structure of the universe is governed by this force.

Characteristics : 

1) This force is always an attractive and applicable for microscopic and microscopic bodies. 

2)  Obeys inverse square law of distance.

3) Does not depend on intervening medium.

Examples :

1) The motion of a planet around the sun, Motion of satellite around the planet.

2) The weight of a body is due to gravitational force exerted by the earth on the body.

Electromagnetic force: The force between electric charges  in relative motion are called as electromagnetic forces. Electromagnetic forces are stronger than that of gravitational forces. The force which holds together the atoms ans molecules of a body is called electromagnetic force.

Characteristics : 

1) Obey inverse square law of distance.

2) Depends on intervening medium.

Strong Nuclear Force: Strong nuclear force is an attractive force between proton and neutron that keep nucleus together.

Characteristics : 

1) It is strongest force in nature.

Weak Nuclear Force ; weak nuclear force is an mechanismo of interaction subatomic particles  that is responsible for the radioactive decay of atoms.

Characteristics :

1)It is act between any two elementary particles.

2) It is much weaker than strong nuclear forces.

3) It is stronger than the gravitational force.

4) It range is very short of the order of size of the medium.

│<<<Conservation of linear momentum>>>│

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