Introduction :
In 1684, encouraged by his friend Edmund Halley, Sir Isaac Newton embarked on writing what was to be The principia mathematica was one of the greatest scientific works ever published. He enunciated the three laws of motion and the universal law of gravitation, which explained all the three Kepler's laws of planetary motion.
In earlier times, motion of bodies was studied by philosophers. Most philosophers believed that a body moved with uniform velocity due to some external agent. They also thought that if there were no external agent the body would naturally come to rest. Galileo was the first to show that some external force was necessary to change the velocity of a body but that no external force was necessary to maintain the velocity of a body. This principle was adopted by Newton in his first law of motion.
Sir Issac Newton first law:
The law enables us to define inertia and force. From this law it can be concluded that if the net external force on an object is zero, the acceleration of the object is zero.
Inertia ; If the net external force is zero, a body at rest continues to be at rest and a body in motion continues to move with uniform velocity. This property is called inertia. It is the resistance to change the state of uniform motion. Mass is a measure of inertia. Ex: when the bus stops suddenly our feet stop due to the friction. But the rest of the body continues to move forward due to inertia of motion.
Force : It is the physical quantity that changes or tries to change the state of rest or of uniform motion along a straight line.
Sir Issac Newton second law:
By Newton first law of motion, when there is no net external force on a body it moves with uniform velocity. In terms of momentum, the body will have constant momentum when there is no net external force on a body, Hence, when the momentum of a body changes the body must be under the action of a net external force.
Newton's second law of motion states that " The rate of change of momentum of a body is directly proportional to the resultant or net external force action on the body and takes place in the direction in which the force acts" .
A body of mass m moving with velocity v is under the action of a net external force F in the direction of velocity. If its velocity is increased by `Deltav` in a time interval `Deltat` then by the second law
F `prop` dp /dt (or) F `prop` d/dt (mv) (since p = mv)
F = k d/dt (mv) , Assuming that the mass of the body is constant
F = k m dv/dt = k m a , which shows that the net force is proportional to the product of mass and acceleration.
The proportional constant k is made equal to one, by properly selecting the unit of force. The SI unit of force is newton which is defined as the force that causes an acceleration for 1 ms-2 on a body of mass 1 kg. Substituting k = 1 in F = k m a , we get
F = m a .
The dimensional formula of force is [MLT-2] .
In this statement, action and reaction are nothing but forces. When we hit a wall we apply some force on the wall. An equal and opposite force acts on us due to the wall at the same instant of time. When we walk on the road we push the road backward and the road applies an equal and opposite force on us so that we can move forward. Newton's third law is not strictly applicable when the interaction between two bodies separated by a large distance is considered.
In 1684, encouraged by his friend Edmund Halley, Sir Isaac Newton embarked on writing what was to be The principia mathematica was one of the greatest scientific works ever published. He enunciated the three laws of motion and the universal law of gravitation, which explained all the three Kepler's laws of planetary motion.
In earlier times, motion of bodies was studied by philosophers. Most philosophers believed that a body moved with uniform velocity due to some external agent. They also thought that if there were no external agent the body would naturally come to rest. Galileo was the first to show that some external force was necessary to change the velocity of a body but that no external force was necessary to maintain the velocity of a body. This principle was adopted by Newton in his first law of motion.
Sir Issac Newton first law:
The law enables us to define inertia and force. From this law it can be concluded that if the net external force on an object is zero, the acceleration of the object is zero.
Inertia ; If the net external force is zero, a body at rest continues to be at rest and a body in motion continues to move with uniform velocity. This property is called inertia. It is the resistance to change the state of uniform motion. Mass is a measure of inertia. Ex: when the bus stops suddenly our feet stop due to the friction. But the rest of the body continues to move forward due to inertia of motion.
Force : It is the physical quantity that changes or tries to change the state of rest or of uniform motion along a straight line.
Sir Issac Newton second law:
By Newton first law of motion, when there is no net external force on a body it moves with uniform velocity. In terms of momentum, the body will have constant momentum when there is no net external force on a body, Hence, when the momentum of a body changes the body must be under the action of a net external force.
Newton's second law of motion states that " The rate of change of momentum of a body is directly proportional to the resultant or net external force action on the body and takes place in the direction in which the force acts" .
A body of mass m moving with velocity v is under the action of a net external force F in the direction of velocity. If its velocity is increased by `Deltav` in a time interval `Deltat` then by the second law
F `prop` dp /dt (or) F `prop` d/dt (mv) (since p = mv)
F = k d/dt (mv) , Assuming that the mass of the body is constant
F = k m dv/dt = k m a , which shows that the net force is proportional to the product of mass and acceleration.
The proportional constant k is made equal to one, by properly selecting the unit of force. The SI unit of force is newton which is defined as the force that causes an acceleration for 1 ms-2 on a body of mass 1 kg. Substituting k = 1 in F = k m a , we get
F = m a .
The dimensional formula of force is [MLT-2] .
Sir Issac Newton third law:
Newton's third law tells us about the origin of the force that causes acceleration. It states that " to every action, there is always an equal and opposite reaction " .In this statement, action and reaction are nothing but forces. When we hit a wall we apply some force on the wall. An equal and opposite force acts on us due to the wall at the same instant of time. When we walk on the road we push the road backward and the road applies an equal and opposite force on us so that we can move forward. Newton's third law is not strictly applicable when the interaction between two bodies separated by a large distance is considered.
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