NEWTON'S LAWS OF MOTION [ CLASS - 9 ]

NEWTON

NEWTON'S FIRST LAW OF MOTION

This law states everybody continues in its state of rest or of uniform motion in a straight line unless it is compelled by some external force to change that state.

Example 1.

Example 2.

Example 3.

• This law defines force:-
  According to this law , a body at rest or in uniform motion will remain at rest or in uniform motion unless an external force acts upon it. This shows that force is an agency which changes the state of rest or uniform motion. But sometimes a force applied on a body is not able to change its state of rest or of uniform motion.So, force is defined as ' an external agency which changes or tends to the state of rest or of uniform motion in a straight line.
  Hence, this law of motion gives a qualitative definition of force.
• This law defines inertia.
  
• Newton's first law of motion is also called 'the law of inertia.'

NEWTON'S SECOND LAW OF MOTION

The rate of change of linear momentum of a body is directly proportional to the applied force and the change takes place in the direction of the applied force.

• This law gives the measurement of force, F= ma. 
  
  
  
• This law gives the units of force
• SI unit of force is newton
• One newton :- one newton is defined as that much force which produces an acceleration of 1 m/s² in a body of mass 1kg
• In CGS system unit of force is dyne (dyn)
• One dyne is that much force which produces an acceleration of 1cm/s² in a body of mass 1 gram
• This law includes the first law and third law. So, the second law is the real law of motion.
• Example 1.
  
  
  

NEWTON'S THIRD LAW OF MOTION

To every action, there is always an equal and opposite reaction.

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