force is an external effort in the form of a push or pull which either changes or tends to change the state of rest or of uniform motion in a straight line.



motion is in a straight line.

force is needed to change the state of rest or of uniform motion.

force is effort....!!!
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INERTIA


this footballer is applying force on the ball to change its state of rest....!!


footballer is applying an external force  to  change the direction and the speed of the moving body............!!!

so inertia is the inherent property of all the objects to not to change their state of rest or of uniform motion along a straight line unless acted upon by an external force.
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INERTIA OF REST



on shaking an apple tree we set the branches into motion.
but the apple remains in its state of rest.
so it gets detached and falls down under the effect of gravity.



THIS PROPERTY is Inertia of rest.........!!
it is the inability of the body to change its state of rest by itself.
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when there is no gravity there is no force acting on the object.
so it will remain in its same state of rest.

tis is Inertia of motion
it cannot change by itself the state of uniform motion along a straight
 line.
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the trucks linear momentum is the product of mass and velocity.
momentum is a vector quantity and its direction is along the direction of velocity.
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NEWTON"S SECOND LAW OF MOTION



the change in momentum takes place in the direction of force.
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two bodies 1 and 2 are present.
whenever body 1 applies a force on body 2 , body 2 applies an equal and opposite forces on each other.

THIS IS WHAT newton's third law basically state.


therefore in this picture
Fb= - Fa

EQUAL in magnitude and opposite in direction.
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