Newton;S Third Law

A force is a push or pull upon an object which results from its interaction with another object. According to Newton, whenever objects A & B interact with each other , they exert forces upon each other. When you in your chair, your body exerts a downward force on the chair & the chair exerts an upward force on your body. There are two forces resulting from this interaction– a force on the chair & a force on your body. These two forces are called ACTION & REACTION forces &are the subject of Newton’s third law of motion.

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first objects EQUALS the size of the force on the second object. The direction of the force on the first object is OPPOSITE to the direction of the force on the second object. Force ALWAYS come in pairs- equal & opposite action-reaction force pairs.

EXAMPLES OF ACTION- REACTION FORCE

(FOR FISHES)A variety of action- reaction force pairs are evident in nature.

Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forward, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards) . For every action, there is an equal (in size) & opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim.

FLYING MOTION OF BIRDS

Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. Since forces results from mutual interactions, the air must also be pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). For every action , there is an equal (in size) and opposite (in direction) reaction. Action- reaction force pairs make it possible for birds to fly.

• Important provision: two objects must be involved! There exits a whole set of situations where two equal & opposite act on the same object, canceling each other so that no acceleration (or even no motion) occurs. This is not an example of the third law, but of equilibrium between forces.

Newton’s 3rd law can be illustrated by identifying the pairs of forces which are involved in supporting the blocks on the spring scale.

This law does not address the issue of force & acceleration applied to a body like first two laws.

The law characterizes the nature of force irrespective of its class & genesis that they exist in pair of two equal but opposite forces. The existence of a single force is impossible.

The pair of forces acts on two different bodies.The two forces do not neutralize each other, because

they operate on different bodies. Each of the bodies will accelerate, if free to do so.

The information used in this presentation is taken from:

Google.comBook of science and technologyThe pictures used in this presentation are taken from:Google.comYahoo.comNature’s gallery.comI would also like to thank my science teacher, my

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