Newtons Third Law

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Definition

Newtons third law of motion states that if body A exerts a $F_{AB}$ on body B, then body B will exert an equal and opposite force $F_{BA}$ on body A. #PhysicsDefinitions

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$F_{EB}$ → gravitational force of earth on book $F_{BE}$ → gravitational force of book on earth	$F_{TB}$ → normal force by table on the book $F_{BT}$ → normal force by the book on the table

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Pair of action reaction forces are shown

• gravitational force $F_{EB}$ → exerted by earth on book → and the upward force $F_{BE}$ exerted by book on earth
• Normal force $F_{TB}$ → by table on the book → and the normal force $F_{BT}$ by the book on the table

Each action and reaction pair are equal ⇒ in magnitude but act in opposite directions.

Hence ⇒ force of the table on the book ⇒ does not form an action reaction pair with the weight of the book.

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Newtons third law of motion tells us 4 characteristics of force

1. forces always occur in pairs ⇒ each pair is made up of an action and a reaction force
2. action and reaction forces are equal in magnitude
3. action and reaction forces act in opposite directions
4. action and reaction forces act on different bodies

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How are 2 forces in an action reaction pair identical

• both forces are of same type
• magnitudes of both forces are equal How are 2 forces in an action reaction pair different
• Act in opposite directions
• Act on 2 different bodies

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