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Newton's Third Law

# Newton's Third Law

Newton’s Third Law concerns equal and opposite forces. This video shows how this works in two real life situations involving skateboarders, and rockets.

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Key learning points:

• Newton's Third Law is that "If A exerts a force on B, B exerts an equal but opposite force on A".
• Forces always occur in "Newton pairs" - an action force and an equal reaction force in the opposite direction.
• In a rocket, the propellant (e.g. burning gas) is forced backwards (action), so there is forward force on the rocket (reaction).
• Newton's Second Law is that the acceleration of an object is directly proportional to the unbalanced force and inversely proportional to its mass.
• Newton's Second Law can be written as F=ma.
• If the force on an object remains constant but its mass increases, its acceleration will decrease.

BBC iD