Newton's Third Law and Conservation of Momentum
Forces occur in equal and opposite pairs acting on different bodies; consequently the total momentum of an isolated system is conserved.
What is Newton's Third Law and Conservation of Momentum?
Forces occur in equal and opposite pairs acting on different bodies; consequently the total momentum of an isolated system is conserved.
Key formula / rule: Action and reaction act on different bodies and are of the same type.
Key points
- State the third law and identify the correct force pair in a situation.
- Apply momentum conservation to recoil and explosion problems.
Common exam trap
Cancelling action-reaction pairs within the same free-body diagram.
Definitions
- Term
Newton's Third Law and Conservation of Momentum
- Meaning
Forces occur in equal and opposite pairs acting on different bodies; consequently the total momentum of an isolated system is conserved.
- Term
Newton's Third Law and Conservation of Momentum — explanation
- Meaning
The pair members never act on the same body, which is why they never cancel in a free-body diagram of one body. Momentum conservation follows directly and is the tool of choice for collisions and explosions.
Learning objectives
State the third law and identify the correct force pair in a situation.
Apply momentum conservation to recoil and explosion problems.
Formulae
- Key point
Action and reaction act on different bodies and are of the same type.
- Key point
Total momentum is conserved when the net external force is zero.
- Key point
Internal forces cannot change the momentum of a system.
Prerequisites
PHY-U1-NLM-T1-S1-C2
Common mistakes
Cancelling action-reaction pairs within the same free-body diagram.
Applying momentum conservation when a significant external force acts.
Keywords
Newton
Third
Conservation
Momentum
Practice preview
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