Newton's Third Law
CONCEPTUALState and apply Newton's Third Law: every force has an equal and opposite reaction force acting on a different object, distinguishing action-reaction pairs from balanced forces
Mastery Evidence
- States Newton's Third Law correctly, identifying both the action and reaction force and the objects they act on
- Gives at least two real-world examples (e.g. rocket propulsion, swimmer pushing off a wall)
- Distinguishes a Newton's Third Law pair from balanced forces on the same object
- Explains why a gun recoils when fired using Newton's Third Law
Assessment Prompt
“If [child] saw a video of a rocket launching into space, could they explain what force is pushing the rocket upward and where that force comes from — and which law of motion that demonstrates?”
Curriculum Standards2 alignments
MS-PS2-1Next Generation Science Standards (NGSS) Middle Schoolcodes onlyKS3.Sci.Phys.MotionAndForces.7The national curriculum in Englandforces and Newton's Laws: Newton's First Law; forces and acceleration (Newton's Second Law); Newton's Third Law
Prerequisites1
- Newton's First & Second LawshardAges 12—13
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- Newton's First & Second Laws hard
Newton's Third Law is conventionally taught after the first two — students need Newton's 1st and 2nd as reference points to distinguish reaction pairs from balanced forces
- Resultant Forces hard
Newton's 1st and 2nd laws are defined in terms of resultant force — the concept of balanced and unbalanced forces must be understood first
- Pushes & Pulls hard
KS3 forces as vectors extends KS2 introduction to pushes and pulls changing speed and direction
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Force & Motion Vocabulary hard
Describing balanced and unbalanced forces as vector quantities requires resultant force, balanced forces vocabulary
- Drawing Force Diagrams hard
Forces as vectors with magnitude and direction is the formal underpinning of the force arrow representation
- Contact & Non-Contact Forces hard
KS3 resultant force and balanced forces extends KS2 distinction between contact and non-contact forces
- Drawing Force Diagrams soft
Distinguishing contact and non-contact forces is clarified by drawing force diagrams showing where arrows originate
- Friction & Surfaces hard
Must experience contact forces like friction before distinguishing contact vs non-contact forces
- Pushes & Pulls hard
Must understand forces change motion before comparing movement on different surfaces
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Mass vs Weight soft
Gravity (weight = mg) is the main worked example for Newton's laws — mass/weight distinction gives concrete numbers for F = ma
- Gravity & Falling Objects hard
KS3 weight = mass × g extends KS2 introduction to gravity as the force pulling objects toward Earth
- Balanced & Unbalanced Forces soft
Balanced/unbalanced forces supports understanding gravity as an unbalanced force on unsupported objects
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Drawing Force Diagrams hard
Investigating balanced and unbalanced forces requires drawing force diagrams to record and analyse experimental findings
- Friction & Surfaces hard
Must understand friction affects motion before investigating balanced/unbalanced forces
- Pushes & Pulls hard
Must understand forces change motion before comparing movement on different surfaces
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Forces Vocabulary hard
Explaining gravity requires the force vocabulary: gravity, weight, non-contact force
- Drawing Force Diagrams hard
Explaining gravity as a downward force requires representing it as a downward arrow in a force diagram
- Contact & Non-Contact Forces hard
Must know about non-contact forces before learning gravity as a non-contact force
- Drawing Force Diagrams soft
Distinguishing contact and non-contact forces is clarified by drawing force diagrams showing where arrows originate
- Friction & Surfaces hard
Must experience contact forces like friction before distinguishing contact vs non-contact forces
- Pushes & Pulls hard
Must understand forces change motion before comparing movement on different surfaces
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Air Resistance & Friction soft
Newton's laws explain why friction and air resistance slow objects down — the KS2 observation of resistance now has a theoretical explanation
- Gravity & Falling Objects soft
Understanding gravity helps contextualise resistive forces opposing gravitational motion
- Balanced & Unbalanced Forces soft
Balanced/unbalanced forces supports understanding gravity as an unbalanced force on unsupported objects
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Drawing Force Diagrams hard
Investigating balanced and unbalanced forces requires drawing force diagrams to record and analyse experimental findings
- Friction & Surfaces hard
Must understand friction affects motion before investigating balanced/unbalanced forces
- Pushes & Pulls hard
Must understand forces change motion before comparing movement on different surfaces
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Forces Vocabulary hard
Explaining gravity requires the force vocabulary: gravity, weight, non-contact force
- Drawing Force Diagrams hard
Explaining gravity as a downward force requires representing it as a downward arrow in a force diagram
- Contact & Non-Contact Forces hard
Must know about non-contact forces before learning gravity as a non-contact force
- Drawing Force Diagrams soft
Distinguishing contact and non-contact forces is clarified by drawing force diagrams showing where arrows originate
- Friction & Surfaces hard
Must experience contact forces like friction before distinguishing contact vs non-contact forces
- Pushes & Pulls hard
Must understand forces change motion before comparing movement on different surfaces
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
- Forces Vocabulary hard
Identifying air resistance, water resistance, and friction requires these force terms
- Drawing Force Diagrams hard
Identifying and explaining air resistance and friction requires drawing force arrows to show opposing forces
- Friction & Surfaces hard
Must know friction from surface comparisons before learning about air/water resistance as similar forces
- Pushes & Pulls hard
Must understand forces change motion before comparing movement on different surfaces
- Drawing Force Diagrams soft
Understanding pushes and pulls as forces is supported by the arrow representation of magnitude and direction
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