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Newton’s Third Law. Newton’s Laws of Motion. Newton’s first law: NL1 - A body will remain at rest or will continue to move with a constant velocity unless external forces cause it to do otherwise.
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Newton’s Laws of Motion • Newton’s first law: NL1- A body will remain at rest or will continue to move with a constant velocity unless external forces cause it to do otherwise. • Newton’s second law: NL2- The acceleration produced by a resultant applied force is proportional to the mass of the body on which it acts. • Newton’s third law: NL3- Whenever two bodies interact, they exert forces on each other which are equal in magnitude and opposite in direction.
Newton’s Laws of Motion • Newton’s first law: NL1- Resultant force causes change in speed or direction of motion. • Newton’s second law: NL2- F = ma • Newton’s third law: NL3- Equal and opposite forces.
Equilibrium • Students confuse equilibrium from NL1 with pairs of forces from NL3. • Equilibrium occurs when the resultant force on a body is zero. • Sometimes (but not always) this is due to a pair of equal and opposite forces acting on the same body, e.g. weight and normal reaction force. • Pairs of forces from NL3 do not act on the same body
Mechanics in Action • Chapter Four: Misconceptions, p.44 (p.50) • Chapter Five: Practical Investigations • Bathroom Scales and a Broom, p.61 (p.67) • Worksheets, after p. 166 (p. 173)