Download Newton*s Third Law

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.
• 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)