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Big Picture — Force and Motion
Force decides Motion
Look at the net force
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Net force = 0
Object stays at rest or moves at constant velocity (first law).
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Net force ≠ 0
Object accelerates, F = ma (second law).
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Every force has an equal, opposite partner (third law)
Mind Map of the Chapter
Force of friction
Acts opposite to the direction of motion.
Newton's first law
An object stays at rest or in constant-velocity motion unless a net force acts.
Newton's second law
Acceleration is along the net force, proportional to it and inversely to mass (F = ma).
Newton's third law
Every action has an equal and opposite reaction on a different object.
System of objects
Connected objects can be treated as one; only external forces matter.
Key Terms
- Force
- A push or pull with magnitude and direction; SI unit newton (N).
- Weight
- The gravitational force with which the Earth pulls an object.
- Balanced forces
- Equal and opposite forces giving zero net force.
- Net force
- The combined effect of all forces on an object.
- Force of friction
- A force opposing motion between surfaces in contact.
- Normal force
- The upward push of a surface, perpendicular to it.
- Inertia
- The tendency to resist a change in the state of motion.
- Newton's first law
- No net force means no change in motion.
- Newton's second law
- F = ma; acceleration is along the net force.
- Acceleration due to gravity (g)
- 9.8 m s −2 near the Earth.
- Newton's third law
- Equal and opposite forces on two different objects.
- System of objects
- Connected objects treated as one whole.
