The Three Laws
Galileo 1564 –1642
• Rolled Cannon Balls Down Inclined
Planes
• Concluded ∆v ~ ∆t
• Noticed that if the plane was level
 ∆v = 0
• Velocity would not change – coast
• Aristotle said it was natural for
things to come to rest.
• Galileo said it was natural for
things to keep moving.
Newton 1642-1727
• Mathematical Genius
• Manic-Depressive
No Social Life
• Invented Calculus
• Three Laws of Motion
• Gravitation, Light
• Universe
• First Law:
Three Laws and Gravity
– An Object in Motion Tends to Continue in Motion
• Second Law:
–
–
–
–
–
Acceleration is proportional to Force
a~F
F = m∙a
Force equals mass times acceleration
newton = kg ∙ m/s2
Prob Set 8B
• Third Law:
– To Every Action, there is an opposite and equal reaction.
(If I push you then you push me.)
• The force of gravity is proportional to your mass
– Fgrav = mg