1. Newton’s Laws of Motion

2. Newton’s Laws Newton’s First Law Newton’s Second Law
Law of Inertia
Newton’s Second Law
Newton’s Third Law
Law of Action and Reaction
Law of Universal Gravitation

3. Mass …is the amount of “stuff” in an object.
…is measured in kilograms.
…is the measure of the inertia of an object.
Inertia is the natural tendency of a body resist changes in motion.

7. History of Inertia
Aristotle ( BCE): “…a constant force will yield a constant speed.”
Jean Buridan ( ): believed that objects stayed in motion because they possessed “impetus” – something inside that makes them continue to move.
Galileo Galilei ( ): challenged the commonly held belief that an object’s motion was the result of continued force. Instead, he viewed uniform motion as being a state just as natural as rest.
OK!

8. Galileo’s Thought Experiments on Motion
Ball drop from leaning tower of Pisa
Galileo’s Inclined Planes

9. Force …is a push or pull that changes the velocity of an object.
…is a vector quantity.
...measured in Newtons.

10. Newton’s First Law Law of Inertia
“A body remains at rest or moves in a straight line at a constant speed unless acted upon by a force.”
The more massive the object, the greater the tendency to keep doing what it is already doing.

11. Newton’s First Law No mention of chemical composition
No mention of terrestrial or celestial realms
Net force required when object changes motion
Acceleration is the observable consequence of forces acting

12. Newton’s Second Law F  a S F = (mass) a
The Sum of the Forces acting on a body is proportional to the acceleration that the body experiences
F  a
S F = (mass) a

13. Net Force

14. Newton’s Third Law Action-Reaction
For every action force there is an equal and opposite reaction force

15. The Law of Gravity G = 6.67  10-11 N·m2/kg2
Every mass exerts a force of attraction on every other mass.
The math…
G = 6.67  N·m2/kg2

16. Gravity Questions
Did the Moon exert a gravitational force on the Apollo astronauts?
What kind of objects can exert a gravitational force on other objects?

17. Gravity Questions
The constant G is a rather small number. What kind of objects can exert strong gravitational forces?
If the distance between two objects in space is doubled, then what happens to the gravitational force between them?

18. Weight
The weight of an object Fg is the gravitational force acting downward on the object.
Fg = m g

19. Tension (Tensile Force)
Tension is the force in a string, chain or tendon that is applied tending to stretch it. FT

20. Normal Force
The normal force on an object that is being supported by a surface is the component of the supporting force that is perpendicular to the surface. FN

21. Coefficient of Friction
Kinetic Friction
Ff = mkFN
Static Friction
Ff  msFN
In most cases, mk < ms.

22. On to problems...