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Chapter 3

Newton’s Law. Chapter 3. Newton’s Laws. Newton’s First Law Law of Inertia Newton’s Second Law F = m a Newton’s Third Law Action Reaction Law of Universal Gravitation. Mass. …is measured in kilograms . …is the measure of the inertia of an object.

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Chapter 3

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  1. Newton’s Law Chapter 3

  2. Newton’s Laws • Newton’s First Law • Law of Inertia • Newton’s Second Law • F = ma • Newton’s Third Law • Action Reaction • Law of Universal Gravitation

  3. Mass • …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.

  4. Force • …the agency of change. • …changes the velocity. • …is a vector quantity. • ...measured in Newton’s.

  5. Ancient View of the Cosmos • Universe is 2-D • All celestial objects attached to a sphere. • Celestial Sphere is close • Climb a high mountain and touch the sky • Celestial objects are self-luminous • Earth is the center of the universe • Objects move on perfectcircles

  6. Aristotelian UniverseTerrestrial Realm • Composition predicts motion natural tendencies Fire and Air tend to rise Earth and Water tend to sink • Overall tendency to seek rest • Objects following tendencies require no force • Objects are corruptible (changing)

  7. Aristotelian UniverseCelestial Realm • Celestial Objects composed of Aether Self luminous but does not consume • Motion is constant,circular • Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere

  8. 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.”

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

  10. Newton’s Second Law The Sum of theForcesacting on a body is proportional to the acceleration that the body experiences • F a • SF = (mass) a

  11. Net Force

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

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

  14. 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?

  15. 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?

  16. Weight • The weight of an object FW is the gravitational force acting downward on the object. • FW = m g

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

  18. 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

  19. Coefficient of Friction • Kinetic Friction • Ff = mk FN • Static Friction • Ff ms FN • In most cases, mk < ms.

  20. On to problems...

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