 # Chapter 3 Newtons Law NEXT Newtons Laws Newtons

• Slides: 20 Chapter 3 Newton’s Law NEXT Newton’s Laws Newton’s First Law u. Law of Inertia F Newton’s Second Law u. F = ma F Newton’s Third Law u. Action Reaction F Law of Universal Gravitation F Mass F …is measured in kilograms. F …is the measure of the inertia of an object. F Inertia is the natural tendency of a body resist changes in motion. Force F …the agency of change. F …changes F …is the velocity. a vector quantity. F. . . measured in Newton’s. Ancient View of the Cosmos F F F 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 perfect circles Aristotelian Universe Terrestrial Realm o Composition predicts motion natural tendencies Fire and Air tend to rise Earth and Water tend to sink o Overall tendency to seek rest o Objects following tendencies require no force o Objects are corruptible (changing) Aristotelian Universe Celestial Realm F Celestial Objects composed of Aether Self luminous but does not consume F F Motion is constant, circular Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere Newton’s First Law F “A of Inertia body remains at rest or moves in a straight line at a constant speed unless acted upon by a force. ” Newton’s First Law F No mention of chemical composition F No mention of terrestrial or celestial realms F Force required when object changes motion F Acceleration is the observable consequence of forces acting Newton’s Second Law The Sum of the Forces acting on a body is proportional to the acceleration that the body experiences SF a S F = (mass) a Net Force Newton’s Third Law F Action-Reaction F For every action force there is an equal and opposite reaction force The Law of Gravity F Every mass exerts a force of attraction on every other mass. F The math… FG = 6. 67 10 -11 N·m 2/kg 2 Gravity Questions F Did the Moon exert a gravitational force on the Apollo astronauts? F What kind of objects can exert a gravitational force on other objects? Gravity Questions F The constant G is a rather small number. What kind of objects can exert strong gravitational forces? F If the distance between two objects in space is doubled, then what happens to the gravitational force between them? Weight F The weight of an object FW is the gravitational force acting downward on the object. F FW = mg Tension (Tensile Force) F Tension is the force in a string, chain or tendon that is applied tending to stretch it. F FT Normal Force F 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. F FN Coefficient of Friction F Kinetic Friction • Ff = mk FN F Static Friction • Ff ms FN F In most cases, mk < ms. On to problems. . .