Newton’s Laws of Motion

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Newton’s Laws of Motion. History. Aristotle First to study motion Galileo Dropped big and small rock  Fell at same rate If no interference – motion will go on forever. History. Newton formalized ideas At 23 (1665) he overthrew Aristotle’s 2000 year old ideas LAWS OF MOTION. Key Terms. - PowerPoint PPT Presentation

Text of Newton’s Laws of Motion

  • AristotleFirst to study motion

    GalileoDropped big and small rock Fell at same rateIf no interference motion will go on forever

  • Newton formalized ideasAt 23 (1665) he overthrew Aristotles 2000 year old ideas LAWS OF MOTION

  • ForceThe cause of an acceleration (or the change in an objects motion) Force = mass x accelerationUnits:Newton SI Unit of Force (kg x m/s2)Dyne CGS Unit of Force (g x cm/s2)Pound English Unit of Force (slug x ft/s2)

  • Inertia The tendency of an object to maintain its state of motionEquilibriumThe state of a body in which there is no change in its motionWeightThe magnitude of the force of gravity acting on an objectWeight = mass x acceleration

  • Law of Inertia

    An object continues in its state of rest, or of uniform motion in a straight line, unless it is acted upon by an unbalanced force

    Object any body

    Continues keeps rest or moving

    Unbalanced force net force, not in equilibrium

  • Why Law of Inertia?Tendency of a body to resist change of motionMore matter = more inertiaEx. If chased by an elephant, how should you run away? Zigzag!!

  • Wood


    Cardboard Same volumes take up the same amount of space Which is harder to move? More inertia More mass (mass is a measure of inertia)VVVIIIMMM

  • Does mass = weight?Mass quantity of matter in a bodyWeight measure of gravitational force which acts on a body W = mgDepends on where the object isEx. Earth, Moon, Spaceg = 9.8 m/s2 g = 1.6 m/s2 g = ?

  • Gravity on the Moon Gravity around the Solar System

  • How much would a 75 kg (165 lb) person weigh on the Moon? On Mars?gmoon= 1.62 m/s2gmars= 3.77 m/s22.2 pound = 1 kilograms1 pound = 4.45 Newtons

    Moon: 121.5 N or 27.3 lbsMars: 282.8 N or 63.5 lbs

  • On bus (rest rest)Standing and bus moves forwardYou seem to fall backwardActually feet move forward with bus and body remains at restBus stops?

  • Dishes on Table (rest rest)Snap a cloth from beneathFriction between dishes and cloth not enough to move dishes

  • In stopping car (motion motion)Fly forwardKeep moving while car stops

  • Deals with accelerationAcceleration = a = v / tEx. Car died tow 5 N50 NWhich provides the greater acceleration?Which can get car from 0 mi/hr to 20 mi/hr faster?GREATER FORCE

  • With same force, which can go from 0 mi/hr to 50 mi/hr faster?Mass = 1000 kg


  • Force = mass x acceleration (F = ma)

    The more force on an object, the more it accelerates. The more massive an object, the more it resists acceleration.

  • The acceleration of a body is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the body* in the same direction as the net forcea in the same direction of bodys motion speed upa in opposite direction of bodys motion slow downa at right angles to direction of bodys motion deflect circularAny other change in speed and direction

  • mkgsNewtons (N)(kg x m/s2) cmgsDyne (g x cm/s2)

    ftslugssPounds (lbs)(slugs x ft/s2)


    mkscgsEnglish LengthMassTimeVelocityAccelerationForce

  • Weight = W = g = Use ______________ as force unitsA force is a __________ or a __________ Now also say: Force is anything that can ____________ a body.mass x gravityN or lbs-9.8 m/s2 or -32 ft/s2N or lbspush pullaccelerate

  • Galileo gave no reason why bodies fall with an acceleration.Newton did.Newton a F pulls on a body and pulls it toward the Earth.F = maHeavier body attracted with more F.Heavier body has more m andMore IMore resistance to changeEx. If 2 x F and 2 x m same net acceleration

  • Force:Causes accelerationA push or a pullAlways involves two objects interactionEx. Hammer and NailHammer exerts force on nailIn process, nail slows down hammerTherefore, nail exerts force on hammerEx. Ice skater with rifle or with mitt

  • To every action there is an equal and opposite reactionOne force is action force, other is reactionNeither can exist without the otherActionWeightlifter lifts on barbellFeet down on EarthYou sit on chairTires sit on roadYou push on wallHelical blades push down on particlesRifle pushes bulletReactionBarbell pulls on weightlifterEarth pushes up on feetChair pushes up on youRoad pushes up on tiresWall pushes back on youParticles push up on bladesBullet pushes back on rifle (KICK)SAME FORCE: F/mb = aF/mr = a

  • Sometimes not so obvious.Reactions in free-fallEarth pulls on body = actionBody pulls on Earth = reactionTherefore, can say boulder falls to Earth or Earth falls to boulderF is equal but acceleration is very smallWhen step off curb street comes up to meet youBug against windshield deceleration of car small, deceleration of bug large

  • When objects are relatively the same mass, both forces are more easily noticed since both accelerations are about equal.