Newton’s I And II Laws Of Motion - Weebly

Newton’s I and II Laws of Motion

What will happen if You apply the same force F to the following objects?Sumo WrestlerSmurfThe Smurf will experience a greater acceleration than theSumo Wrestler!

What Have We Learned?The force applied to an object is proportional to its acceleration.Object 1 1.0 kgObject 2 2.0 kgObject 3 3.0 kgOn your whiteboard, draw a force-acceleration graph for allthree objects on the same axes!

What Have We Learned?When there is a bigger mass, more force is needed to get thesame acceleration.Object 1 1.0 kgObject 2 2.0 kgObject 3 3.0 kgThe mass determines how steep the line is on your graph!

What’s the Mathematical Model?y mxFapplied maNewton Kg m/s21 N 0.225 lbsThis is very similar to Newton’s II Law!The acceleration of an object as produced by a net forceis directly proportional to the magnitude of the net forceand in the same direction as the net force, while it isinversely proportional to the mass of the object.

What’s a Net Force?Objects often experience multiple forces.Person APerson BFA 25 NFB 40 NFnetx FA FBaFBFnetFnet ΣFxFAΣFx Vector sum

What’s an Unbalanced Force?Objects often experience multiple forces.Person APerson BFA 25 NFB 40 NFnetx maxaFA FB maxFBFnetm 1.0 kgFAax (FA FB)/max (-25 N 40 N)/1 kg -15 m/s2

What Do We Do Now?FCFA 25 NFB 40 NFBaxFDFC 20 NFAFD 10 NFnetyayFnetxFnetx maxFnety mayFA FB maxFC FD mayax -15 m/s2ay 10 m/s2

Put Them Together!FnetyFnetyFnetxFnetxar2 ax2 ay2tan θ ay/axar 18.0 m/s2θ 146

What if the net force is zero?On your whiteboard, create 2 situations that wouldhave a net force of zero!What are the objects acceleration in thesescenarios?Fnet 0Fnet maa 0 m/s2Describe how the objects are moving!

What if the net force is zero?If an object has an accelerationof zero, the object is either:Not MovingMoving at constant velocityMeet Newton’s First Law!Every object persists in its stateof rest or uniform motion in astraight line unless it iscompelled to change that state byforces impressed on it.

Defining BoundariesNewton developed three laws of motion that are able to explainmany different observable phenomena in a simple way.Just like all scientific theories, Newton’s laws operate undera set of assumptions.1.The objects that these laws are being applied toare large compared to the diameter of an atom.At this level, motion is governed by quantum mechanic theory.

Defining Boundaries2.Objects are moving significantly slower than thespeed of light.Object must stay at around 20% of the speed oflight or slower!At higher speeds, motion is governed by the theory of relativity.

Defining Boundaries3.Observations must be made in an inertialreference frame.A reference frame is defined as aset of coordinates that can beused to determine positions andvelocities of objects.According to the person on the train, the velocity of thebox is 0 m/s.According to the person at the train station, the velocityof the box is v m/s.

Reference FramesLet’s say that the personon the train, tosses a ballinto the air.On your whiteboard, draw what the motion of the ball will looklike to a the person on the train and the person on the ground.

Reference FramesAn inertial reference frame is one that is notaccelerating.PhysicsObserve one of the physics books sitting on myfront table.Are you observing it from an inertial referenceframe?Are you moving?

Earth as a Reference FrameTechnically, the Earth’s surface is not an inertialreference frame.The Earth’s rotation andprecession cause us toaccelerate.So why do Newton’s lawswork so well?Because the objects we are observing are so small comparedto the Earth, the effects of the acceleration is so small thatwe can assume that we are in an inertial reference frame.

Dynamics Problem SetTopicNewton’s First and Second LawNewton’s Third LawTypes of ForcesFrictionApplications of Newton’s LawsSectionsQuestions4.3 & 4.41, 3, 10, 12, 144.5164.7 & 4.822, 38, 40, 434.946, 484.10 & 4.1154, 55, 62, 74, 79

How-To-Guide for Free-body Diagrams!1. Draw all vectors starting at the dot.T2. The only vectors that are drawn on the object areFORCES acting on the object.aFg3. Make sure that all forces are labeled appropriately.Fg Force of Gravityfs static frictionN Normal ForceT Tensionfk kinetic friction4. Indicate the magnitude of the force using the length of the vectors.5. Indicate the acceleration of the object using an accelerationvector that is near the object.

What is the process?Choose one of Newton’s LawsFnet 0TFgFnet maApply the law you selectedaFnet maT (-Fg) m(-a)Solve for the appropriate quantity!T - Fg -maT Fg - ma

What is the Force due to Gravity?Choose one of Newton’s LawsFnet 0Fnet maApply the law you selectedaFnet ma-Fg m(-a)FgSolve for the appropriate quantity!Fg magwhere ag 9.8 m/s2

What’s the Force of Friction and NormalForce?NTpfFcFgx-directiony-directionChoose one of Newton’s LawsChoose one of Newton’s LawsFnet 0Fnet maFnet 0Fnet maApply the law you selectedApply the law you selectedFC Tp (-f) 0N (-Fg) 0f FC Tpf 50 NN FgFg 98 N

What’s the coefficient of frictionNTpfFcFgf μNμ f/Nμ 50 N/98 Nμ 0.51

Calvin and Hobbes Meet NewtonHobbes is pulling Calvin on his sled.Calvin and the sled have a total mass of20 kilograms and Hobbes can pull with aforce of 8.5 N. In addition, there is africtional force that acts in the oppositedirection of Hobbes with a magnitude of2.0 N. What will Calvin’s acceleration be?Let’s Make PIES!FgroundaFHobbes 8.5 NFFriction 2.0 Nm 0.300 kgFfriction 2.0 NFHobbes 8.5 NFgravity

Calvin and Hobbes Meet NewtonFgroundFHobbes 8.5 NFFriction 2.0 NFfriction 2.0 NaFHobbes 8.5 Nm 20 kgFgravityFnetx maxFHobbes (-Ffriction) maxFHobbes - Ffriction maxax (FHobbes - Ffriction)/max 0.325 m/s2Fnety 0ay 0 m/s2

Calvin and Hobbes Meet NewtonWhat if Hobbes pulled at a 45 ?FHobbes 8.5 NFHobbesx 8.5 N cos 45 FHobbesy 8.5 N sin 45 FHobbesx 6.0 NFHobbesy 6.0 NThere is still an acceleration in the x-direction!There is still no acceleration in the y-direction!

Calvin and Hobbes Meet NewtonFHobbesx 6.0 NFfriction 2.0 NFHobbesy 6.0 NaFgroundFHobbesyFHobbesxFfrictionm 20 kgFgravityFnetx maxFHobbesx (-Ffriction) maxFHobbesx - Ffriction maxax (FHobbesx - Ffriction)/max 0.25 m/s2Fnety 0ay 0 m/s2Does this make sense?The sled won’t accelerate as muchin the x-direction because some ofthe force is now in the y-direction.

Calvin and Hobbes Meet Newton Hobbes is pulling Calvin on his sled. Calvin and the sled have a total mass of 20 kilograms and Hobbes can pull with a force of 8.5 N. In addition, there is a frictional force that acts in the opposite direction of Hobbes with a magnitude of 2.0 N. What will Calvin