N e w t o n’ s L a w s Unit 3

3.1 Force and Mass

3.1 Force and mass Force – push or pull Vector – so magnitude and direction Example of Contact Forces Friction Tension Applied Spring Examples of Field Forces Gravitational Electric Magnetic

3.1 Force and mass Mass – measurement of how difficult it is to change the objects velocity Inertia – resistance to change in velocity

3.2 Newton’s First Law of Motion

1 st Law An object at rest remains at rest as long as no net force acts on it. An object moving with constant velocity continues to move with the same speed and in the same direction as long as not net force acts on it.

3.2 Newton’s First Law of Motion Sometimes called the Law of Inertia

3.3 Newton’s Second Law of Motion

2 nd Law A net force causes an acceleration in the direction of the net force. Simulation

3.3 Newton’s Second Law of Motion Free body diagrams Show all the forces acting on an object For example an object sitting on a table W – weight = mg N – Normal Force (perpendicular) to the surface N W

3.3 Newton’s Second Law of Motion Free body diagrams If a rope pulls the object toward the right, then T = Tension N W T Practice Free Body

3.3 Newton’s Second Law of Motion Free body diagrams Steps in problems solving 1.Sketch the forces 2.Isolate the Object 3.Choose a Coordinate System 4.Resolve the Forces into Components 5.Apply Newton’s Second Law of Motion

3.3 Newton’s Second Law of Motion A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30 o to the horizontal. What is his acceleration?

3.3 Newton’s Second Law of Motion A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30 o to the horizontal. What is his acceleration? Free Body diagram

3.3 Newton’s Second Law of Motion A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30 o to the horizontal. What is his acceleration? Free Body diagram N W T

3.3 Newton’s Second Law of Motion A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30 o to the horizontal. What is his acceleration? Free Body diagram Axis N W T

3.3 Newton’s Second Law of Motion A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30 o to the horizontal. What is his acceleration? Free Body diagram Axis N W T TyTy TxTx

3.3 Newton’s Second Law of Motion A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30 o to the horizontal. What is his acceleration? Free Body diagram Axis Equation N W TyTy TxTx

3.4 Newton’s Third Law of Motion

For every force that acts on an object, there is a reaction force acting on a different object that is equal in magnitude and opposite in direction. If object 1 exerts a force F on object 2, then object 2 exerts a force –F on object 1.

3.4 Newton’s Third Law of Motion What are the action reaction pairs in the following?

3.4 Newton’s Third Law of Motion A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg. A.What is the acceleration of the man? B. What is the acceleration of the canoe?

3.4 Newton’s Third Law of Motion A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg. Free Body Diagrams P NcNc WcWc P WmWm NmNm

3.4 Newton’s Third Law of Motion A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg. Equations P NcNc WcWc P WmWm NmNm

3.4 Newton’s Third Law of Motion A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg. A-acceleration of man P NcNc WcWc P WmWm NmNm

3.4 Newton’s Third Law of Motion A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg. A – acceleration of canoe P NcNc WcWc P WmWm NmNm

3.4 Newton’s Third Law of Motion Two boxes are tied together with a rope, and the first one is pulled by a second rope. Both boxes accelerate at 2.0 m/s 2. If the front box has a mass of 25 kg, and the second a mass of 50 kg, what is the tension on each rope? a

3.4 Newton’s Third Law of Motion Free body diagrams NfNf WfWf T1T1 T2T2 WbWb NbNb T2T2

3.4 Newton’s Third Law of Motion Equations Solve (add) NfNf WfWf T1T1 T2T2 WbWb NbNb T2T2

3.5 The Vector Nature of Forces

Forces are vectors, so they can be treated using vectors rules

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Free Body Diagram? W L B

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Components? W L BByBy BxBx

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Components? W L ByBy BxBx LyLy LxLx

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Equations? W ByBy BxBx LyLy LxLx

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Values? W ByBy BxBx LyLy LxLx

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Values? W ByBy BxBx LyLy LxLx

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Solve? W ByBy BxBx LyLy LxLx

3.5 The Vector Nature of Forces Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 28 o. What is the angle of Bob’s force? Solve? W ByBy BxBx LyLy LxLx

3.6 Frictional Forces

Friction – force that opposes motion Caused by microscopic irregularities of a surface Increases as pushing force increases

3.6 Frictional Forces Depends on the normal force and the type of surface f – force of friction (N) N – normal force  – coefficient of friction (1 or less)

3.6 Frictional Forces Three types of friction 1.Static – object at rest 2.Kinetic – object in motion 3.Rolling – just like it sounds Surfacesµ (static)µ (kinetic) Steel on steel Glass on glass Metal on Metal (lubricated) Ice on ice Teflon on Teflon0.04 Tire on concrete10.8 Tire on wet road Tire on snow0.30.2

3.6 Frictional Forces Example