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Newton’s Laws of Motion I. Law of Inertia II. F=ma III. Action-Reaction.

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Presentation on theme: "Newton’s Laws of Motion I. Law of Inertia II. F=ma III. Action-Reaction."— Presentation transcript:

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2 Newton’s Laws of Motion I. Law of Inertia II. F=ma III. Action-Reaction

3 Demo: table cloth trick Draw the apparatus Draw the apparatus What do you predict will happen? What do you predict will happen? Record what does happen Record what does happen Why do you think this happened? Why do you think this happened? Demo: eggs in beakers Draw the apparatus Draw the apparatus What do you predict will happen? What do you predict will happen? Record what does happen Record what does happen Why do you think this happened? Why do you think this happened? p32

4 While most people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean).

5 Newton’s Laws of Motion 1 st Law – An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. 1 st Law – An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. 2 nd Law – Force equals mass times acceleration. 2 nd Law – Force equals mass times acceleration. 3 rd Law – For every action there is an equal and opposite reaction. 3 rd Law – For every action there is an equal and opposite reaction.

6 1 st Law of Motion (Law of Inertia) An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. Examples: tablecloth trick tablecloth table cloth trick mythbusters style cloth

7 Compare Video 1 Video 1 1.) What factors determine the “success” of the tablecloth trick? 2.) What physics vocab do they use? 3.) Did increasing the mass make the dishes move more or less? Video 2 Video 2 1.) What two forces did Adam say must be balanced? 2.) What did they change to try and balance these forces?

8 1 st Law Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. These pumpkins will not move unless acted on by an unbalanced force.

9 Explain why the glassware stayed on the table and the eggs fell into the beakers (using the words inertia and friction)

10 1 st Law Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop! Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

11 1 st Law Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever. Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

12 Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? It’s a force we sometimes cannot see – friction.

13 Objects on earth, unlike the frictionless space the moon travels through, are under the influence of friction.

14 There are four main types of friction: There are four main types of friction: Sliding friction: Sliding friction: ice skating Rolling friction: Rolling friction: bowling Fluid friction (air or liquid): Fluid friction (air or liquid): air or water resistance Static friction: Static friction: initial friction when moving an object What is this unbalanced force that acts on an object in motion?

15 Slide a book across a table and watch it slide to a rest position. The book comes to a rest because of the presence of a force - that force being the force of friction - which brings the book to a rest position.

16 In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.) In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.)

17 Newtons’s 1 st Law and You Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

18 Newton’s First Law: A Running Start (AP p132) What do you think? What do you think? Investigate...record data and answer questions 1-5 in your notebook. The materials are at the lab benches. Investigate...record data and answer questions 1-5 in your notebook. The materials are at the lab benches. Put the lab materials back in the covered bin and Get a stamp from your teacher when you are finished at the lab station Put the lab materials back in the covered bin and Get a stamp from your teacher when you are finished at the lab station Return to your seats and read p Answer CU p138 (1-6)/ CDP Return to your seats and read p Answer CU p138 (1-6)/ CDP Work on Project Work on Project p34

19 Model for Forces DQ: How do unbalanced forces change the motion of an object? 1.) An object at rest remains at rest 2.) An object in motion remains in motion at a constant speed unless acted upon by a force 3.) Rest is a special case of constant motion in a straight line with a constant speed (v=0) 4.) Inertia is the property of an object to remain at rest or in motion unless something causes it to move. Inertia resists a change in an object’s state of motion. p35

20 Hoop Dreams Play (10 min) Play (10 min) Record Record Draw a picture and describe your technique(s). Show on the diagram where to grab the hoop and the correct direction to move it so that the result is the hex nut falling into the bottle. When you are finished with your picture, raise your hand and show your teacher to get the next page. p33

21 Talk. Take turns. Each partner gets to say one sentence at a time (if there is an adult observing, wait for the words to be recorded before the next person takes a turn). 1.) Why does the hex nut fall into the bottle when the hoop is pulled/pushed? 2.) Why does that technique work while others do not (trust me…there is essentially only one way to make the trick work)

22 Watch XVR4 XVR4 Record the important physics vocab that are used in the video: Write. Now use these words in your answer to the driving question (again): Why does the hex nut fall into the vessel when the hoop is pushed/pulled? You may add a labeled picture to help explain what you mean, but your answer must be in paragraph form…

23 Physics in action  Benchmark 19/3  Benchmark 29/18-9/19  Benchmark 3 9/22-9/26  Benchmark 49/26-10/3  Benchmark 5 10/3-10/17  Benchmark 6 10/17  Benchmark 7 (Presentation time!) 10/21

24 Review CU (p138) 1-6 CU (p138) 1-6 PtoGo (p143) 1-4 (p144) 10 PtoGo (p143) 1-4 (p144) 10 CDO CDO Get your notebook stamped when you are finished. Then work on your project. Get your notebook stamped when you are finished. Then work on your project. p34 p33

25 Model for Forces DQ: How do unbalanced forces change the motion of an object? 5.) a ball should roll forever (once it is set in motion). However, outside forces (friction) cause it to slow down and stop. 6.) In the absence of friction, a ball released from one side of a track should roll to the same height on the other side of the track 7.) Two people, one on a train and the other outside, will measure different speeds for the same moving object. Both are correct for their frame of reference p35

26 2 nd Law p36

27 2 nd Law The net force of an object is equal to the product of its mass and acceleration, or F=ma.

28 Which falls faster, a penny or a feather? Demo Demo Demo Conclusion: Conclusion: In air (and therefore with air resistance called fluid friction) __________ will fall faster In air (and therefore with air resistance called fluid friction) __________ will fall faster In space (no air resistance) In space (no air resistance)_______________________________________

29 Newton’s 2 nd Law proves that different masses accelerate to the earth at the same rate, but with different forces. We know that objects with different masses accelerate to the ground at the same rate. However, because of the 2 nd Law we know that they don’t hit the ground with the same force. F = ma 98 N = 10 kg x 9.8 m/s/s F = ma 9.8 N = 1 kg x 9.8 m/s/s

30 2 nd Law When mass is in kilograms (kg) and acceleration is in m/s/s, When mass is in kilograms (kg) and acceleration is in m/s/s, the unit of force is in newtons (N). One newton is equal to the force required to accelerate one kilogram of mass at one meter/second/second. One newton is equal to the force required to accelerate one kilogram of mass at one meter/second/second.

31 2 nd Law (F = m x a) How much force is needed to accelerate a 1400 kilogram car 2 meters per second/per second? Write the formula Write the formula F = m x a Fill in given numbers and units Fill in given numbers and units F = 1400 kg x 2 meters per second/second Solve for the unknown Solve for the unknown 2800 kg-meters/second/second or 2800 N

32 If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.

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34 Types of Forces Contact Forces Friction Tension Normal Air resistance Applied Spring Distance Forces Gravitational (weight) Electrical Magnetic

35 Check Your Understanding 1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object? 1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object? 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec? 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?

36 Check Your Understanding 1. What acceleration will result when a 12 N net force applied to a 3 kg object? 1. What acceleration will result when a 12 N net force applied to a 3 kg object? 12 N = 3 kg x 4 m/s/s 12 N = 3 kg x 4 m/s/s 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. 16 N = 3.2 kg x 5 m/s/s 16 N = 3.2 kg x 5 m/s/s 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 66 kg-m/sec/sec or 66 N 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec? 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec? 9800 kg-m/sec/sec or 9800 N 9800 kg-m/sec/sec or 9800 N

37 Gravitational Force (Weight) Weight (a force) is caused by gravity (acceleration) pulling you (your mass) towards the earth Weight (a force) is caused by gravity (acceleration) pulling you (your mass) towards the earth Using Newton’s 2 nd Law F=ma where force is your weight in newtons, mass must be in kg (not pounds), and gravity is 9.8 m/s 2 (round off…g=10 m/s 2 ) Using Newton’s 2 nd Law F=ma where force is your weight in newtons, mass must be in kg (not pounds), and gravity is 9.8 m/s 2 (round off…g=10 m/s 2 ) Weight= mass x gravityW=mg Weight= mass x gravityW=mg

38 Weight depends on gravity Gravity on earth is 9.81 m/s2 Gravity on earth is 9.81 m/s2 What is your weight on earth if your mass is 50 kg? What is your weight on earth if your mass is 50 kg? W=mg W=mg Gravity on the moon is m/s2 Gravity on the moon is m/s2 What is your weight on the moon if your mass is 50 kg? What is your weight on the moon if your mass is 50 kg? W=mg W=mg Your mass remains the same, but your weight is different on the earth than on the moon because there is more gravity on earth

39 Finish CU (p138) 1-6 CU (p138) 1-6 PtoGo (p143) 1-4 (p144) 10 PtoGo (p143) 1-4 (p144) 10 CDP 3-1 CDP 3-1 Get your work stamped before you go Get your work stamped before you go p34 p37

40 Newton’s 2 nd Law: Push or Pull (AP p ) What do you think? What do you think? Investigate...record data and answer questions 1-9 in your notebook. The materials are at the lab benches. Investigate...record data and answer questions 1-9 in your notebook. The materials are at the lab benches. Put the lab materials back in the covered bin and Get a stamp from your teacher when you are finished at the lab station Put the lab materials back in the covered bin and Get a stamp from your teacher when you are finished at the lab station Return to your seats and read p Answer CU p167 (1-4) Return to your seats and read p Answer CU p167 (1-4) p38 p39

41 Model for Forces DQ: How do unbalanced forces change the motion of an object? 8.) Forces are pushes or pulls. Forces add together to give the net force. 9.) Forces add together as vectors (parallelagram rule) 10.) The total net force on an object is related to its mass and acceleration by Newton’s 2 nd Law F=ma 11.) Weight is the force due to gravity (weight is proportional to mass) W=mg (on earth g=9.81≈10) p35

42 Homecoming! Quiz Monday! FinishCU (p167) 1-4 FinishCU (p167) 1-4 PtoGo (p ) 1-8 Get your work stamped Project time today and tomorrow. Finish Benchmark 4 and begin Benchmark 5. If your partners will not be here Friday make sure you assign them a task to complete over the weekend! Project time today and tomorrow. Finish Benchmark 4 and begin Benchmark 5. If your partners will not be here Friday make sure you assign them a task to complete over the weekend! Warning! Pages should be finished Warning! Pages should be finished p34 p39

43 PtoGo (p ) 1-8 Answers 1.) 2.a) the long jump and shot put involve free- falling objects; therefore the acceleration is due to gravity (g=10 m/s 2 ) b) the negative sign shows that the force and acceleration are in opposite directions F =ma 350 N70 kg5 m/s 2 800N80 kg10 m/s 2 70 N7 kg10 m/s N80 kg5 m/s N100 kg-15 m/s N100 kg-30 m/s 2 p39

44 3.) 42/0.30= 140 m/s2 4.) F=ma=(0.040)(20)= 0.8 N 5.a) A bowling ball has greater inertia (mass) than a baseball therefore a bowling ball has a greater tendency to stay at rest or in motion b) More force is required to make a bowling ball accelerate b) More force is required to make a bowling ball accelerate 6.) F=ma=(0.1)(10)= 1 N thus a “newtonburger” 7.a) if you weigh 150 lbs/2.2 = 68 kg b) F=ma=(68)(10) = 680 N b) F=ma=(68)(10) = 680 N

45 3 rd Law For every action, there is an equal and opposite reaction. For every action, there is an equal and opposite reaction. p35

46 3 rd Law According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

47 3 rd Law There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.

48 Free Body Diagrams Use arrows (vectors) to show all the forces acting on an object Use arrows (vectors) to show all the forces acting on an object The size of the arrow represents the strength of each force The size of the arrow represents the strength of each force The direction of the arrow is the direction of the force The direction of the arrow is the direction of the force

49 Draw the free-body diagram for this person What forces are at work? What forces are at work? What is the sum of these forces? What is the sum of these forces?

50 What is the sum of the forces?

51 Newton’s 3 rd Law: Run and Jump (AP p ) Part A (together) Part A (together) Part B (optional) Part B (optional) Finish: CU (p205) 1-3 PtoGo (p208) #8 only CDP 7-2 p35

52 Model for Forces DQ: How do unbalanced forces change the motion of an object? 12.) Forces come from interactions between objects. This means that forces come in pairs. 13.) For each pair of forces, the forces are equal, but in opposite directions (Newton’s 3 rd Law) p35

53 Newton’s 3rd Law in Nature Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).

54 3 rd Law Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

55 Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). Action-reaction force pairs make it possible for birds to fly. Action-reaction force pairs make it possible for birds to fly.

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57 Other examples of Newton’s Third Law The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction). The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

58 3 rd Law Consider the motion of a car on the way to school. A car is equipped with wheels which spin backwards. As the wheels spin backwards, they grip the road and push the road backwards. Consider the motion of a car on the way to school. A car is equipped with wheels which spin backwards. As the wheels spin backwards, they grip the road and push the road backwards.

59 3 rd Law The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction.


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