Presentation on theme: "Newton’s Laws of Motion"— Presentation transcript:
1 Newton’s Laws of Motion I. Law of InertiaII. F=maIII. Action-Reaction
2 p32 Demo: eggs in beakers Demo: table cloth trick Draw the apparatus What do you predict will happen?Record what does happenWhy do you think this happened?Draw the apparatusWhat do you predict will happen?Record what does happenWhy do you think this happened?
3 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).
4 Newton’s Laws of Motion 1st 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.2nd Law – Force equals mass times acceleration.3rd Law – For every action there is an equal and opposite reaction.
5 1st 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 tricktable cloth trick mythbusters style
6 CompareVideo 11.) 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 21.) What two forces did Adam say must be balanced?2.) What did they change to try and balance these forces?
7 1st LawInertia 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.
8 Explain why the glassware stayed on the table and the eggs fell into the beakers (using the words inertia and friction)
9 1st LawOnce airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!
10 1st LawUnless acted upon by an unbalanced force, this golf ball would sit on the tee forever.
11 It’s a force we sometimes cannot see – friction. 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.
12 Objects on earth, unlike the frictionless space the moon travels through, are under the influence of friction.
13 Friction! There are four main types of friction: What is this unbalanced force that acts on an object in motion?Friction!There are four main types of friction:Sliding friction: ice skatingRolling friction: bowlingFluid friction (air or liquid): air or water resistanceStatic friction: initial friction when moving an object
14 Slide a book across a table and watch it slide to a rest position 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.
15 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.)
16 Newtons’s 1st 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.
17 Newton’s First Law: A Running Start (AP p132) What do you think?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 stationReturn to your seats and read p Answer CU p138 (1-6)/ CDPWork on Project
18 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
19 Hoop Dreams p33 Play (10 min) 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.
20 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)
21 Watch http://www.youtube.com/watch?v=uOSBC0SXVR4 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 Review p34 p33 CU (p138) 1-6 PtoGo (p143) 1-4 (p144) 10 CDO 2-1 3-2 Get your notebook stamped when you are finished. Then work on your project.p33
24 Model for Forces DQ: How do unbalanced forces change the motion of an object? p355.) 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
26 2nd LawThe net force of an object is equal to the product of its mass and acceleration, or F=ma.
27 Which falls faster, a penny or a feather? DemoConclusion:In air (and therefore with air resistance called fluid friction) __________ will fall fasterIn space (no air resistance)_______________________________________
28 Newton’s 2nd 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 2nd Law we know that they don’t hit the ground with the same force.F = ma98 N = 10 kg x 9.8 m/s/sF = ma9.8 N = 1 kg x 9.8 m/s/s
29 2nd Law 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.
30 2nd Law (F = m x a)How much force is needed to accelerate a 1400 kilogram car 2 meters per second/per second?Write the formulaF = m x aFill in given numbers and unitsF = 1400 kg x 2 meters per second/secondSolve for the unknown2800 kg-meters/second/second or 2800 N
31 If mass remains constant, doubling the acceleration, doubles the force If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.
33 Types of Forces Contact Forces Distance Forces Friction Tension Normal Air resistanceAppliedSpringDistance ForcesGravitational (weight)ElectricalMagnetic
34 Check Your Understanding 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/s2. Determine the mass.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?
35 Check Your Understanding 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/s2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.16 N = 3.2 kg x 5 m/s/s3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?66 kg-m/sec/sec or 66 N4. 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
36 Gravitational Force (Weight) Weight (a force) is caused by gravity (acceleration) pulling you (your mass) towards the earthUsing Newton’s 2nd Law F=ma where force is your weight in newtons, mass must be in kg (not pounds), and gravity is 9.8 m/s2 (round off…g=10 m/s2)Weight= mass x gravity W=mg
37 Weight depends on gravity Gravity on the moon is m/s2What is your weight on the moon if your mass is 50 kg?W=mgGravity on earth is 9.81 m/s2What is your weight on earth if your mass is 50 kg?W=mgYour mass remains the same, but yourweight is different on the earth than onthe moon because there is more gravityon earth
38 p34 p37 Finish CU (p138) 1-6 PtoGo (p143) 1-4 (p144) 10 CDP 3-1 Get your work stamped before you gop37
39 Newton’s 2nd Law: Push or Pull (AP p157-159) What do you think?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 stationReturn to your seats and read p Answer CU p167 (1-4)p39
40 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 2nd 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
41 Homecoming! Quiz Monday! Finish CU (p167) 1-4PtoGo (p ) 1-8Get your work stampedProject 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 finishedp34p39
42 PtoGo (p ) 1-8 Answersp39F =ma350 N70 kg5 m/s2800N80 kg10 m/s270 N7 kg400 N-1500 N100 kg-15 m/s2-3000 N-30 m/s21.) 2.a) the long jump and shot put involve free-falling objects; therefore the acceleration is due to gravity (g=10 m/s2) b) the negative sign shows that the force and acceleration are in opposite directions
43 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 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
44 For every action, there is an equal and opposite reaction. 3rd Lawp35For every action, there is an equal and opposite reaction.
45 3rd LawAccording 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.
46 3rd LawThere 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.
47 Free Body DiagramsUse arrows (vectors) to show all the forces acting on an objectThe size of the arrow represents the strength of each forceThe direction of the arrow is the direction of the force
48 Draw the free-body diagram for this person What forces are at work?What is the sum of these forces?
50 Newton’s 3rd Law: Run and Jump (AP p198-200) Part A (together)Part B (optional)Finish: CU (p205) 1-3PtoGo (p208) #8 onlyCDP 7-2
51 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 3rd Law)p35
52 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.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).
53 3rd LawFlying 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.
54 Consider the flying motion of birds. A bird flies by use of its wings 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).Action-reaction force pairs make it possible for birds to fly.
56 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).
57 3rd LawConsider 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.
58 3rd LawThe 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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