# Newton’s Laws of Motion

## Presentation on theme: "Newton’s Laws of Motion"— Presentation transcript:

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

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

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).

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.

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 trick table cloth trick mythbusters style

Compare 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 1.) What two forces did Adam say must be balanced? 2.) What did they change to try and balance these forces?

1st Law 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.

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

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

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

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.

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

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 skating Rolling friction: bowling Fluid friction (air or liquid): air or water resistance Static friction: initial friction when moving an object

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.

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.)

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.

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 station Return to your seats and read p Answer CU p138 (1-6)/ CDP Work on Project

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

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.

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)

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…

Physics in action Benchmark 1 9/3 Benchmark 2 9/18-9/19
Benchmark 7 (Presentation time!) 10/21

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

Model for Forces DQ: How do unbalanced forces change the motion of an object?
p35 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

2nd Law p36 F = m x a

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

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

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 = ma 98 N = 10 kg x 9.8 m/s/s F = ma 9.8 N = 1 kg x 9.8 m/s/s

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.

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 formula F = m x a Fill in given numbers and units F = 1400 kg x 2 meters per second/second Solve for the unknown 2800 kg-meters/second/second or 2800 N

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.

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

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?

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 2. 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/s 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?  9800 kg-m/sec/sec or 9800 N

Gravitational Force (Weight)
Weight (a force) is caused by gravity (acceleration) pulling you (your mass) towards the earth Using 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

Weight depends on gravity
Gravity on the moon is m/s2 What is your weight on the moon if your mass is 50 kg? W=mg Gravity on earth is 9.81 m/s2 What is your weight on earth if your mass is 50 kg? 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

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

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 station Return to your seats and read p Answer CU p167 (1-4) p39

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

Homecoming! Quiz Monday!
Finish CU (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! Warning! Pages should be finished p34 p39

PtoGo (p ) 1-8 Answers p39 F = m a 350 N 70 kg 5 m/s2 800N 80 kg 10 m/s2 70 N 7 kg 400 N -1500 N 100 kg -15 m/s2 -3000 N -30 m/s2 1.) 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

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

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

3rd 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.

3rd 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.

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

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

What is the sum of the forces?
3

Newton’s 3rd Law: Run and Jump (AP p198-200)
Part A (together) Part B (optional) Finish: CU (p205) 1-3 PtoGo (p208) #8 only CDP 7-2

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

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).

3rd 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.

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.

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).

3rd 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.

3rd 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.