Chapter 2- Physics In Action

Section 1

Learning Objectives

• Describe Galileo's law of Inertia
• Apply Newton's first law of motion
• Recognize inertial mass as a physical property of matter
• Use examples to demonstrate that speed is always relative to some other object
• Explain that speed of an object depends on the reference frame from which it is being observed

What do you see?

• The mouse is trying to push the ball but it is not moving
• A kid is taking a running start and kicks the ball and the ball goes over the net
• The other kid is standing still and the ball doesn't move far from him because he doesn't kick the ball as far as the kid who took a running start

What do you think?

• An object that is in motion will stay in motion
  • friction- a force that resists the object from moving across a surface
• The ball is being kicked by a larger force that keeps it moving
  • An object that is in motion will stay in motion until a force acts upon it
  • Newton's first law (Law of Inertia)states that an object in motion will stay in motion at a constant speed and travel in a straight line unless a force acts on it

Kepler 22b:

http://www.washingtonpost.com/national/nasa-finds-new-planet-kepler-22b-outside-solar-system-with-temperature-right-for-life/2011/12/07/gIQAPfzFdO_story.html
Scientists may have found a planet capable of sustaining life. Recently they have discovered that Kepler 22b is one of the closest earth-like planets out there. Scientists have found that this planet is right in the middle of the habitable zone and is a comfortable 72 degrees. It also has many earth-like qualities that lead scientists to believe that it is capable of sustaining life. It orbits a star similar to ours, the planet's year is 290 days similar to our 365 day year, and it is thought to have water and rocks. However, there are some downfalls. The planet is about 2 times the size of the earth. This could be too big to sustain life. Also, it is impossible for us to reach it. It would take 22 million for us to actually get to the planet because we don't have an instrument that travels at the speed of light. Even if we did it would take 600 years to reach it at the speed of light. We will just have to wait and see what happens with this.

Investigate

1.
a. starting point: 30cm
b. recovered point: 29.5cm
2.
a. A little less than half way up on the other side.
starting point: 20cm
estimated recovered point: 19.5cm
3.
a. starting point: 20cm, recovered point: 20cm--My prediction was off by .5cm. My prediction was close to the actual measurement but their was a random error.
b. The ball was dropped from 20cm and reached the same height on the recovered side.
5.
a. No, because the ball is loosing it's energy. Friction would eventually stop it
b. It would roll until something stopped it or it ran out of energy
c. Lack of friction would keep the ball rolling.

Do Now

• 4 meters on the opposite side
• A little less than 4 meters
• An object will stay in motion at a constant speed unless a force acts upon it, just like the skateboarder who starts at a certain speed and continues at that same speed

Physics Talk

• Galileo is a jack of all trades
• Law of Inertia- the tendency of an object to remain at rest or in motion in a straight line
• Newton's First Law- states that an object in motion will stay in motion at a constant speed and travel in a straight line unless a force acts on it
• Inertia- 1kg at 10m/s, 2kg at 5m/s, 5kg at 2m/s, 10kg at 1m/s
  • the natural tendency of an object to remain at rest or to remain moving with constant speed in a straight line
• force- a push or a pull
• An objects mass is a measure of its inertia
• The speed of the object thrown is the same speed as the hand that is throwing it
• The speed of the object thrown is the sum of the speed of the hand, elbow, and shoulder
• 
• speed- the change in distance per unit of time
• velocity- speed in a given direction
• acceleration- the change in velocity per unit of time
• An object at rest will stay at rest and an object in motion will stay in motion
• Frame of reference-a vantage point with respect to which position and motion may be described
  • the speed is dependent on your frame of reference
• 7m/s+3m/s= 10m/s
• 

Checking Up

1. Inertia is the natural tendency of an object to remain at rest or to remain moving with constant speed in a straight line
2. Newton's first law of motion states that an object in motion will stay in motion at a constant speed and travel in a straight line unless a force acts on it
3. A force
4. Friction
5. The bigger/heavier ball will be harder to stop than the smaller object
6. So you know the speed of the ball

Physics Plus

Physics To Go

1.
A) It will go until it runs into something that will stop it
B) Newton's First Law states that an object in motion will stay in motion at a constant speed and travel in a straight line unless a force acts on it. The ball from part A will stay in motion on a frictionless surface unless something stops it
2. 20m
3. I don't think that it is possible for a ball to roll in a straight line because their are hills and bumps. I feel that eventually the ball will start to slow down because their is nothing keeping it at the speed after a while
4. When a hockey player passes the puck to another player the puck stays at a constant speed in a straight line until the other player receives the puck and stops it with their own stick.
5. 2.5m/s+4.5m/s= 7m/s
6. 4.2m/s+10.3m/s= 14.5m/s
7.
A) 5.6+2.4=8m/s
B) 5.6-2.4= 3.2 m/s
C) a^2+b^2=c^2
5.6^+2.4^2= 37.12
c^2= 6.02m/s
8. 85-18= 67m/s
9.

A) 21.21
B) 43.9
C) 58
D) 172.1

Section 2

Learning Objectives

• Give examples of distance, time, speed, and acceleration
• Differentiate between instantaneous speed and average speed
• Recognize when motion is accelerated
• Calculate average speed and acceleration

What do you see?

• It is a like a strobe photo
• In the bottom picture he is running
• In the top picture he is walking
• The strides are bigger in the bottom picture

What do you think?

• 100mi/h looks and sounds fast but in reality 45m/s is faster

Investigate

1.
a) The dots will be a the same amount apart because it will be moving at constant speed
b) The dots will be further apart from each other
c) The dots will be closer together
d) It will start with the dots at same distance apart and then become further and further apart
6.
a)

7.
a) The tape was moved at the same speed making the distance between each dot the same size
b) It was constant speed with a little bit or error. We could tell because the amount of space between the dots were around the same
8.
a)

b)The smaller segments have less room between each dot and the bigger segments of paper have more room between the dots
c) yes, the smaller dots and spaces are on the smaller pieces of paper
9.
a) .04, .2, .04, .02, .3
b) The tape did not accelerate at a constant rate but they were all in the same range of each other

Physics Talk

• Acceleration- a change in the velocity of an object over time
• When the person was accelerating the distance between the dots were not equal
• Average speed- the distance traveled divided by the time it took to travel that distance
• 
• Instantaneous speed- the speed measured during an instant: the speed as the time interval approaches, but does not become zero
• 

Checking Up

1.
a) The distance between the dots is the same
b) The distance between the dots start with the same distance between them and the distance gets bigger and bigger as it gets faster
c) The distance between the dots will start with a bigger distance and gradually the distance will get smaller and the dots will become closer together
2. 400m/50s= 8m/s
3. Average speed is the distance traveled divided by the time it took to travel that distance. Instantaneous speed is the speed measured during an instant
4. 100kmh/10s= 10kmh/s

Physics To Go

1. Average speed is the overall speed and instantaneous speed is the speed at a given point
2.
a) 1000m/15s= 66.6m/s
b) 84m/6s= 14m/s
c) 9,600m/7,200= 1.33m/s
d) 400,000m/270s= 24.7m/s
3.
a) yes, negative
b) yes, positive
c) yes, positive
d) yes, negative
e) yes, positive
f) yes, positive
4.
a) D
b) B
c) A
d) C
e) A- positive
B- none
C- positive, then negative
d- positive
6.
a) -45kmh/9s= -5kmh/s
b) positive
7.
a) constant speed
b) constant speed gradually getting faster
c) constant, fast, constant
d) fast, slowed down, fast
8. 100m/2h= 50m/h
9. No this means that the overall/average speed was 15.
10.

11. 4= v/5
4*5=v
v=20m/s
12. bicycle- 6m/s
runner- 100/10= 10m/s
The runner will go faster that the bicycle

Section 3

Learning Objectives:

• Identify the forces acting on an object
• Determine when the forces on an object are either balanced or unbalanced
• Compare amounts acceleration semi-quantitatively
• Apply Newton's second law of motion
• Apply the definition of the newton as a unit of force
• Describe weight as the force due to gravity on an object

What do you see?

• A girl is trying to speed up to catch up with the ball
• She has to move faster to keep contact with the ball

What do you think?

• force- a push or a pull
• the ball with the bigger mass will be less affected by the force

Investigate

2. The car is going at a constant speed in a straight line
3.
a) It went faster
b) It went in a straight line but it just went faster
c) The car went faster will more force
d) The greater the constant force pushing on the object, the faster the object will go
4.
a) The object rolled faster because it not not weigh a lot
5.
a) The cart went slower because it had more mass on it
b) When equal amounts of a constant force are used to push objects having different masses, the more massive object the harder it is to push
6. It is harder to push a smaller object with a small force
8. The ruler bent a little bit because the penny is not very heavy
9.
a) The ruler bends further and further down every time a coin is added
b) A small force would be about 1 or 2 pennies. A large force would be like 3 or 4 pennies
c) Gravity

Physics Talk

• Newton's Second Law of Motion- the acceleration of an object is directly proportional to the unbalanced force acting on it and inversely proportional to the object's mass. The direction of the acceleration is the same as the direction of the unbalanced force
• 
• Newton's second law tells you that accelerations are caused by unbalanced force
• When you apply a force to an object that had a small mass, the acceleration will be smaller for the same force
• The acceleration gets less and less as the mass gets larger and larger
• weight- the vertical, downward force exerted on a mass as a result of gravity
• 
• gravity= -9.8m/s
• Free-body diagram- a diagram showing the forces acting on an object
  • Example:
  • Acceleration= 0
• 
• No change in speed or direction implies acceleration= 0
• 

Checking Up

1. An unbalanced force on an object produces acceleration. And a balanced force produces a=0
2. The acceleration increases because the object is harder to push
3. Gravity is -9.8m/s and you divide the acceleration by the gravity
4. Your weight increases and your mass stays the same.

Physics to Go

1.
A) F= (70)(5)= 350m/s
B) 800=(m)(10)= 80m/s
C) 70=(7)(a)= 10m/s
D) -1500=(100)(a)= -15m/s
E) F=(100)(-30)= -3,000m/s
2.
A) They are both objects in free fall, which means they have acceleration due to gravity which is 9.8
B) When the force is negative means that it is working against the object. When the acceleration is negative it is moving in the opposite direction.
C) Yes, because it is working against the running back
3. F=ma
42=(0.30)(a)
a= 140m/s
4. F=ma
F=(0.040)(20.0)
F=0.80N
5.
A) A bowling ball or baseball will stay in motion until it is caught by or stopped by a force. The mass is less making it easier to throw and catch.
B) The bowling ball or baseball will go in the direction that the force pushes it. The mass is more meaning it is harder to throw and catch
6. W= mg
w= (0.1)(-9.8)
w= -9.7kg
7.
A) Weight in Newtons=(150)(4.38)
Weight in Newtons= 657
B) w=mg
657= m(-9.8)
m= -67.0
10. 50+40= 90N
11. 200*4=800N
12. F=ma
125= (700)(a)
a=.18
13. Vr=130N, 67.4 degreees North of East

14. 38.65
15. F=ma
F= (12.8)(9.8)
F= 125.44
16.
A) 30.0+40.0= 70.0
B) 70= (5.6)(a)
a= 12.5
17.
A) 30.0-20.0= 10.0
B) 10= (100)(a)
a= .1
C) 50=(100)(a)
a=.5

Do Now 1/4/12

F=ma
65=(0.4)(a)
a= 162.5m/s

Physics Plus

1. 176.8, 45 degrees North of West

2.
A) 40+(-70)=30N South
B) Pythagorean theorem- 50N @37 degrees
C) 37 degrees South of West

Section 4

Learning Objectives:

• Apply the terms free fall, projectile, trajectory, and range
• Provide evidence concerning projectiles launched horizontally from the same height at different launch speeds(including zero launch speed)
• Explain the relationship between the vertical and horizontal components of a projectile's motion
• Recognize the factors that affect the range of a projectile
• Infer the shape of a projectile's trajectory

What do you see?

• The girl is dropping 2 apples. One straight down and the other was thrown
• The boy is timing both of the apples falling
• The apple's have the same amount of space between each interval

What do you think?

• height, air resistance, force

Investigate

Part A
1. yes
2. Both coins hit the floor at the same time
3.
a. No, the coins still hit the floor at the same time
b. yes, the second coin went further out than it did the first time I flicked it
c. (add sketch)
4.
a. They both hit the floor at the same time
b. The coin has less distance between the floor and the chair than the floor and the counter making the coin reach the ground faster
Part B
1.
a. The person in the chair will catch it even though he is moving forward
2.
a. The ball landed where he threw the ball
b. force applied to the ball, height, speed, mass, acceleration

Physics Talk

• projectile- an object traveling through the air or other medium
• 
• The projected coin has a constant speed to the right, when there is no air resistance
• The horizontal velocity remains the same, the vertical velocity is constantly changing
• 
• 

Checking Up

1. They will reach the ground at the same time if there is no air resistance
2. It's horizontal velocity will stay the same.
3. At the highest point the velocity is 0. The acceleration is -9.8.

Physics Plus

Section 6

Learning Objectives

• Provide evidence that forces come in pairs, with each force acting on a different object
• Use Newton's third law to analyze physical situations
• Describe how Newton's third law explains much of the motion in your everyday life

What do you see?

• the kid in the chair is pushing off of the wall
• he is accelerating backward (negative acceleration)
• the wall is curved to show how hard he is pushing

What do you think?

• you bend your knees and use the force from your body on the ground and as you push off, the ground is pushing back on you

Investigate

Part A
1.
a. Your motion is accelerated when you push off of the wall. You accelerate in the opposite direction of the wall
b. Your motion is at constant speed in the middle part of the acceleration. If you ignore the effects of friction then you would keep going until a force or object stopped you
c. The force of you pushing off of the wall and the force that the wall is applying back at you
d. You push against the wall in the opposite direction that you accelerate
e. The force that you exert on the wall is large so that you accelerate in the direction that is opposite of the force. The force exerted on you from the wall is not as great as the amount of force you put on the wall.
2.
a. Student A pushes off of student B and accelerates backward
b. The push off of student B's hands
c. Student B off of student A and accelerates backward
d. The push off of student A's hands
3.
a. The force of friction on the ground
b. No because regular shoes do not have any frictional pull on ice
4.
a. The person with the less amount of pull cannot get to the right amount because of the force of the other person
b. *add picture
Part B
3.
a. The ruler has mass added to it but it stays the same, there is no bend
4.
a. The deflection is 1 cm with 1300 grams
b. The more weight that was added to the meter stick the more it bent
c. yes, it is still deflecting but you just can't see it as much
d.

Physics Talk

• Acceleration is always accompanied by an unbalanced force, and the acceleration and the force are in the same direction
• Newton's 3rd Law- For every applied force, there is an equal and opposite force. The two forces always act on different objects
  • If you push on the wall, the wall pushes back on you with the same force
  • The push or force of the wall is equal and opposite to the force of the student on the wall
• 
• Free Body Diagram- a diagram showing the forces acting on an object
• 
• 

Checking Up

1. For every applied force, there is an equal and opposite force
2. The system that the earth rotates around
3. It shows the forces acting on an object

Physics to Go

1. No, because he is not pushing against the shot put
2. There is a slight deflection but it is too small for the eye to see. The more weight is added the more you can see the deflection
3. The weight that is added to pushes against the scale and the scale pushes back.
4. The force of the ball on the bat is stronger than the force of the bat on the ball
5. The force of the linebacker is much greater than the force of the running back
6. The player on the boards, the boards on the player
7. The glove protects their hands from the fast ball and the glove has a rounded part which is easier to stop

Section 7

Learning Objectives

• Apply the definition of the coefficient of sliding friction, mu
• Measure the coefficient of sliding friction between the soles of athletic shoes and a variety of surfaces
• Calculate the effects of frictional forces on the motion of objectives

What do you see?

• The guy in the first picture is sliding the shoe across the ice with no problem
• The guy in the second picture is having a hard time pulling the shoe because he is pulling it through sand
• She is pulling really hard in the sand

What do you think?

• Depending on the surface that you play on, you need shoes that give you traction and grip the ground

Investigate

1.
a. a leather boot
b. friction and different surfaces
3.
a. 1.6N on the classroom floor
4.2 N on the pavement
b. We know that we are pulling it at a constant speed because the number will stay the same throughout
c. 4.2/4.8= 0.875 mu (pavement)
1.6/4.8= 0.33 mu (classroom)
4.
a. 9.6N (boot in ugg)
5.4N (classroom)
6N (pavement)
b. 5.4/9.6= .5625 mu
6/9.6= .625 mu
c. There is always a chance of possible error to occur. I think that the weight of the shoe affects the mu
d. If an athlete wears heavy shoes, then it will affect their mu
5.
a. *add picture
b. 6N on the pavement (.625 mu)
c. classroom= .5625 mu
pavement= .625 mu, the friction could affect the mu
d. I think that the weight affects the mu so the mu will change depending on if it is empty or weighed down

Physics to Go

1. Football, because when it snows or rains the field can become very slippery. To increase friction the athlete could get cleats with longer spikes on the bottom
2. Hockey, they would have the Zamboni clean the ice to make it as smooth as possible
3. How new or old the floor is and if it is cleaned often
4. They don't have to run a lot
5. ??????
7. I think they put up more of a resistance when your speed increases
9. They could say: It is proven in this study that this shoe has this much friction
10. Friction helps running because it helps keep your feet on the ground and at a steady pace. Cleats are good for football and soccer because they help your feet stick into the ground.

Section 8

Learning Objectives:

• Apply equations for kinetic energy, gravitational potential energy, and elastic potential energy
• Recognize that restoring forces are active when objects are deformed
• Apply the equation for the force necessary to compress or stretch a string
• Measure the transformations among the different forms of energy
• Conduct simulations of the transformations of energy involved in the pole vault

What do you see?

• A guy is getting running(accelerating)
• He is pole vaulting over a building

What do you think?

• The pole is too big
• weight, height, pole weight

Physics Talk

• When a force acts on an object, the speed and position of the object may change
• kinetic energy- energy associated with motion
• gravitational potential energy- the energy an object posses because of its vertical position from Earth
• potential energy- energy associated with position
• law of conservation of energy- energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant
• work- the product of the displacement and the force in the direction of the displacement
• elastic/ spring potential energy- the energy of a spring due to its compression or stretch

Section 9

Learning Objectives

• Measure changes in height of the body's center of mass during a vertical jump
• Calculate changes in the gravitational potential energy of the body's center of mass during a vertical jump
• Apply the definition of work
• Recognize how work is related to energy
• Apply the joule as a unit of work and energy using equivalent forms of the joule
• Describe the concepts of work and conservation of energy to the analysis of a vertical jump, including weight, force, height, and time of flight

What do you see?

• The ice skater is doing a jump
• The person in the helicopter is timing the hang time

What do you think?

• They put a lot of force into the jump that they do

Investigate

1.
a. 21
b.21/30= .7
c. It appears that he does, but they actually do not
2.
a. 32
b. 32/30= 1.067
3.
a. 569N
b. 569= m(9.8)
m= 58.06kg
4.
a. 100-21= 79cm= .79m
5.
a. 110cm= 1.1m
b. 1.1-.79= .31m
6.
a. went from 50 to 20= 30cm=.3m
7.
a. GPE= (58.06)(9.8)(.3)
GPE= 170.7 J
b. EPE= 1/2kx^2
EPE= 1/2k(.3)^2
EPE= 3,793.33
c.

Notes

center of mass

• one point where the average mass of an object is located
• the center of mass MUST be above the base to be balanced