Yes,%20you

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Chapter 8

• Yes, youre taking notes, didnt I just give you
  an outline?

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Motion

• What is motion?
• If I threw a ball from here to there, can you
  tell me when the ball is in motion and when it
  isn't?

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• Motion ? location
• In math, ? means "change in"
• What could affect the motion of the ball?
• How hard I throw the ball I can change the speed.

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• Change in speed
• Faster means it has to go the same distance in a
  shorter time.
• Slower means it has to go the same distance in a
  longer time.
• Think about when you're running to class
• Gym - - - - - - - - - - - - - - - - - - - - -
  -Classroom
• When you are late to class you run through the
  halls
• When you are early you strut down the halls

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Speed

• Speed ? Distance
• ? Time

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• Various speeds
• These are all different numbers that have the
  same values they have different units of
  measure.
• Note Always pay close attention to units of
  measure, your units should always agree with
  what's asked for in a question.

To be measured Miles per hour Mile per second Feet per second
Turtle 0.25 0.00006 0.3
Rifle bullet 2045 0.57 3,000
Columbia shuttle 12,000 3.3 17,598
Earth's orbit 40,000 11.1 58,666
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• Speed how fast something is moving
• on average over time AVERAGE SPEED
• at an exact moment INSTANTANEOUS SPEED

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• Average speed Total Distance traveled
  Time taken to
  travel Distance
• Average speed The average overall speed on a
  trip
• Example 2 hours in the car to travel a distance
  of 100 miles
• Equation 100 miles 50 MPH
  2 hours

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• Instantaneous speed The speed you are traveling
  at that exact moment
• Example During a 2 hour trip over 100 miles
• stop at a red light 0 MPH
• speed at 75 MPH on the highway
• slowly driving at 25 MPH past a school

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• Image for remembering equations for speed math
  problems

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Velocity

• Velocity Speed and direction
• Measured by a speedometer and a compass
• Velocity ? Distance direction of movement
• ? Time
• In this class we will use the terms
  interchangeably and imply the direction.
• However
• CONSTANT SPEED ? CONSTANT VELOCITY

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• The car can be traveling at the same speed, but
  has changes in direction
• Changes in velocity can have different causes
• ? V same speed ? direction
• ? V ? speed same direction
• ? V ? speed ? direction

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Mathematical Graphic Representations of Velocity

• If we know the average speed, we can plot the
  time and distance along a trip

Distances Traveled (miles) Distances Traveled (miles) Distances Traveled (miles)
Time (hours) Car A at 15 MPH Car B at 30 MPH Car C at 60 MPH
0.5 7.5 15 30
1 15 30 60
1.5 22.5 45 90
2 30 60 120
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• What do you notice about the 3 lines on the Car
  Speed graph?
• Steepness of line greater the slope of the line
• the greater the slope, the faster the speed of
  the car
• slope ? Y or rise
• ? X run

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• If distance is placed on the y-axis and time is
  placed on the x-axis,
• Velocity ? D ? Y Slope of line
• ? T ? X
• So, Velocity Slope of line
• Car A Slow Gradual line
• Car B Medium Medium
• Car C Fast Steep line

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Graphing Velocity (Average Speed)

• What can you tell from different graphs?

• 3 Different objects moving at 3 different speeds

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• Stopped Object Time passes but distance does not
  change
• No movement

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• Backward moving object
• The distance is decreasing, so there is movement
  towards the source

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• Circular Motion Time passes as the same
  distances are revisited like a race track

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• Series of motions
• Rest-forward-rest-backward-rest
• Note does not represent the profile of the
  terrain

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Velocity Graphs and Profiles of Terrain

• What do we know about movement?
• 1 rest
• 2 gradual movement forward
• 3 rest
• 4 backward movement
• 5 rest

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Velocity Graphs and Profiles of Terrain

• 1 You are halfway up a hill, at rest holding a
  wagon.
• 2 You start moving uphill
• 3 You take a rest
• 4 The wagon handle slips out of you hand and
  travels backward down the hill.
• 5 The wagon stops moving at the bottom of the
  hill.

• What could be a possible explanation pulling a
  wagon uphill?

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Dimensional Analysis Unit Analysis

• In your head, you can probably convert
• inches to feet
• sure, 12 in 1 ft
• inches to yards
• okay, 3 ft in 1 yd 36 in
• inches to miles
• um, probably not

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• FAQ When I convert from inches to yards or yards
  to inches, when do I multiply and when do I
  divide?
• The easiest way to approach these unit
  conversions is by using dimensional analysis.

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• There are 4 rules
• 1. If you use only one unit to start, put it over
  a 1.
• 2. Determine the conversion factors. (Ex 12
  inches 1 ft) and put into a fraction.
• 3. Properly place the conversion factors in an
  equation.
• 4. Check cancellations of units so that you are
  left with the unit you were looking for on the
  top of a division bar. The units that are
  canceled should be on opposite sides of the
  division bar.

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• Example 1 How many feet in 13 in? 1 1/12 or
  1.083 ft
• Step 1 starting with 13, so 13 inches
• 1
• Step 2 conversion factors 1 foot or
  12 inches
• 12 inches 1 foot
• Step 3 place factors 13 inches x 1 foot
  
• 1 12 inches
• Step 4 check cancellations 13 inches x
  1 foot
• 1 12 inches
• 13 inches 1.083 ft

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• Example 2 Convert 13 inches into yards.
• Step 1 starting with 13, so 13 in
• 1
• Step 2 conversion factors 1 ft 1
  yd
• 12 in 3 ft
• Step 3 place factors 13 in x 1 ft x 1
  yd
• 1 12 in 3 ft
• Step 4 check cancellations 13 in x 1 ft x 1
  yd
• 1 12 in 3 ft
• 13 in 0.36 yd

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• Example 3 Convert 2 years into seconds.
• 2 yrs x 365 days x 24 h x 60 min x 60 sec
  
• 1 1 yr 1 day 1 h
  1 min
• 2 yrs 63,072,000 sec

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• Example 4 Convert 4 decades into minutes.
• 4 dec x 10 yrs x 365 days x 24 h x 60
  min
• 1 1 dec 1 yr 1 day
  1 h
• 4 decades 21,024,000 m

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• Example 5 I am 5 3 or (5 x 12) 3 63 inches
  tall. How many cm tall am I?
• 63 in x 2.56 cm
• 1 1 in
• 63 in 160.1 cm

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• Dimensional Analysis Worksheet
• 1. In New Jersey, students in public schools go
  to school for 4 years. How many minutes are
  students enrolled in high school?
• 4 years x 365 days x 24 h x 60 min
• 1 1 yr 1 day 1
  h
• 4 yrs 2,102,400 min

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• 2. Alaynas dog is 3 ft tall. What is the dogs
  height in mm?
• 3 ft x 12 in x 2.54 cm x 10 mm
• 1 1 ft 1 in 1 cm
• 3 ft 914.4 mm

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• 3. Brian and Jesse were on a bus trip going 50
  MPH. For some extra fun, they decided to convert
  the buss speed into km/h. What should their
  answer be?
• 50 miles x 1.61 km
  1 hr 1 mile
• 50 MPH 80.5 km/h

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• 4. Driving home from practice, Alexs mother was
  driving at a speed of 30 m/s. What was their
  speed in km/h?
• 30 m x 1 km x 60 s x 60 min
  1 s 1000 m 1 min 1 h
• 30 m/s 108 km/h

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• 5. Saskia was riding her bike down the road at a
  speed of 5 km/h. What was her speed in m/s?
• 5 km x 1000 m x 1 hr x 1 min
  1 h 1 km 60 min 60 s
• 5 km/h 1.39 m/s

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• Class experiment
• Determine how tall you are in inches.
• 2. Using the conversion factor 1 mile 1.61
  km, determine how tall you are in cm.
• 3. Check your answer with a meter stick.

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Acceleration

• When you accelerate, what are you doing?
• Speeding up accelerating
• When you slow down, what are you doing?
• Decelerating
• In physics, we use the same term, acceleration
  for both speeding up and slowing down. We
  distinguish between the two by assigning positive
  or negative values.
• acceleration as in speeding up ? positive
• - acceleration as in slowing down ? negative

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• Acceleration the change in velocity over time
• - measured in m/s or m/s2
• s
• Acceleration ? Velocity
• ? Time

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• Acceleration ? Distance Direction
• ? Time
• ?
  Time
• Given an object moving in a circle
• - ? velocity due to a ? direction
• - if ? velocity, the ? acceleration as well
• - circular motion ? D ? V ? A

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Graphing Acceleration

• A ? V and slope ? Y
• ? T ? X
• Acceleration ? V ? Y Slope of line
• ? T ? X
• So, Acceleration Slope of line
• Steep slope fast movement
• Gradual slope slow movement

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• Acceleration Deceleration

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• Steepness of the line indicates the degree of
  acceleration

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Comparing Velocity and Acceleration

• Velocity ? Distance Acceleration ?
  Velocity
• ? Time ? Time

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• These two lines indicate the exact same thing?
  the same rate of acceleration
• Acceleration slope
• Deceleration - slope

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• When object is a rest ? Velocity is zero
• If ? Distance 0, then ? Velocity so
  Acceleration 0

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• When acceleration equals zero
• A ? V ? no change in velocity
• ? T ? Time will always pass
• No change in velocity
• - no velocity V 0 then object is at rest
• - constant velocity - ? V Vfinal Vinitial
• Vf 50 miles/h and Vi 50 miles/h
• Then ? V 0

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• If acceleration zero, you are either stopped or
  on cruise control
• To determine which, you must find if there is a
  change in distance.

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How it all fits together

• From Motion ? Acceleration only one variable is
  added at a time
• 1. Motion ? Distance
• 2. Speed ? Distance
• ? Time
• 3. Velocity ? Distance Direction
• ? Time
• 4. Acceleration ? Distance Direction
• ? Time
• ? Time

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Momentum

• When an object is in motion, we think velocity.
  However, we must not forget Momentum which is
  also acting on the object.
• Momentum a quantity defined as the product of
  an objects mass and its velocity.
• - In a formula, P momentum.
• - momentum moves in the same direction as the
  velocity

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• P Mass x Velocity
• - Measured in kg?m/s

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• Momentum and ? Velocity
• - large momentum, difficult to change velocity
• - small momentum, easier to change velocity
• Class Experiment Red light, green light
• Stationary objects have momentum of zero
• Why? No motion no speed no velocity no
  momentum

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• Momentum is directly proportional to mass
  momentum increases as mass increases.

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Force

• Force the cause of acceleration or a change in
  velocity
• - force is measured in units called Newtons
• Net force the combination of all the forces
  acting upon an object.

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• The size of the arrow represents the amount of
  force
• The arrows are the same so there is no movement.

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Friction

• Friction the force between two objects in
  contact that opposes the motion of either object.
• Pretend you are in a helicopter looking down on a
  ski slope in early spring. The ice is melting.
  Patches of dirt and gravel begin to show

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• How much friction?
• Skis snow little friction skis move over
  snow
• Skis dirt a lot of friction skis do not
  move over dirt
• Air resistance is a type of friction.

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Gravity

• Gravity Force of attraction between 2 objects
  due to their masses.
• The force of gravity is different on different
  planets, moons etc.
• On earth g 9.8m/s2
• Gravity depends upon the masses as well as the
  distance between objects.

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Newtons Laws of Motion

• Newtons 1st Law- the law of inertia
• An object at rest remains at rest and an object
  in motion remains in motion unless it experiences
  an unbalanced force.

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• Example 1 Whiplash Person B is stopped at a
  traffic light. Person A is not paying attention,
  and rear-ends Person B.

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• Result Person B moves forward suddenly Their
  head snaps back as it attempts to remain at
  rest. Their body, attached to the seat moves
  forward their head snaps forward to catch up
  with the body resulting in whiplash.

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• Example 2 Bus ride - The bus driver does not
  like children. Every time, they get too loud, he
  slams on the breaks. Why does he do this?
• Inertia The tendency of an object to remain at
  rest or in motion with a constant velocity. All
  objects have inertia because they resist changes
  in motion.

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• Trivia If two people on a space ship (in space)
  get into a physical fight, which will win?
• Person A Person B

Even though they are weightless there is no
gravity Person A has a greater mass, therefore, a
greater inertia.
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• Newtons 2nd law of Motion- the law of
  acceleration
• The unbalanced force acting on an object equals
  the objects mass times its acceleration.
• Force Mass x Acceleration

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• Example pushing a cart
• The greater the mass, the more force needed to
  cause acceleration.

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Bumper cars
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• Newtons 3rd law of Motion- the law of
  interaction
• For every action, there is an opposite and equal
  reaction force.
• Forces occur in pairs

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• Example Holding up a wall