KINEMATICS

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KINEMATICS

• 4TH ESO
• Chemistry and Physics
• IES AMES

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DESCRIBING MOTION

• Physics progresses not by revolutions, which do
  away with all that went before, butrather by
  evolutions, which exploit the best about what
  isalready understood. Newton'slaws will
  continue to be as true today, no matter what
  wediscover at the frontiers of science.
• Lawrence M. KraussThe Physics of Startrek

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DESCRIBING MOTION
Beyond the palace hemi-powered drones scream down
the boulevardThe girls comb their hair in
rearview mirrorsAnd the boys try to look so
hardThe amusement park rises bold and starkKids
are huddled on the beach in a mistI wanna die
with you wendy on the streets tonightIn an
everlasting kissThe highways jammed with broken
heroes on a last chance power driveEverybodys
out on the run tonight but theres no place left
to hideTogether wendy well live with the
sadnessIll love you with all the madness in my
soulSomeday girl I dont know when were gonna get
to that placeWhere we really want to go and well
walk in the sunBut till then tramps like us baby
we were born to run Bruce Springsteen

• In the day we sweat it out in the streets of a
  runaway american dreamAt night we ride through
  mansions of glory in suicide machinesSprung from
  cages out on highway 9,Chrome wheeled, fuel
  injected and steppin out over the lineBaby this
  town rips the bones from your backIts a death
  trap, its a suicide rapWe gotta get out while
  were youngcause tramps like us, baby we were
  born to runWendy let me in I wanna be your
  friendI want to guard your dreams and
  visionsJust wrap your legs round these velvet
  rimsAnd strap your hands across my
  enginesTogether we could break this trapWell
  run till we drop, baby well never go backWill
  you walk with me out on the wirecause baby Im
  just a scared and lonely riderBut I gotta find
  out how it feelsI want to know if love is wild,
  girl I want to know if love is real

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DESCRIBING MOTION

• Kinematics is the science of describing the
  motion of objects using words, diagrams, numbers,
  graphs, and equations.
• The goal of any study of kinematics is to develop
  sophisticated mental models which serve to
  describe (and ultimately, explain) the motion of
  real-world objects.
• In this chapter you will learn
• How to describe motion in terms of distance,
  displacement, velocity, acceleration and time.
• How to use equations to link these quantities
• How to draw and interpret graphs representing
  motion

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DESCRIBING MOTION
Is she in motion? How can she estimate her
arrival time? How far the car has moved? How fast
the car has moved?
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DESCRIBING MOTION

• Physics is a mathematical science - that is, the
  underlying concepts and principles have a
  mathematical basis.
• The motion of objects can be described by words -
  words such as distance, displacement, speed,
  velocity, and acceleration. These mathematical
  quantities which are used to describe the motion
  of objects can be divided into two categories.
  The quantity is either a vector or a scalar.
  These two categories can be distinguished from
  one another by their distinct definitions
• Scalars are quantities which are fully described
  by a number alone.
• Vectors are quantities which are fully described
  by both a number and a direction.

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DESCRIBING MOTION

• In science we define motion as the change in
  position with time.
• How fast an object changes position or the rate
  that an objects position changes with time is
  called the speed.
• If we know both the direction in which an object
  moves and its speed, then the combined direction
  and speed are called the velocity of an object.
  When either the speed or the velocity of an
  object is zero, then there is no motion.

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DESCRIBING MOTION

• Distance and displacement are both ways of
  measuring how far an object has moved.
• Distance is a scalar quantity which refers to
  "how much ground an object has covered" during
  its motion.
• Displacement is a vector quantity which refers to
  "how far out of place an object is" it is the
  object's change in position. Displacement is the
  distance moved in a particular direction.

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DESCRIBING MOTION
DISTANCE/DISPLACEMENT
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DESCRIBING MOTION

• Speed and velocity are both ways of measuring
  how fast an object has moved.
• Speed is a scalar quantity which refers to the
  rate of change of distance.
• average speed distance travelled (m)/ time
  taken (s)
• Velocity is a vector quantity which refers to
  the rate of change of displacement.
• average velocity total displacement (m)/ time
  taken (s)
• Instantaneous velocity it is the actual velocity
  of the car. To find it we have to find the
  displacement over a very small time interval.
• The smaller the time interval, the closer we get
  to an instantaneous value

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DESCRIBING MOTION

• Acceleration is a vector quantity which refers to
  the rate of change of velocity.
• average acceleration change in velocity (m
  s-1)/ time taken (s)
• The change in velocity may be a change in
  speed, or direction or both.

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DESCRIBING MOTION

• DISPLACEMENT-TIME GRAPHS
• The gradient of a displacement-time graph gives
  us the velocity.
• The steeper the gradient, the greater the
  velocity.

Positive Velocity Constant Velocity
Positive Velocity Changing Velocity
(acceleration)
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DESCRIBING MOTION

• VELOCITY-TIME GRAPHS
• The gradient of a velocity-time graph gives us
  the acceleration.
• The area under a velocity-time graph also gives
  us the displacement.

Positive Velocity Constant Velocity No
acceleration
Positive Velocity Changing Velocity
(acceleration)
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DESCRIBING MOTION

• GRAPHS INDICATING /- VELOCITY AND ACCELERATION

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DESCRIBING MOTION

• DESCRIBING MOTION WITH EQUATIONS

a acceleration v velocity u initial
veloctiy x position x0 initial position t time
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DESCRIBING MOTION

• VERTICAL MOTION UNDER GRAVITY
• FREE FALL An object is in free fall if the
  only force acting on it is the gravity. All the
  objects in free fall accelerate downwards at the
  same rate. a - g - 9,8 ms-2

g gravitational field strength v velocity u
initial veloctiy x position x0 initial
position t time
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DESCRIBING MOTION

• VERTICAL MOTION UNDER GRAVITY
• TERMINAL VELOCITY On Earth, falling object
  always experience some Air Resistance. The air
  resistance is not constant, it increases with
  speed.
• Eventually the air resistance and weight will
  balance out. At this point the object stop
  accelerating and is travelling at the maximum
  possible speed or terminal velocity.

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DESCRIBING CIRCULAR MOTION

• Uniform circular motion is the motion of an
  object in a circle with a constant or uniform
  speed.
• An object moving in uniform circular motion
  would cover the same linear distance in each
  second of time.
• The distance of one complete cycle around the
  perimeter of a circle is known as the
  circumference

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DESCRIBING CIRCULAR MOTION

• MEASURING ANGLES
• Radian
• The word radian describes a certain size of an
  angle. For an angle of one radian the arc length
  along the edge of the circle is equal in length
  to the radius.
• If you want to know the exact size of the radian
  in terms of degrees, take 360 and divide it by 2
  times pi. That number is how many degrees there
  are in a radian.
• How many radians are there in a circle? 1 circle
  360º 2p rad

Angle (rad) length of arc/radius For a full
circle Angle 2pr/r 2p rad
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DESCRIBING CIRCULAR MOTION

• TIME PERIOD AND FREQUENCY
• TIME PERIOD (T)
• It is the time (s) for a complete rotation
• FREQUENCY
• It is the number of rotations per second (Hz)
• T 1/f

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DESCRIBING CIRCULAR MOTION

• ANGULAR SPEED
• For an object rotating about an axis, every
  point on the object has the same angular speed.
  Angular speed has the units rad/s.
• Angular speed is the rate of change of angular
  displacement and can be described by the
  relationship
• wq/t
• We can also calculate the angular speed if we
  know the time period or the frequency of the
  motion.
• wq/t 2p/T 2pf

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DESCRIBING CIRCULAR MOTION

• LINEAR SPEED
• We can calculate the linear speed at any
  instant
• vs/t
• LINKING v AND w
• Speeddistance/time taken
• v 2pr/t w.r