Class Notes 4.18.11 Bouncing ball lab .PE

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• Class Notes 4.18.11 Bouncing ball lab .PE
• Lab Finding PE (Mass)
• Equation Sheet
• Reading Notes
• Bouncing Ball Physics

Bouncing ball lab is due Wednesday by 3pm.
Retake TEST by Thursday 4.21.11 Hw LATE -50 Twin
Towers worksheet Late -30
http//www.phy.ntnu.edu.tw/ntnujava/index.php?topi
c345
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Page 5 space 3
CONDITIONS FOR USE Use to find the COR, Or to
predict how high a resilient object will rebound

• Coefficient of Restitution (ELASTICITY) e no
  label
• Coefficient of Restitution COR no label
• Height bounce hB meters
• Height of the drop hD meters

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Coefficient of Restitution(COR)

• A COR of 1 would be a perfectly elastic collision
• A COR of 0 would be a perfectly inelastic
  collision.
• COR 0 e 1
• We have dropped various balls and found the
  Elastic Coefficient of Restitution

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Making restitutionreturn to the way it was

• IF someoneTakes 300 -- repay 300
• 100 restitution
• Shoplift and do community service
• lt100restitution

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Approximate coefficient of restitution for different types of balls Approximate coefficient of restitution for different types of balls
type of ball coefficient of restitution
Superball 0.9
Tennis ball 0.75
Baseball 0.55
Foam rubber ball 0.30
Beanbag 0.05
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Calculate the Potential energy from the drop
height and the bounce height page 5 space 4
Always positive!
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Bouncing Ball

• When the bottom gets flatter
• energy is changed to stored energy in the bonds
  of the ball
• by the bending of the material of the ball

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A boulder resting at the top of a hill has
potential energy.

• Gravitational Potential Energy is the energy
  stored due to height.
• Work can change the height of the Boulder
• Work can change the potential energy of the
  Boulder

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We Graphed all three points, but Average the
three trials for PE
Drop Height Bounce 1 Height Bounce 2 Height Bounce 3 Height Average Bounce height
20 H20
40 H40
60 H60
80 H80
100 H100
120 H120
140 H140
160 H160
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Use the average height for PE
Drop Height hD (cm) Average Bounce Height hB (cm) Drop PEDmghD Bounce PEcBmghB ? PE (PEB-PED)
20
40
60
80
100
120
140
160
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Use the Masser to find the mass in grams

• Be sure to use the same tray of spheres.
• There is only one masser, so please work
  carefully and quickly.
• Be sure the spheres are in the same tray when you
  finish.

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Mass of bouncing ballThen find PE in kg and
meters

• Find the mass on the balance (take turns)
  Record the mass in grams on the data table
• Convert the mass to kg ( divide by 1000)
• EX 35.7 g .037 kg
• Convert the height to m (divide by 100)
• Calculate the PE for the original height (in
  meters) and the first bounce and record it on
  the data table you may use 10 m/s/s for the ag
  in the equation
• PE mgh

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A bouncing basketball captured with a
stroboscopic flash at 25 images per second.
Ignoring air resistance, the square root of the
ratio of the height of one bounce to that of the
preceding bounce gives the coefficient of
restitution for the ball/surface impact.
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Potential energy changes to kinetic energy due to
work done by gravity
PE
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Bouncing of ball

• If a soccer ball is dropped on a hard surface, it
  will bounce back to a height lower than its
  initial position. Such kind of motion is called
  the bouncing of the soccer ball, which plays an
  important role in the motion of the ball. Let us
  study the mechanism of the bouncing of the ball
  in details.

• The relative bounciness of different types of
  balls

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• The coefficient of restitution is how you
  quantify bounciness or give bounciness a number,
  and you do that by dividing the bounce height by
  the drop height, then finding the square root of
  that. When... Read more http//wiki.answers.com
  /Q/What_is_the_Coefficient_of_Restitution_of_bounc
  ing_a_basketballixzz1JW73FiKE

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• As a result, a ball with smaller coefficient of
  restitution rebounds to lower height in
  successive bounces and a shorter time is required
  for the ball to stop (see below figure). For
  example, grass reduces the coefficient of
  restitution of a soccer ball since the bending of
  blades causes further loss of its kinetic energy.
  Therefore, it would take a shorter time for the
  soccer ball to stop if it is kicked on grass
  instead of hard floor.

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The Total Mechanical Energy

• As already mentioned, the mechanical energy of an
  object can be the result of its motion (i.e.,
  kinetic energy) and/or the result of its stored
  energy of position (i.e., potential energy). The
  total amount of mechanical energy is merely the
  sum of the potential energy and the kinetic
  energy. This sum is simply referred to as the
  total mechanical energy (abbreviated TME).
• TME PE KE
• As discussed earlier, there are two forms of
  potential energy discussed in our course -
  gravitational potential energy and elastic
  potential energy. Given this fact, the above
  equation can be rewritten
• TME PEgrav PEspring KE

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Mechanical Energy as the Ability to Do Work
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changing its temperature.

• We can also change the bounciness of a ball by
  changing its temperature. Take two baseballs that
  bounce to about the same height. Put one in the
  freezer for an hour and leave the other at room
  temperature. Then compare their bounciness again.
  You should notice that the room temperature ball
  bounces a little bit higher. The cold ball would
  bounce about 80 percent as high as the room
  temperature ball. Although the difference of
  bounciness is not dramatic, it's enough to see
  that temperature can be a factor it could make
  the difference between a home run and a pop fly.
• However, the change in bounciness due to the
  change in temperature is taken for granted for
  some sport. For example, squash player rely on
  the pre-game warm up to warm up the ball as well
  as the players.

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Surface bounced on

• Examplegrass reduces the coefficient of
  restitution of a soccer ball since the bending of
  blades causes further loss of its kinetic energy.
  Therefore, it would take a shorter time for the
  soccer ball to stop if it is kicked on grass
  instead of hard floor.

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• Coefficient of restitution of a tennis ball is
  0.712. Thanks ...

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                                                1910 soccer ball ii                                                    1950 soccer ball ii                                                    2004 Euro Cup ball ii

• 1910 soccer ball ii 1950 soccer ball ii
  2004 Euro Cup ball ii
• In the late 1980s, the leather casing ball was
  replaced by totally synthetic ball in soccer
  competitions. The covering material of the
  totally synthetic ball is synthetic leather made
  from polymer. For high quality ball, the casing
  is made of the synthetic leather panels stitched
  together through pre-punched holes by waxed
  threads. The bladder of a totally synthetic ball
  is usually latex or butyl bladder. The ball is
  then inflated by pumping air into its bladder
  through a tiny hole on the casing. The totally
  synthetic ball could resist water absorption and
  reliably maintain its shape.
• The Internal structure of a totally synthetic
  soccer ball ii
• Nowadays, the official soccer rules called the
  "Laws of the game", which are maintained by the
  International Football Association Board (IFAB),
  specify the qualities of the ball used in soccer
  matches. According to the laws, the soccer ball
  should satisfy the following descriptions
• it is spherical in shape,
• its casing is made of either leather or other
  suitable material,
• its circumference is not more than 70 cm and not
  less than 68 cm,
• its weight is not more than 450 g and not less
  than 410 g at the start of the match.
• its pressure inside equal to 0.6 - 1.1 atmosphere
  at sea level.

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Figure explaining the extra pressure inside the
soccer ball.
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The relative bounciness of different types of
balls iii
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• Energy change in the falling ball after release
  until hitting on the ground.(Note that here
  "G.P.E." and "K.E." stand for the gravitational
  potential energy and kinetic energy
  respectively.)

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Work must be done in order to distort an elastic
object

• . Therefore, if you pull a spring outward so that
  it become longer, some energy must have been
  transferred from yourself to the spring. The
  energy stored in an distorted object due to its
  deformation is called the elastic potential
  energy. So, when talking about the elasticity of
  the ball, we are indeed talking about the
  spring-like behavior of the ball. In other words,
  we are considering the tendency of the ball to
  return to its original spherical shape when it is
  being squeezed. Where does the elasticity of the
  ball come from? The elasticity of a solid ball
  arises from the elasticity of the constituting
  material which is due to the interatomic or
  intermolecular force inside. In contrast, for
  air-filled ball like soccer ball, its elasticity
  is resulted from the extra air pressure inside
  the ball. What happens to a ball after you
  dropped it above a hard floor? The gravity pulls
  the ball toward the ground and thus the ball
  falls leading to the lost of its gravitational
  potential energy. By the law of conservation of
  energy, the ball must gain kinetic energy and so
  it falls towards the ground with an increasing
  speed. Subsequently, the ball hits the hard floor
  with a high speed. (Note that the ball always
  moves with the downward acceleration of g 9.8
  m/s2 as it falls.)

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The elasticity of an object means

• the tendency of the object to return to its
  equilibrium shape, the natural shape of the
  object with no net force applied on it, when it
  is being deformed. And the force for the object
  to restore to its equilibrium shape is called the
  restoring force, which is always directed in
  opposite to the deformation of the object. Almost
  all real rigid body are elastic, i. e. having
  certain extent of elasticity. A trivial example
  of an elastic object is the spring. You probably
  have the experience that a spring would tend to
  restore to its original size when you stretch it
  to be longer. Scientist found that, providing the
  deformation is not too large, the relationship
  between the distortion and the restoring force is
  given by the Hooke's law"The restoring force
  exerted by an elastic object is proportional to
  how far it has been distorted from its
  equilibrium shape." The restoring force Fs on a
  spring in case of different extension.

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Law of conservation of energy

• In the law of conservation of energy, it was
  stated that"Energy can neither be created or
  destroyed but can only be changed from one form
  to another."Therefore, the amount of total
  energy in an isolated system must be constant.
  For example, let us consider a piece of charcoal
  placed in an isolated room. If we burn the
  charcoal, the chemical energy inside the charcoal
  is changed into the thermal energy of the room.
  Then the temperature inside the room would be
  increased. When the ball hits the ground, the
  ball exerts force on it. By the Newton's 3rd law
  of motion, the ground exerts a force on the ball
  as well. The motion of the ball would be stopped
  by the (stationary) hard floor resulting in the
  compression of the ball. So the work done on the
  ball leads to the increase of the elastic
  potential energy of the ball. That means some of
  the kinetic energy of the ball (which is
  converted from the gravitational potential energy
  of the ball) is converted into the elastic
  potential energy when the ball hits the ground.
  On the other hand, some of the kinetic energy is
  lost as thermal energy during the impact due to
  either the internal friction of the ball or the
  heating of the surface.
• Energy change in the falling ball during the
  impact

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After losing all the kinetic energy, the ball
becomes momentarily at rest.

• The squashed ball would simply act like a
  compressed spring. The ball pushes the ground
  with a restoring force proportional to its
  displacement from the equilibrium position
  (Hooke's law). In consequence, the ground pushes
  back the ball with a force of equal magnitude but
  opposite in direction. Thus the ball bounces back
  in upward direction. During the rebound, the
  stored elastic potential energy is released as
  the kinetic energy of the ball which is then
  converted to gravitational potential energy as
  the ball moves up. Moreover, some of the elastic
  potential energy is lost again due to friction or
  heat which results in slight heating of the ball.
  The ball keeps on going upward until it comes to
  rest after losing all its kinetic energy again.
  Due to the lost of some of the initial
  gravitational potential energy into thermal
  energy, the ball cannot bounce back to the
  original height.

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What is the Coefficient of Restitution?(also
called Elastic Coefficient)

• What is the slope of each of the graphs?
• Use the slope of the graphs to find the
  Coefficient of Restitution, just like we did for
  the Spring Constant.
• The Coefficient of Restitution tells us how
  springy the ball is.
• The slope of the graph represents this constant.
  The constant will be the same for a given ball.

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PE Bouncing Ball Lab

• Work and Potential Energy and Problems
• Patterns in graphs
• Increasing/decreasing/ no change
• Linear or curved line of best fit.

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Bouncing ball labmeasure height at the first
bounce up and the second bounce
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Work to PEor PE to work

• a force acts upon it and changes the height

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Measurement of Horsepower

• The maximum horsepower developed by a human being
  over a few seconds time can be measured by timing
  a volunteer running up the stairs in the lecture
  hall.
• If a person of weight W runs up height h in time
  t, then h.p. Wh/t X 1/550 ft-lbs/sec.
• A person in good shape can develop one to two
  horsepower. It will be entertaining to the
  students if the professor tries it too.
• Should the person be allowed a running start?

http//www.physics.ucla.edu/demoweb/demomanual/mec
hanics/energy/faith_in_physics_pendulum.html
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Bouncing Ball

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Bouncing a Ball

• What you need
• a tennis ball
• a basketball
• a room without breakables
• InstructionsDrop the tennis ball from waist
  height and see how high it bounces.Drop the
  basketball from the same height and see how high
  it bounces.Put the tennis ball on top of the
  basketball and drop them both at arms length from
  waist height.
•  Results ExplanationThe tennis ball should
  bounce a lot higher than before. When the balls
  hit the ground, momentum from the basketball was
  transferred to the tennis ball making it go much
  higher than before.

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