Physics 135A

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Physics 135A

• Physics 135A
• Lecture 11 Midterm 1 Review Session
• Dr. Z. Gong

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Physics 135A
Administrative Information

• Homework Set 5 due on Thursday
• First Midterm on Wednesday Oct. 2 in THH 101 from
  5 630pm
• Midterm coverage Ch 1 5
• Sample midterms available on the web

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Physics 135A
Ch. 1

• Uncertainty
• Estimate uncertainty absolute uncertainty
• How to estimate?
• Measurement x ?x
• Percent uncertainty relative uncertainty
• percent uncertainty

xmax
x
xmin
?x
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Physics 135A
Ch. 1

• Error propagation
• If we know the quantities and their accuracy
• A ?A, B ?B and C ?C, then
• D A B C
• E A B / C
• F An

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Physics 135A
Physics 135A
Ch. 1

• Significant figures
• For Multiplication and Division, the number of
  significant figures in the final result should be
  no more than the least number of significant
  figures used in the calculation.
• For Addition and Subtraction, the result should
  have the same accuracy as the least accurate
  term(s) used in the calculation.
• For any exact numbers and parameters by
  definition there are infinite number of
  significant figures.

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Physics 135A
Physics 135A
Ch. 1
Example If a block has length l 10.36 cm,
width w 7.81 cm and height h 8.3102 mm. What
is the volume of the block?
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Physics 135A
Ch. 1

• Unit and unit conversion
• The standard unit is meter for length, kilogram
  for mass and second for time.
• Example 65 mph ? m/s

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Physics 135A
Ch. 2

• Displacement vs. Distance
• Displacement is vector from the starting point
  to the end point, with magnitude and direction
• Distance is scalar add all the path traveled,
  with magnitude only
• Velocity vs. Speed
• Velocity is vector
• Speed is scalar

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Physics 135A
Ch. 2

• Instantaneous velocity
• Acceleration

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Physics 135A
Ch. 2

• Motion at constant acceleration
• Quadratic equation

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Physics 135A
Ch. 2

• Example
• A falling stone takes 0.30s to travel past a
  window 2.2m tall. From what height above the top
  of the window did the stone fall?

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Physics 135A
Ch. 3

• Vector Addition
• Tail to tip
• Parallelogram

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Physics 135A
Ch. 3

• Vector Addition
• Add components

?
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Physics 135A
Ch. 3

• Trigonometry

h
y
?
x
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Physics 135A
Ch. 3

• Projectile motion
• The projected horizontal motion and vertical
  motion are independent except that they share the
  same time tAx tAy at any instance.

t1
t2
t3
t4
t0
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Physics 135A
Ch. 3

• General equations
• If ax 0, ay -g -9.80m/s2

x component
y component
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Physics 135A
Ch. 3
Example An athlete executing a long jump
leaves the ground at 30o angle and travels 7.80
m. What was the take off speed? If the speed is
increased by 5, how much longer will the jump go?
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Physics 135A
Ch. 3

• Relative motion
• If we denote the relative velocity of object A
  with respect to reference frame B as then

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Physics 135A
Ch. 3
Example A boat, whose speed in still water is
2.2m/s, must across a 260 m wide river and arrive
at a point 110 m upstream from where it starts.
To do so, the pilot must head the boat at a 45o
upstream angle. What is the speed of the rivers
current?
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Physics 135A
Ch. 4

• Newtons 1st law of motion Every body continues
  in its state of rest or of uniform speed in a
  straight line (due to inertia) unless acted on by
  a nonzero net force.
• Newtons 2nd law of motion The acceleration of
  an object is proportional to the net force on it
  and inversely proportional to its mass.
• Newtons 3rd law of motion Whenever one object
  exerts a force on a second object, the second
  object exerts an equal and opposite force on the
  first one

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Physics 135A
Ch. 4

• Newtons 2nd law of motion
• The direction of acceleration is the same as the
  net force acting on it.
• This law applies to each projected component

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Physics 135A
Ch. 4

• Free body diagram
• Draw each object separately
• Get x and y components of all the forces to
  calculate the net force
• Apply Newtons second law to get acceleration
• Apply the acceleration to solve any motion
  related problems

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Physics 135A
Ch. 4
Example The two masses shown below are each
initially 1.80m above the ground, and the
massless pulley is 4.80m above the ground. What
maximum height does the lighter object reach
after the system is released?
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Physics 135A
Ch. 4

• Friction
• Static friction force parallel to the surface
  of contact when there is no relative motion
• Static friction force can vary from zero to
  maximum static friction
• Kinetic friction parallel to the surface of
  contact when there is relative motion
• Kinetic friction force is always the same

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Physics 135A
Ch. 4
Example A child slides down a slide with a 28o
incline, and at the bottom her speed is precisely
half what it would have been if the slide had
been frictionless. Calculate the coefficient of
kinetic friction between the slide and the child.
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Physics 135A
Ch. 5

• Uniform circular motion
• Period T the time it takes to revolve a circle
• Frequency f number of revolutions per second

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Physics 135A
Ch. 5

• Centripetal acceleration
• Centripetal force
• The centripetal force is pointing to the center
  of the circle.

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Physics 135A
Ch. 5

• Example
• A jet pilot takes his aircraft in a vertical
  loop. If the jet is moving at a speed of 1500
  km/h at the lowest point of the loop, whats the
  minimum radius so that the centripetal
  acceleration at that point does not exceed 6.0g?
  Calculate the effective weight of the 80 kg pilot
  at the bottom and top of the loop.

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Physics 135A
Ch. 5

• Newtons law of gravitation
• Every particle attracts the other particles. The
  force between two particles can be expressed as
• where m1 and m2 are mass of the two particles, r
  is the distance between them, and G6.6710-11
  Nm2/kg2 is the gravitational constant.

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Physics 135A
Ch. 5

• Apparent weight is measured by a scale attaching
  to an object. If there is vertical acceleration
  acting on that object the apparent weight w can
  be different from the actual weight mg
• Keplers law For any two planets the period and
  the mean radius to the sun has such relationship