Homework for Chapter 1

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Homework for Chapter 1
The time it takes a planet to make one complete
trip around the sun is called the planet's

• Orbit
• Revolution
• Rotation
• Period

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Homework for Chapter 1
The ptolemaic system fulfilled the requirements
of a scientific theory because

• its explanations of celestial motions, based on
  observations, resulted in testable predictions
• it was presented openly for public inspection
  when included in Ptolemy's Almagest
• it was believed to represent an accurate view of
  the universe and solar system by religious
  leaders and learned scholars of the time
• it provided a "common sense" explanation
  concerning the observed motions of heavenly
  bodies

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Lecture 3MotionAcceleration of Gravity
Chapter 2.1 ? 2.6
Outline

• Describing motion (speed and velocity)
• Acceleration
• Acceleration of gravity

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Speed, Distance, and Time

• Speed is a rate of covering distance

distance Speed ??????
time
? Average speed
d distance
t time
v speed
vd/t or dv x t or td/v
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Units
Everything measurable is measured in standard
quantities called units.
In science, the International System (SI) of
units is used.
The main SI units are meter (m) for
length second (s) for time kilogram (kg) for
mass joule (j) for energy watt (w) for power
Some useful relations 1 m 100 cm 3.28 feet 1
km 0.62 mi 1 cm 0.39 inch 1 kg 1000 g 2.2
lbs 1 lbs 453 g
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Units
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Simple Problems with Unit Conversion
How many inches are in 1 km?
100000 cm/2.54 39370 in
How far is New York from Toledo in km (600 mi)?
1 km 0.62 mi, 1mi1.61km 600 mi 600x1.611000
km
How heavy is a 150 lbs person in kg?
1 lbs 0.453 kg 150 lbs x 0.453 68 kg
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Vectors
Quantities, which can be described by only a
number, are called scalar quantities.
Quantities, which are also characterized by
direction, are called vector quantities.
Speed is a scalar, while Velocity is a vector.
Addition of vectors
Vector
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Acceleration
Acceleration (a) is a change in velocity and is a
vector.
vi ? initial speed vf ? final speed T ? time
interval
vf ? vi a ????? t
Units of acceleration are meters per second per
second or meters per second squared (m/s2).
Demonstration of acceleration
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Sir Isaac Newton (1642-1727)
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The Universal Law of Gravitation
gravity
Every mass attracts every other mass through
the force called gravity The force of attraction
is directly proportional to the product of their
masses The force of attraction is inversely
proportional to the distance between the objects
Fg G x M1x M2 / d2
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Acceleration of Gravity
From our experience, we know that everything
falls down. Galileo found that the higher the
object when it is dropped, the greater its speed
at the ground.
It was also found that the acceleration of
falling objects is independent of their mass
(neglecting air resistance).
Acceleration of gravity g 9.8 m/s2
If something is dropped from rest, its downward
speed will be v gt.
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Acceleration of Gravity
The downward acceleration g is the same, no
matter where an object is thrown.
If an object is thrown upward at an angle, it
will come to the ground on a curved path called a
parabola.
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Calculating speeds, distances, and times for
falling objects
If a dropped object initially at rest, its speed
v after some time t is v g x t gt. If there
was an initial speed v0, then v v0gt.
Distance, which an object travels during time t,
is then d v0tgt2/2
Time, during which a resting object will reach
the ground, is t ?(2d/g)
Example you will fall off the 3-m UT Rec dive
board for 0.8 s.
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Summary

• Motion can be described with both scalar and
  vector quantities.

• Speed is a scalar, velocity is a vector.

• Acceleration is a rate of changing velocity.

• Acceleration of gravity is the same for an object
  of any mass.