Anthrax scare at the University of Arkansas

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Anthrax scare at the University of Arkansas

• Arkansas Razorbacks football practice was delayed
  nearly two hours today after a player reported
  finding an unknown white powdery substance on the
  practice field.Head Coach Houston Nutt
  immediately suspended practice while police
  andfederal investigators were called to
  investigate. After a complete analysis, FBI
  forensic experts determined that the white
  substance unknown to the players was the goal
  line.Practice was resumed after special agents
  decided the team was unlikely to encounter the
  substance again.

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Chapter 5- Matter in Motion

• Section 4- Gravity A Force of Attraction

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Objectives

• Define gravity
• State the law of universal gravitation
• Describe the difference between mass weight

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Think About.

• Why did the astronauts who walked on the moon in
  very heavy space suits bounce so easily when we
  really have to work hard to bounce a few
  centimeters off the ground?
• Gravity- A force of attraction between objects
  due to their masses

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All Matter is Affected by Gravity

• All matter has mass, gravity is a result of
  mass. Therefore, all matter experiences gravity
• Why do we not notice the effects of gravity?
• The mass of most objects is too small to cause an
  attraction large enough to move objects toward
  each other

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Earths Gravitational Force is Large

• Compared to other objects, Earth has an enormous
  mass.
• Therefore, the Earths gravitational force is
  very large
• You must apply enough force to overcome Earths
  force any time you lift an object or move your
  body

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The Law of Universal Gravitation

• The Core of an Idea
• Newton made the observation that when an apple
  falls from a tree, there has to be an unbalanced
  force affecting it. This unbalanced force is
  gravity

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A Law is Born

• Newton generalized his observations into the Law
  of Universal Gravitation
• Describes the relationships between gravitational
  force, mass, distance
• Called universal because it applies to all laws
  in the universe
• All objects in the universe attract each other
  through gravitational force. The size of the
  force depends on the mass of the objects the
  distance between them.
• Consider this law in 2 parts

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Figure 20, Page 127

• Gravitational force is small between objects with
  small masses

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Figure 20, Page 127

• Gravitational force is larger between objects
  with larger masses.

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Figure 20, Page 127

• If the distance between 2 objects is increased,
  the gravitational force pulling them together is
  reduced.

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Part 1 Gravitational Force Increases as Mass
Increases

• Imagine an elephant and a cat
• There is more gravity between the elephant and
  Earth than between the cat and Earth
• Thats why its easier to pick up a cat than it
  is to pick up an elephant
• There is gravity between the animals the Earth,
  but it is so much smaller than the mass of the
  Earth

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Part 2 Gravitational Force Decreases as Distance
Increases

• Why doesnt the suns gravitational force affect
  you more than Earths does?
• Because of the distance- we are 150 mil km.
  from the sun
• At this distance, the gravity between us and the
  sun is very small
• The suns gravity has an affect on the planets
• Figure 21, page 128

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Weight is a Measure of Gravitational Force

• Weight- A measure of gravitational force exerted
  on an object
• Typically, when people discuss weight, they mean
  Earths gravitational force. This can also refer
  to the gravitational force of the moon or other
  planets
• Weight is also expressed in newtons (N)
• 1 N 100g

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Weight Mass Are Different

• Weight mass are similar, but not the same
• Weight changes with gravitational force
• Mass- The amount of matter in an object
• Value does not change
• Figure 22, page 129

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Review

• How does mass relate to the gravitational force
  exerted on other objects?
• How does the distance between objects affect
  gravity?

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Assignment

• Explain Figure 22 on page 129.
• Due at the end of the period for a grade