Mav Mark 10/17/11

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Mav Mark10/17/11

• At which point in this diagram is the field the
  strongest?

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Mav Mark10/18/11

• About how fast does Earth rotate? Remember,
  circumference 24,000 miles.

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Mav Mark10/19/20

• Which modern theory gave an explanation for
  Newton's spontaneous gravitational attractions?

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Mav Mark10/20/11

• Place the following terms in order of electrical
  transmission from plant to lamp lamp, step up
  transformer, step down transformer, power
  substation, outlet?

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Motion Forces

• Notes

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Describing and Measuring Forces

• An object is said to be in motion if it changes
  position relative to a reference point.
• Motion means moving. To find out if an object is
  in motion, you MUST compare it to another object
  or place. This is known as relativity.
• An object is in motion if its distance from
  another object or place is changing.

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Describing and Measuring Forces

• A reference point is an object or place that you
  can use to tell if an object is in motion. A
  tree, a sign, or a building make good reference
  points.

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Describing and Measuring Forces

• Have you ever been in a bus or car sitting beside
  another one? Suddenly, you think that your
  vehicle is moving backward. Upon closer
  inspection, you actually find that its the other
  vehicle that is moving forward. Because you were
  using a moving object as a reference point, your
  sense of motion was inverted.
• Now, imagine astronomers when they saw the sun.
  Because they thought that Earth was the
  stationary reference point, they mistakenly
  thought that it was the universe that revolved,
  and not Earth.

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Describing and Measuring Motion

• Motion is measured as distance. A meter is a unit
  of length.
• This can be modified by adding a metric prefix
  such as kilo-, nano-, cent-, etc.
• 1mm .001 meters
• 1nm .000001 meters
• 1km 1000 meters

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Calculating Speed

• If you know the distance an object travels in a
  certain amount of time, you can calculate the
  speed of an object.
• Speed is a rate. It tells how far something
  moves in a certain amount of time. For example, 1
  meter per second is speed.

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Calculating Speed
D
D Distance
T Time
S
T
S Speed
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Calculating Speed

• On a car ride to school, you speed up and slow
  down.
• Average speed tells the total distance you rode
  divided by the total time it took.
• Instantaneous speed is the speed you were moving
  at an instant in time. during the car ride.

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Calculating Speed

• Suppose that a cyclist travels 32 kilometers in
  the first 2 hours of her trek. She then travels
  another 13 kilometers during the next hour.
• What is her average speed?

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Describing Velocity

• To completely describe the motion of an object,
  you need to not only know its speed, but also its
  direction.
• When you know both speed AND direction, then you
  can calculate velocity
• Velocity is speed in a given direction.

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Describing Velocity

• For example, you hear that a thunderstorm is
  traveling at 25 km/h. Should you fear for your
  life?
• Well, that depends on its direction of motion.
• If youre an air traffic controller, if you just
  give the speeds of the other planes to the
  pilots, then they still might crash into each
  other. The planes directions are vitally
  important.

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24 hours of United States Air Traffic
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What is a Force?

• Like velocity, force is described by its strength
  and by the direction in which it acts.
• A force is a push or pull.

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What is a Force?
YES
Not Quite
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What is a Force?

• To tell about a force, you must tell how strong
  the force is. The SI unit for strength of a force
  is the newton.
• To tell about a force, you must also tell the
  direction the force is pushing or pulling.
• Arrows can be used to show forces. The point of
  the arrow shows the direction of the force. The
  length of the arrow shows how strong the force is.

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Combining Forces

• Unbalanced forces acting on an object result in a
  net force and cause a change in the objects
  motion. Balanced forces acting on an object do
  not change the objects motion.
• Often there is more than once force acting on an
  object. The total of all the forces acting on an
  object is called the net force.

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Combining Forces

• Sometimes the net force on an object is 0. This
  means there are balanced forces acting on the
  object. The objects motion does not change.
• In space, this means it could be stationary, or
  its traveling at constant velocity.

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Combining Forces

• Sometimes, the net force does not equal 0. This
  means there are unbalanced forces acting on the
  object. The objects motion changes.
• In space, this means the object will curve, speed
  up, or slow down. In other words, its velocity
  will change.

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