REFERENCE POINT

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REFERENCE POINT
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REFERENCE POINT

• What is your speed right now?
• In reference to the chair? 0 m/s
• In reference to the earth? 1000 mi/s

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REFERENCE POINT

• If I drop a tennis ball, what does it do?
• In reference to the ground, it drops straight
  down.
• In reference to the earth, it has moved hundreds
  or thousands of feet by the time it hits the
  ground because the earth is spinning so fast.

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REFERENCE POINT
The earth spins 1000 mi/s. It takes a few
seconds for the ball to hit the ground. So, the
ball is hitting the ground thousands of miles
from where it was dropped.
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REFERENCE POINT

• If I am riding inside a car, and I throw a ball
  straight up in the air, what happens?

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REFERENCE POINT

• What does it look like to you?
• It falls straight down.
• What would it look like to someone standing
  outside the car? (Imagine everything but the
  ball is invisible)
• It would hit the ground a short distance from
  where the ball was dropped.

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REFERENCE POINT
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REFERENCE POINT

• Definition
• A reference point is something that we use to
  compare the speed of other things to.

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REFERENCE POINT

• 1. Two objects heading in opposite directions
  (either toward or away from each other). To find
  their speeds in reference to each other add the
  two speeds together.

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REFERENCE POINT

• Example Head-on Collision

10 mi/hr
12 mi/hr
These two cars will collide at 22 mi/hr (10 12)
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REFERENCE POINT

• Example Moving away from each other

8 mi/hr
9 mi/hr
These two cars are moving away from each other at
a speed of 17 mi/hr.
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REFERENCE POINT

• 2. Something that is moving while riding on
  something else and the reference point is on the
  bigger object. For example, if a ball was thrown
  inside the back of a truck

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REFERENCE POINT

• a. If a truck has a steady velocity, then the
  balls motion will be unaffected by the trucks
  velocity.
• b. If the truck is changing its velocity, then
  the balls motion will be changed or appearing to
  change.

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REFERENCE POINT

• For example, if the truck was turning, the ball
  would appear to curve if you were inside the back
  of the truck and threw the ball.
• (x person o ball)

Truck starting to Turn ball appears to start to
curve as the truck turns
Turning ball appears to curve as truck is
definitely turning
Steady Velocity ball move straight and is
unaffected by the trucks velocity
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REFERENCE POINT

• 3. Something that is moving while riding on
  something else, but the reference point is
  outside both objects. For example, a ball thrown
  from a car.

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REFERENCE POINT

• a. If both objects are going in the same
  direction, then add the two speeds together.

Speed of the ball being thrown 45 mi/hr Speed
of the car 55 mi/hr
He will catch it at a speed of 100 mi/hr (45
55)
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REFERENCE POINT

• b.If the objects are going in opposite
  directions, then forward is positive, backward is
  negative and add the 2 speeds.

The car is moving forwards at a speed of 55 mi/hr
The ball is moving backwards at a speed of 45
mi/hr
He will catch it at a speed of 10 mi/hr (55)
(-45)