Falling Objects: Page 88

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Falling Objects Page
88 QUESTION Does a falling object
accelerate all the way down? OBJECTIVE
Students will be able to explain how falling
objects accelerate and why they reach terminal
velocity. VOCABULARY air resistance
terminal velocity projectile
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• Falling Objects
• Write these questions onto page 88
• SKIP ONE LINE BETWEEN EACH QUESTION
• Do all objects fall at the same speed?
• What is air resistance?
• When does an object reach terminal velocity?
• Does a projectile fall slower than a dropped
  object?

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How hard does the Earth pull on objects?
The Earths gravity pulls on all objects exactly
the same.
The acceleration due to the gravity of the Earth
(g) is 9.8 meters per second every second.
So all objects should fall at the same speed.
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Do all objects fall at the same speed?
What do you think?
No, all objects dont fall at the same speed.
If gravity pulls on all objects exactly the same,
then why dont they all fall at the same speed?
Follow my instructions for the demonstration.
How do you explain the results?
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What is air resistance?
Air resistance is the fluid friction that pushes
upward on falling objects. Where is there no air
resistance?
Objects that are light and have a large surface
area have the most air resistance.
A leaf would have a lot of air resistance, a
bowling ball would have much less.
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Can we calculate how fast objects fall?
Its almost impossible to do this unless we
pretend that there is no air resistance.
Even in high school when you do these types of
problems you will pretend objects are falling in
a vacuum.
The equation for calculating the speed of a
falling object without air resistance is
speed acceleration due to gravity (g) time
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Sample Problem 1
speed acceleration due to gravity (g)
time s gt
What is the speed of a ball dropped from a cliff
after it has fallen for 4 seconds?
Speed 9.8 m/sec2 4 seconds Speed 39.2
meters/second
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Now You Try It
speed acceleration due to gravity (g)
time s gt
What is the speed of a skydiver after he has
fallen for 5 seconds?
Speed 9.8 m/sec2 5 seconds Speed 49
meters/second
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When do Objects Reach their terminal velocity?
Terminal velocity is the fastest speed an object
can fall.
Terminal velocity is reached when air resistance
pushing upward is equal to gravity pulling
downward.
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Do projectiles fall slower than dropped objects?
Projectiles fall at exactly the same speed as
dropped objects.
Watch the demonstration.
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Falling Objects page 88 Check that the answers
to these questions are in your notes.

• Do all objects fall at the same speed?
• What is air resistance?
• When does an object reach terminal velocity?
• Does a projectile fall slower than a dropped
  object?

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VOCABULARY
Air resistance- the upward fluid friction on a
falling object. Terminal velocity- the fastest
speed an object can fall. Projectile- an object
that is thrown.
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