Download 4.2 Gravity - Trimble County Schools

4.2b Notes
Objectives
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Explain why objects that are thrown follow a
curved path.
Compare circular motion with motion in a
straight line.
Projectile Motion
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Thrown objects don’t travel in straight lines,
they curve downward because of gravity
http://img.sparknotes.com/content/testprep/bookimgs/sat2/physics/0012/projectile.gif
Horizontal & Vertical Motion
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When you throw a ball, your hand exerts a
force pushing the ball forward
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Gravity accelerates the ball downward
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Horizontal motion
Vertical motion
Gravity exerts unbalanced force on the ball
Changes direction of ball from simply forward to
forward & down
 Ball appears to travel in a curve
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Throwing and dropping a ball from
the same height
• Both travel in same
vertical distance
• Thrown ball travels
more horizontal
distance
Click image to view movie
Centripetal Acceleration
• Acceleration
toward the
center of a
curved or circular
path
Centripetal Force
• Object entering a curve
• Speed doesn’t change
• Acceleration does change because direction
changes
• Object going around a curve
• Change of direction/velocity is toward center of
curve
Centripetal Force
• The net force exerted toward the center of a
curved path
• According to the second law of motion, when
an object has centripetal acceleration, the
direction of the net force on the object must
be toward the center of the curved path
Centripetal Force & Traction
• If a car is traveling around a curve,
centripetal force must be acting on the car
to keep it moving in a curved path
• This centripetal force is the frictional force, or
the traction, between the tires and the road
surface
Centripetal Force & Traction
• Anything that moves in a circle is doing so
because a centripetal force is accelerating it
toward the center
Gravity = Centripetal Force
• When whirling an object tied to a string above your head,
the string exerts a centripetal force on the object that keeps
it moving in a circular path.
• In the same way, Earth’s gravity exerts a
centripetal force on the Moon that keeps it
moving in a nearly circular orbit.
In-Class Assignment
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4.2 Reinforcement WKT