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Projectiles,SATELLITES and
Orbit
Satellite and Circular Motion
The path of an orbiting satellite
follows the curvature of the
Earth.
Projectile Defined
• Any launched object that moves through air or
space under the influence of gravity.
Horizontal Motion Associated with
a Projectile
• Objects launched horizontally continue in a
horizontal direction a constant speed due to
its inertia.
Vertical Motion Associated with a
Projectile
• Object’s motion is accelerated due to the force of
gravity (free falling!!)
Projectile Motion Review
How would you describe the
downward motion of the two balls?
What is an Earth Satellite?
• A projectile that circles the Earth due to
gravitational force.
• Orbit occurs because the object moves
fast enough to fall continuously towards
the Earth and miss it.
Horizontal vs. Vertical Motion for
Satellites
tangential velocity
gravity
(or rotational
velocity)
Note the curved projectile
path!
There is a balance between the tangential speed
of the projectile and the force of gravity acting
on the projectile
Projectile Path Principles
• The greater the object’s horizontal motion
(or speed), the wider the arc of its curved
path.
• If thrown from the same height, both
projectiles will land at the same time even
if their horizontal speeds are different.
See Figures 14.1 and 14.3 on page 263.
Figure 4
b
a
1) Label the arrows as gravity or
sideways velocity. Place term inside
box.
2)
Which arrow represents centripetal force?
3)
What would happen to the moon if the Earth’s gravity suddenly
disappeared?
Horizontal vs. Vertical Motion
Orbital velocity
gravity
There is a balance between the orbital velocity of the projectile
and the force of gravity pulling on the projectile (as the projectile
pulls on the Earth)
The Earth Curves
A horizontal speed of 8 km/s will
cause the projectile to become a
satellite.
Circular Orbits
• A projectile with a speed of 8 km/s will
orbit the Earth in a circle.
A satellite in circular orbit is always
moving perpendicular to gravity.
Satellite’s Path
• The shape of the path of a satellite is
circular or elliptical (oval).
An ellipse is a
closed ovalshaped path.
The Earth orbits
the Sun in an
ellipse!
Circular and Elliptical Orbits
• The cause for a projectile to orbit the Earth is the
horizontal speed of the projectile.
• Checking horizontal speed (tangential velocity)
-Less than 8 km/s: no orbit
-At 8 km/s: circular orbit develops
-Greater than 8 km/s: elliptical
orbit develops
Orbit
• A successful orbit occurs when the horizontal speed
balances the downward acceleration of gravity.
• The unbalanced force caused by gravity provides the
change in velocity needed to keep the satellite turning.
• Checking horizontal speed (tangential velocity)
-Less than 8 km/s: no orbit
-At 8 km/s: circular orbit develops
-Greater than 8 km/s: elliptical
orbit develops
-escape velocity at 11.2 km/s
Escape Speed
• A vertical speed that is sufficient to ensure
that the object will leave the Earth or
whatever object from which the projectile
is launched.
CENTRIPETAL FORCE
• The force that keeps an object going in a
circle (means “toward center”).
• Gravity, friction and pulling on a cord are
examples of centripetal force.
• You feel a push away from the center
because of your inertia.
• It takes a force to change your
momentum.
Centripetal Motion Applications
• http://www.glenbrook.k12.il.us/gbssci/phys
/mmedia/circmot/cf.html
• http://www.glenbrook.k12.il.us/gbssci/phys
/mmedia/vectors/sat.html
• http://sol.sci.uop.edu/~jfalward/physics17/
chapter4/chapter4.html
References
• http://wwwistp.gsfc.nasa.gov/stargaze/Skeplaws.htm
The Speed of Projectiles and
Satellites
• For projectiles and satellites, the speed of
the object is related to differences in the
two components of motion.
References
• http://wwwistp.gsfc.nasa.gov/stargaze/Skeplaws.htm