Projectiles,SATELLITES and Orbit

1
Projectiles,SATELLITES and Orbit

• Satellite and Circular Motion
• The path of an orbiting satellite follows the
  curvature of the Earth.

2
Projectile Defined

• Any launched object that moves through air or
  space under the influence of gravity.

3
Horizontal Motion Associated with a Projectile

• Objects launched horizontally continue in a
  horizontal direction a constant speed due to its
  inertia.

4
Vertical Motion Associated with a Projectile

• Objects motion is accelerated due to the force
  of gravity (free falling!!)

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Projectile Motion Review
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How would you describe the downward motion of the
two balls?
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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.

8
Horizontal vs. Vertical Motion for Satellites
tangential velocity (or rotational velocity)
gravity
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
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Projectile Path Principles

• The greater the objects 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.
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Figure 4
b
a
1) Label the arrows as gravity or sideways
velocity. Place term inside box.

• Which arrow represents centripetal force?
• 3) What would happen to the moon if the Earths
  gravity suddenly disappeared?

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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)
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The Earth Curves
A horizontal speed of 8 km/s will cause the
projectile to become a satellite.
13
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.
14
Satellites Path

• The shape of the path of a satellite is circular
  or elliptical (oval).

An ellipse is a closed oval-shaped path. The
Earth orbits the Sun in an ellipse!
15
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

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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

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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.

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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.

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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/chapter
  4/chapter4.html

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References

• http//www-istp.gsfc.nasa.gov/stargaze/Skeplaws.ht
  m

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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.

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References

• http//www-istp.gsfc.nasa.gov/stargaze/Skeplaws.ht
  m