Projectile and Satellite Motion

1
Projectile and Satellite Motion

• Physics 1010
• Dr. Don Franceschetti
• February 24, 2004

2
Review

• Q 7.3 Cite an example when a force is exerted on
  an object without doing any work on the object.
• Q. 7.7 How many watts of power are expended when
  a force of 1 N moves a book 2 m in a time
  interval of 1 s?

3
Review

• Q7.22, Can a machine multiply input force? Input
  distance? Input energy?
• Q7.33 If a moving object doubles its speed, how
  much more momentum does it have? How much more
  energy?

4
Review

• Ex7.2 Which requires more work to stopa light
  truck or a heavier one that has equal speed.
• Prob 7.2 A car moving at 50 km/h skids 15 m car
  skid with locked brakes at with locked brakes.
  How far will car skid at 150 km/h?

5
Review

• Q 8.8 What is rotational inertia, and how does
  it compare to inertia as studied in previous
  chapters?
• Q 8.9 Inertia depends on mass rotational inertia
  depends on mass and something else. What?
• Q 8.13 Why does bending your legs when running
  enable you to swing your legs to and fro more
  rapidly?

6
Review

• Q 8.32 How can gravity be simulated in an
  orbiting space station?
• Q 8.33 Why will orbiting space stations that
  simulate gravity likely be large structures?

7
Review

• Q 8.23 Why is the wobbly motion of a single star
  an indication that the star has one or more
  planets orbiting around it?
• Q8.24 Why must you bend forward when carrying a
  heavy load on your back?

8
Review

• Q 9.1 What was it that Newton discovered about
  gravity?
• Q 9.5 What is the magnitude of the gravitational
  force between two 1-kg bodies that are one meter
  apart.
• Q 9.6 What is the magnitude of the gravitational
  force between the Earth and a 1-kg body.

9
Review

• Ex 9.1 Gravitational force acts on all bodies in
  proportion to their masses. Why, then, doesnt a
  heavy body fall faster than a light body.
• Ex 9.10 Somewhere between the Earth and the moon,
  gravity from these two bodies on a space pod
  would cancel. Is this location nearer the Earth
  or moon?

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Projectiles

• A projectile is any object that is projected by
  some means and continues in motion by its own
  inertia.
• Main classes are weapons bullets, arrows,
  artillery shells, bombs, rocks and balls
  baseballs, footballs, golf balls

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Projectiles

• Are in free fall, neglecting air resistance
• The horizontal component of velocity does not
  change because the net force acting has zero
  horizontal component
• The vertical component changes in response to the
  gravitational force.

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Projectile motion by superposition

• Projectiles launched horizontally
• Upwardly launched projectiles
• Range is same for angle and complementary angle.
• Greatest range for projectiles launched at 45
  degrees.

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Fast moving projectiles satellites

• Circular orbits
• Near earth 90 minute period
• Orbital sped 8km/s, near Earths surface
• Geosynchronous, 24 hour period, orbital speed is
  less
• Elliptic orbits
• Keplers laws apply

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Energy Conservation and Satellite Motion

• Terminology
• Apogee, most distant point from Earth
• Potential energy is greatest
• Kinetic energy is least, motion is slowest
• Perigee, closest approach to Earth
• Potential energy is least
• Kinetic energy is greatest, speed is hight
• Perihelion, aphelion, apply to planet and Sun

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Escape speed

• Minimum speed needed to escape planet
• from Earth is 11.2 km/s.
• From Sun at Earth orbit is 42.2 km/s
• Pioneer 10 left Earth in 1972 at 15km/s used
  gravitational assist from Jupiter.

16
Review

• Q10.5 A rock is thrown upward at an angle. What
  happens to the horizontal component of its
  velocity as it rises? As it falls?
• Q10.6 A rock is thrown upward at an angle. What
  happens to the vertical component of its velocity
  as it rises? As it falls?

17
Review

• Q 10.14 Are the planets of the solar system
  simply projectiles falling around the sun?
• Q 10.18 Why does the force of gravity change the
  speed of a satellite in an elliptical orbit.

18
Review

• Q10.25 Why is the kinetic energy a constant for
  a satellite in circular orbit?
• Q 10.26 Why is kinetic energy a variable for a
  satellite in an elliptical orbit?

19
Review

• E10.4 In the absence of air drag, why does the
  horizontal component of a projectiles motion not
  change, while the vertical component does?
• E10.9 When a rifle is being fired at a distant
  target, why isnt the barrel lined up so that it
  points exactly at the target?

20
Review

• E10.15 Since the moon is gravitationally
  attracted to earth, why does it not simply crash
  into the Earth?
• E10.16 When the space shuttle coasts in a
  circular orbit at constant speed about the Earth,
  is it accelerating? If so, in what direction? If
  not, why not?

21
Review

• E10.18 Does the speed of a falling object depend
  on its mass? Does the speed of a satellite in
  orbit depend on its mass?