Chapter 13 Section 1b: The Science of Rockets

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Chapter 13 Section 1bThe Science of Rockets

• How does a rocket work?
• What is the main advantage of a multistage rocket?

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Newtons Third Law of Motion

• If one object exerts a force on another object
• then the second object exerts a force of equal
  strength in the opposite direction on the first
  object.

Ball
Head
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Action-Reaction Pair

• When the dog leaps, it pushes down on the ground
  (action force)
• The ground pushes the dog into the air (reaction
  force)

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Action-Reaction Pair
Action on the wall

• When a skateboarder pushes against a wall (action
  force)
• The wall pushes the skater in the opposite
  direction (reaction force)

motion
Reaction on the skater
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How Do Rockets Work?

• A rocket moves forward when gases shooting out
  the back of the rocket push it in the opposite
  direction.

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Escaping Earths Gravity

• In order for a rocket to move out of Earths
  gravity it must achieve a certain velocity called
  escape velocity.
• In order for a rocket to go into orbit around the
  Earth it must achieve orbital velocity.
• Which must be greaterorbital velocity or escape
  velocity?
• How can scientists calculate the needed thrust to
  achieve the correct velocities?

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Thrust

• Thrust is the reaction force that propels the
  rocket forward.
• Thrust depends on the mass of the gases and the
  speed of the gases coming out the rocket engine.
  Fma
• To calculate the amount of thrust needed
  scientists use Newtons second law.
• Force (thrust) mass x acceleration

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Rocket Fuels

• Three types of rocket fuel are used
• Solid fuel (fuel oxidizer)
• Liquid fuel (fuel oxygen)
• Electrically charged gas (ions)

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Rocket Altitude

• A rockets altitude is how high it is above the
  ground. Use the graph to answer the following
  questions about how a model rockets altitude
  changes over time.

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Rocket Altitude

• Reading Graphs
• What two variables are being graphed? In what
  unit is each measured?

• Altitude and time, meters and seconds

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Rocket Altitude

• Reading Graphs
• What was the rockets altitude after 2 seconds?
  After 4 seconds?

• About 65 meters about 128 meters

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Rocket Altitude

• Reading Graphs
• At what time did the rocket reach its greatest
  altitude?

• 6 seconds

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Rocket Altitude

• Inferring
• Why do you think the rocket continued to rise
  after it ran out of fuel?

• The rockets inertia caused it to continue to
  rise after its fuel ran out. Eventually friction
  caused the rocket to slow down and gravity caused
  it to fall

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A Multistage Rocket

• A typical multistage rocket has three stages.
  Each of the first two stages burns all of its
  fuel and then drops off. The next stage then
  takes over.

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End of SectionThe Science of Rockets