Transcript document

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Chapter 13 Section 1b
The Science of Rockets
How does a rocket work?
What is the main advantage of a
multistage rocket?
Newton’s 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
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)
Action-Reaction Pair
Action on
the wall
motion
Reaction on
the skater
• When a skateboarder
pushes against a wall
(action force)
• The wall pushes the
skater in the opposite
direction (reaction
force)
How Do Rockets Work?
• A rocket moves forward when gases
shooting out the back of the rocket push
it in the opposite direction.
Escaping Earth’s Gravity
• In order for a rocket to move out of Earth’s
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 greater:orbital velocity or
escape velocity?
• How can scientists calculate the needed
thrust to achieve the correct velocities?
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. F=ma
• To calculate the amount of thrust needed
scientists use Newton’s second law.
Force (thrust) = mass x acceleration
Rocket Fuels
• Three types of rocket
fuel are used
– Solid fuel (fuel +
oxidizer)
– Liquid fuel (fuel +
oxygen)
– Electrically charged gas
(ions)
Rocket Altitude
•A rocket’s altitude is
how high it is above
the ground. Use the
graph to answer the
following questions
about how a model
rocket’s altitude
changes over time.
Rocket Altitude
• Reading Graphs:
– What two variables
are being graphed? In
what unit is each
measured?
–Altitude and time,
meters and seconds
Rocket Altitude
• Reading Graphs:
– What was the rocket’s
altitude after 2
seconds? After 4
seconds?
–About 65 meters; about
128 meters
Rocket Altitude
• Reading Graphs:
– At what time did the
rocket reach its
greatest altitude?
–6 seconds
Rocket Altitude
• Inferring:
– Why do you think the
rocket continued to rise
after it ran out of fuel?
–The rocket’s 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
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.
End of Section:
The Science of Rockets