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Question: Rockets
If there were no launch pad beneath the space shuttle at lift-off, the upward thrust of its engines would be approximately unchanged. approximately half as much. approximately zero.
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Observations About Rockets
Plumes of flame emerge from rockets Rockets can accelerate straight up Rockets can go very fast The flame only touches the ground initially Rockets operate fine in empty space Rockets usually fly nose-first
Momentum Conservation
A rockets momentum is initially zero The momentum redistributes during thrust
Ship pushes on fuel; fuel pushes on ship Fuel acquires backward momentum Ship acquires forward momentum
Rockets total momentum remains zero
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Rocket Propulsion
Neglecting gravity, then
rockets total momentum is always zero momentum fuel + momentumship = 0
Question:
If there were no launch pad beneath the space shuttle at lift-off, the upward thrust of its engines would be approximately unchanged. approximately half as much. approximately zero.
The momentum of the ship depends on
the momentum of the ejected fuel, or the speed of that fuel and the mass of that fuel
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Rocket Engines
Chemical reactions produce hot, highpressure gas Gas speeds up in nozzle Gas reaches sonic speed in throat of de Laval nozzle Beyond throat, supersonic gas expands to speed up further
Stability and Orientation
On ground, rocket needs static stability In air, rocket needs aerodynamic stability
Center of dynamic pressure behind c.o.m.
In space, rocket is a freely rotating object
Orientation governed by angular momentum Rocket can in travel any orientation
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Ships Ultimate Speed
Increases as
ratio of fuel mass to ship mass increases fuel exhaust speed increases
Gravity Part 1
The earths acceleration due to gravity is only constant for small changes in height When the distance between two objects changes substantially, the relationship is:
force = gravitational constant mass1 mass 2 (distance between masses) 2
If fuel were released with rocket at rest,
speed ultimate =
Because rocket accelerates during thrust, ultimate speed is less than given above
massfuel speed exhaust massship
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Gravity Part 2
An objects weight is only constant for small changes in height When its height changes significantly, the relationship is:
gravitational constant object earth weight = (distance between centers of object and earth) 2
Gravity Part 3
An object high above the earth still weighs Astronauts and satellites have weights
weights are somewhat less than normal weights depen...