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Rockets

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Tamara Rajecki

on 14 July 2017

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Transcript of Rockets

ROCKETS
A vehicle, typically cylindrical, containing liquid or solid propellants which produce hot gases or ions that are forced down through a nozzle. This creates an action force accompanied by an opposite and equal reaction force, driving the vehicle upward. Rockets are self-contained, because they are able to operate in outer space.
Newtons' 3 Laws of Motion
1. Objects at rest will remain at rest and objects in motion will remain in motion in a straight line unless acted upon by an unbalanced force.
2. Force equals mass times acceleration.
3. Every action has an equal and opposite reaction.

1. Objects at Rest or in Motion
At Rest
:
forces are balanced. The force of gravity on the rocket balances with that of the launch pad holding it up.

In Motion
:
Thrust from the rocket unbalances the forces. As a result, the rocket travels upward (until it runs out of fuel).
2. F=mA
The pressure created inside the rocket produces force (thrust). Mass represents the total mass of the rocket, including its fuel.

The mass of the rocket changes during flight. As fuel is rapidly used and expelled, the rocket weighs less and accelerates.

Thrust continues until the engine stops firing.

3. Action and Reaction
A rocket takes off only when it expels gas.
Action: the rocket pushes the gas out of the engine.
Reaction: the gas pushes up on the rocket.

The Action (Thrust) has to be greater than the weight of the rocket for the Reaction (liftoff) to happen.
Inertia
Inertia is the resistance of an object to change its motion. It is associated with the mass of the object.
More mass = more inertia
Center of Mass
Center of mass is the exact point, which all of the mass of an object is perfectly balanced.
Center of Pressure
Center of pressure is the location where all the pressure acting on the rocket, both inside and out, are balanced.
The CP exists only when the rocket is moving.
DRAG
DRAG = Air resistance
Air resistance causes friction which slows down the rocket.
Friction always works in the opposite direction of the rocket's motion.
Even when a rocket is descending drag counteracts the rocket's motion.
Reducing Drag
AERODYNAMICS
Pointed Nose Cone - causes the air to part







Thinner, streamlined fins moved toward the tail end of the rocket.
Stability
How can you increase rocket stability?
1. Lengthen the rocket
2. Add mass to the nose cone. This is called ballast.
3. Extend the fins toward the end of the rocket.
4. Heavier rockets have more inertia and therefore are more stable.

(Don't add too much mass!)
BALLAST
Ballast is any mass added to a vehicle to improve stability and increase inertia.
Stability - ballast towards the nose cone will shift the center of mass forward.
Inertia - more ballast increases inertia and will prevent the rocket's path of motion from being prematurely overcome by drag.
Rocket Fin Shapes
Square/Trapezoidal = more stability and more drag
Triangular = less stability and less drag
TRAJECTORY
Trajectory is the curved path of an object traveling through space.
(Any object thrown or launched has trajectory.)
Boost Phase
inital period of thrust; ends when the fuel runs out.
Coast Phase
the period of flight when the rocket is not being actively powered; end of boost to ground impact
Apogee
highest point of trajectory
Multi-Stage Rockets
a rocket that uses two or more stages, each of which contains its own engine or propellant.
Advantages
By dropping each stage as it exhausts its fuel, it lightens the rocket, and provides more acceleration than the stage before.
Each stage can be built specific to the conditions of where the rocket is flying during that stage.
(The lower stage can be built to withstand the atmospheric pressure. Upper stage can withstand the vacuum of space.)
Disadvantages
Makes the rocket heavier and more difficult to build.
There is the potential for separation or ignition failure, or stage collision.
Costly to build.
First Stage (Stage 0) is associated with liftoff. 2nd and upper stages burn and fall off in order (called staging).
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