Rockets Part 2: How Rockets Move

Rockets Part 2: How Rockets Move

By Abby Fancsali

Recap: Newton's Laws

• Issac Newton's three laws of motion are essential to how rockets work

  • Newton's 1st law: An object in motion will continue in motion and an object at rest will stay at rest​ until acted upon by a force

    • Law of Inertia

  • Newton's 2nd law: The force of an object is equal to the mass multiplied by the acceleration

  • Newton's 3rd law: Every action has an equal and opposite reaction

What makes a Rocket a Rocket?

• A Rocket is any device that burns some form of fuel, causing extremely hot gases to be expelled from one end

  • Fuel can be solid or liquid

    • Earliest Rockets used steam as fuels

  • As the Fuel leaves the tail end of the rocket, the force from the expulsion pushes the rocket forward​

Launching a Rocket

• In Liquid fuel rockets the fuel is pumped into a combustion chamber with a liquid oxidizer

  • At launch, an ignition ​system provides a spark that causes the mixture to explode

• As the gas is expelled downward, the explosion propels the rocket up

  • Thrust: The downward force that pushes a rocket upwards​

    • In order to launch, thrust must be greater than gravity

Launching a Rocket

• Solid Fueled rockets are much simpler than liquid fuel rockets

  • only need on tank and a combustion chamber

    • Can't be stopped once ignited​

  • Much less efficient than a liquid fuel rocket

    • Mainly used as boosters to liquid fuel rockets

Multiple Choice

According to Newton's Third lawWhen a rocket is launched, which is the action?

• The expulsion of the burning fuel

• The rocket moving upwards

Multiple Choice

According to Newton's Third lawWhen a rocket is launched, which is the reaction?

• The expulsion of the burning fuel

• The rocket moving upwards

Why can't an airplan fly in space

• Airplanes are built to move by pushing air out of the way.

• Since space is a vacuum, there is no air to push and the plane would just fall

Moving and Landing a Rocket

• Weight: the force of gravity acting on the mass of an object

  • Weight has to be overcome by thrust in order to move

  • Needs to be equally balanced

  • Too much weight makes it hard to move in any direction

• Control: The ability to move a rocket in the right direction

  • Requires balancing weight and thrust​

  • Fins help provide control against air resistance

• Drag: The resistance of air that works against an object

  • Slows an object down

  • Once a rocket leaves the atmosphere, there is no air to provide drag so the rocket can move much more efficiently​

Multiple Choice

Which object experiences the most drag when falling

• a flat sheet of paper

• a marble

• a crumpled sheet of paper

• a pencil

Multiple Choice

Think about it: If you have a hose and want the maximum amount of water pressure, what sort of nozzle should you use?

• A wide mouthed nozzle

• A narrow Nozzle

• The Nozzle doesn't matter

Improving Thrust

• In order to get the most thrust out of a slow moving rocket, the fuel exit needs to be as narrow as possible

  • pressure = force/area

    • Smaller area gives more pressure to work with​

• A fast moving rocket has a wider fuel exit because the fuel is compressed so tightly that once ignited, it already releases at a greater force

  • As the plume leaves the rocket, and enters the high pressure of space, a wide bell allows it to spread out ​and provide more thrust

Improving Control

• Fins help provide control to a rocket after launch

  • Stop it from Wobbling in the air due to resistance​

  • Need to provide control without bringing too much drag on the rocket

• The Center of Gravity and Center of Pressure of the rocket needs to be precise

  • Center of Gravity: Point where weight is evenly distributed on both sides of the rocket

  • Center of Pressure: Point where Surface area is evenly distributed on both sides of the Rocket​

  • If the two are too close or on top of each other, the rocket will start to spin

Multiple Choice

This is The resistance of air that works against an object

• Drag

• Thrust

• Control

• Weight

• Center of Gravity

Multiple Choice

This is The force that acts against gravity in an object

• Drag

• Thrust

• Control

• Weight

• Center of Gravity

Multiple Choice

This is ability to move a rocket in the right direction

• Drag

• Thrust

• Control

• Weight

• Center of Gravity

Multiple Choice

This is The average location of the weight of an object (that is, the balance point).

• Drag

• Thrust

• Control

• Weight

• Center of Gravity