Rocket flight principles

1. Objects at rest will stay at rest, and objects in motion will stay in motion in a straight line, unless acted upon by an unbalanced force.

2. Force is equal to mass times acceleration. F = ma

i.e. Higher the force, higher the acceleration. With the same force, heavier objects will have a lower acceleration.

3. For every action (force), there is always an opposite and equal reaction (force).

Center of Mass (CM or CG)

Center of Pressure (CP)

the exact spot where all of the mass of that object is perfectly balanced.

the rocket will rotate about this point.

The exact spot where surface area is the same on one side as the other. It exists when the air is moving past an object.

Which way does the weather vane arrow point? Which way is air moving?

The area towards the tail is higher so air imparts much more force on the tail end than the arrow end.

More Surface AreaHigher force than arrow end

The CP needs to be behind CM so that it moves only at the tail end.

You need to put CP behind CM in a similar manner to stabilize your rocket.

Thrust: the force that moves the rocket up in the air.

Drag: the force which resists the motion of an object as it moves through a fluid (e.g. air).

Lift: the force that is perpendicular to the direction of drag and depends on the density of the air

Weight: the force which pulls the an object down due to gravity.

Decrease Weight

Increase Thrust

Decrease Drag by improving aerodynamics

Refers to motion of fluids (liquid, gas, air) and their effects on the motion of a moving object.

Aerodynamic Forces: drag, lift

The shape of the object can be changed to improve aerodynamic forces.

Nose makes the air flow around the rocket

Mass at the top moves the center of mass closer to the nose

Fins increase surface area and move the center of pressure towards the bottom.

Water produces a sustained thrust but also moves the CM down.

1. Run the first simulator with different amounts of water.

Record Volume and Height Draw a Volume vs. Height

(line) graph What volume of water gives the

best height?

2. Run the second simulator with different number of fins, placement of fins, nose, and different rocket weights.

Explain what happens to the height when you change each of the above variables. How does mass of rocket, # of fins and their placement, and shape of nose affect the height?

If the mass of a rocket is 1.0 kg and a pressure of 100 psi is applied to it. Calculate its acceleration in m/s2 if there is no drag.Diameter of bottle = 1 inchpsi = pounds per square inch1 psi = 6 894.75729 Pascals1 pound of force = 4.448 Newtons1 Newton = 1 kg. m /s2

m

Fa

1. Measure total force using area and pressure in pounds

2. Convert pounds (of force) into “Newtons”

3. Take away the gravity force (m x g)4. Use force (F) in Newtons, mass (m)

in kilograms, and Newton’s second law to calculate the acceleration (a ) in m/s2.

Total Area = 1 inc x 3.14 = 3.14 square inch

Total Thrust Force = 100 psi x 3.14 sq.inch= 314 pound= 314 pound x 4.448 Newtons/

pound= 1397.38 Newtons

Gravity Force= 1 kg x 9.8 m/s2

= 9.8 Newtons Net Force

= 1397.38 – 9.8 = 1387.58 Newtons

Maximum acceleration

m

Fa

kg1

58.1387

258.1387s

m

The rocket’s speed would increase to 1387.58 m/s within a second!

Due to the drag force the acceleration is much much lower.

Drag increases as the rocket increases its speed!

y = maximum height of the rocket t = time for the rocket to fall to the

ground from its maximum height .

Measure t on a step watch. Start it when the rocket flips it direction.