Transcript 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 Area
Higher 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.
Mass at the
top moves
the center of
mass closer
to the nose
Nose makes
the air flow
around the
rocket
Water
produces a
sustained
thrust but also
moves the
CM down.
Fins increase
surface area
and move the
center of
pressure
towards the
bottom.
Run the first simulator with
different amounts of water.
1.



Record Volume and Height
Draw a Volume vs. Height (line)
graph
What volume of water gives the best
height?
Run the second simulator with
different number of fins,
placement of fins, nose, and
different rocket weights.
2.

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 inch
F
a
 psi = pounds per square inch
m
 1 psi = 6 894.75729 Pascals
 1 pound of force = 4.448 Newtons
 1 Newton = 1 kg. m /s2

1.
2.
3.
4.
Measure total force using area and
pressure in pounds
Convert pounds (of force) into
“Newtons”
Take away the gravity force (m x g)
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
F
a
m
1387.58

1kg
m
 1387.58 2
s

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!

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
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.