Model Rocketry. The Science Behind the Fun

Transcription

1 Model Rocketry The Science Behind the Fun

2 Topics History of Rockets Sir Isaac Newton Laws of Motion Rocket Principles Flight of a Model Rocket Rocket Propulsion Forces at Work

3 History Rockets and rocket powered devices have been in use for more than 2,000 years! Chinese used rockets for celebrations. Were used in combat in 1232 A.D. to fight off a Mongol assault on Kai-fengfu.

4 History For centuries, only small rockets were used in battle. 20 th Century saw the greatest developments in rocketry. Space Programs rely heavily on rockets today.

5 Sir Isaac Newton Science of rocketry began with Newton. Wrote a book that is called Principia. Laid out three important principles that govern all motion. Called the Three Laws of Motion.

6 Three Laws of Motion First Law 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. Second Law Force is equal to mass times acceleration. Third Law For every action there is always an opposite and equal reaction.

7 First Law Referred to as the Inertia Law. Basically put, the motion of an object stays the same unless something happens to it to change the motion. We call this property of objects inertia.

8 Motion? What is motion? Motion occurs when the position of an object changes in relation to a reference object. A reference object is always defined to be motionless!

9 Unbalanced Forces When unbalanced forces act on an object, motion occurs. Think of a scale! If one side becomes heavier than the other, then it drops down (Motion!).

10 Second Law Called the Force Law. The force of an object is equal to its mass multiplied by its acceleration. Compare the forces of a bicycle and a train with the same acceleration!

11 Third Law The Equal But Opposite Law. This is the main law governing flight. In order to fly, objects must react in the opposite direction of a force.

12 Kite Flight

13 Kite Flight Wind

14 Kite Flight Wind Deflected Wind

15 Kite Flight Kite Movement Wind Deflected Wind

16 Kite Flight Kite moves in the opposite direction from the deflected wind with a force equal to the wind! Kite Movement Wind Deflected Wind

17 Rocket Principles A rocket can only lift off because it releases gas out of its engine. The rocket pushes on the gases. The gases push on the rocket.

18 Rocket Principles In rockets, the action is the release of gas from the exhaust. The reaction is the movement of the rocket in the opposite direction. The thrust must be greater than the mass to lift off.

19 Second Law Rockets for space flight tend to have a lot of mass. To achieve lift off, they must accelerate rapidly! So gases must escape at a great rate of speed.

20 Second Law In order to reach Low Earth Orbit, rockets must reach speeds above 28,000 km/hr. To leave Earth, the speed must reach 40,250 km/hr. Escape Velocity

21 Putting It All Together An unbalanced force must be exerted for a rocket to lift off from a launch pad. The amount of thrust needed is determined by mass of the rocket and the speed the escaping gas. The reaction of the rocket (Motion) is equal to the opposite direction of the action (Thrust).

22 Flight of a Model Rocket

23 Good Way to Learn Safe and inexpensive. Learn about: Aerodynamics Forces Affecting Flying Vehicles Laws of Motion Already looked at in this show. Principles of Flight More than just rockets.

24 Flight Stages Launch The thrust of the engine is greater than the weight of the rocket. Rocket weight generally does not change much during the flight. Allows it to leave the launch pad.

25 Thrust Force that moves an aircraft through the air. Propels rockets as well. Mechanical Force Produced by engines of plane or rocket Engine does work on the gas (Third Law). Gas pushes engine in return.

26 Model Solid Rocket Engine Two main types of rocket engines. Solid and liquid. Models use solid fuel. The gases generated by the burning fuel push out in all directions. Most force hits engine casing.

27 Model Solid Rocket Engine Some gas escapes from the nozzle. This creates an unbalanced force. According to the Third Law, there must be an equal but opposite reaction to rebalance the forces. Thus the engine moves in the opposite direction.

28 Flight Stages Powered Ascent Thrust is still greater than the weight of the rocket. Aerodynamic forces of lift and drag begin to act on the rocket. Model rockets depend on aerodynamics for stability. Not true of large rockets.

29 Lift On an airplane, most lift is generated by wings and tail surfaces. In rockets lift is generated by the body and the fins. Lift is generated when a solid object moves through a fluid substance.

30 No Fluid, No Lift Lift is created when a flow of gas is turned by a solid object like a wing. The flow is turned in one direction, the lift is generated in the opposite direction. Newton s Third Law again! Liquids and gases are fluids in nature because their molecules move. All model rockets spin due to aerodynamics!

31 Drag Drag opposes the motion of objects moving through a fluid. Every part of the object generates drag. Friction is created as the fluid makes contact with the craft.

32 Drag Drag created by this method is called skin friction. Another type of drag is called form drag. In this type, the shape of the craft determines how much friction is generated. There are other, less important forms of drag.

33 Flight Stages Coasting Flight Relies on the inertia to continue motion. Other forces begin to act to slow the rocket down Gravity Drag

34 Flight Stages Ejection Charge Separates the nose section from the body of the rocket. Allows chutes to open. In multistage rockets, allows exposure of next set of engines for more powered flight. Night launch of the Cassini Satellite.

35 Flight Stages Slow Descent Usually uses a parachute. Apollo capsules had three for return to Earth. Streamers and helicopter motion is also used on models. Shuttles glided down.

36 Flight Stages Recovery Usually pretty simple with model rockets. Walk and get the rocket. Sometimes lands in tree or on building! More complex with manned flights.

37 Main Things! Whenever using model rockets: Be Safe! Have Fun! Remember some of the Science we have discussed.

38 Other Launches Atlas Launch Model Launch