jet propulsion; using car & balloon -how it works, why?

[baneys]

We are doing a 2nd grade science project on jet propulsion for science fair, using a toy car affixed with a balloon which will propel it fwd when inflated and released (and display bd on same). Try as we may, we have not managed to find any info on why this works (except for fact that the air pushing backwards propels the car forwards, which isn't enough for the display board!). Does anyone have any info (kid-friendly language and level) on how and why this works, and/or reference to any web sites that might have graphics or words we can use or adapt for the display bd? For example, maybe we can use a little call-out box on how a squid propels itself fwd by squirting the liquid out the back (we saw that on one site). Same on rocket and whatever comes out the back of it? But mainly an explanation of propulsion itself? Thanks so much! We need to finish it by Sunday night, but just found this site after researching unsuccesfully so far!

[ghariman]

Hi there,

Here is a website with many information on jet porpulsion:
http://en.wikipedia.org/wiki/Jet_propulsion

You should be able to get a lot of information from there.

Good luck.

[mine-ur]

I did this proejct a while back but it was more complicated then this.. but here are the sites I came across and thought theyr were good...

http://www.stevespanglerscience.com/experiment/00000246

<http://exploration.grc.nasa.gov/educati ... ktfor.html>.
And here was more info if it helps.....
Research

For the balloon car project the following ideas were taken into consideration:
· Forces: are vector quantities having both a magnitude and a direction. When describing the action of forces, one must account for both the magnitude and the direction. In flight, a rocket is subjected to four forces; weight, thrust, and the aerodynamic forces, lift and drag.
· Thrust: is the force, which moves the car through the air, and through space. Thrust is generated by the propulsion system of the rocket through the application of Newton's third law of motion
· Aerodynamic forces: are generated and act on the car as it flies through the air.

Benson, Tom. ‘Four Forces on a Rocket’. http://www.nasa.gov/. November 15, 2006. <http://exploration.grc.nasa.gov/educati ... ktfor.html>.

· Weight: force caused by gravity: the vertical force experienced by a mass because of gravity. Symbol W
· Force: influence that moves something: a physical influence that tends to change the position of an object with mass, equal to the rate of change in momentum of the object. Symbol F
· Drag: resistance to motion: the resistance experienced by a body moving through a fluid medium, especially by an aircraft when travelling through the air. Symbol D
· Lift: upward force acting on an aircraft: the combination of forces that act to cause an aircraft to leave the ground and stay in the air
· Torque: rotating force: force that causes rotation, twisting, or turning, for example the force generated by an internal-combustion engine to turn a vehicle’s drive shaft
· Aerodynamics: study of objects moving through air: the study of moving gases, especially the study of the forces experienced by objects moving through air
· Friction: resistance encountered by moving object: the resistance encountered by an object moving relative to another object with which it is in contact

Encarta ® World English Dictionary © & (P) 1998-2004 Microsoft Corporation
· Newton’s Third law: ‘for every action, there is an equal and opposite reaction’. This law works when two objects are interacting with each other, where they create something called ‘forces’. The first force is an action, and the second force is the reaction to the action. There are many natural forces at work when objects interact, such as friction, tension, gravity, and magnetic forces.

Henderson, Tom. ‘Physics Class, Lesson 4: Newton’s Third Law’. http://www.glenbrook.k12.il.us/. 1996-2004. December 1, 2006.
< http://www.glenbrook.k12.il.us/GBSSCI/P ... u2l4a.html >

How these Concepts Applies to the Balloon Car

· In the case of the balloon car, the force is the air coming out of the balloon. The reaction is the movement of the car- the air in the balloon pushes the car along. Also, the wheels of the car help the car move by reducing friction the car would have with the ground, and provide stability by keeping the body of the car balanced.
· Reducing the area of the car that is hitting the air directly reduces the drag.
· Reducing the friction of the axils will give a the car a more smooth ride which should translate into faster speed

hope this helps

[davidcastagna]

Please be kind this is my first ever post ;)
----
Baneys:

I had some additional ideas you might want to consider. Knowing some more about how this process works may help you find more information.

What makes the balloon want to move forward when you let go? It is due to lots of interacting effects. But two of them are most important: (1) Energy and (2) Conservation of Momentum. The Energy provides the fuel to make the whole thing go and the Conservation of Momentum is where the actual motion comes from.

The Energy part is because you blow air into the balloon. The air strains against the rubber and against the atmosphere around the ballon. That system of: the balloon + the air + the atmosphere doesn't want to stay that way. You can think of this as a little battery made of air. The energy stored in the balloon doesn't want to stay that way and the pressure on the air inside the balloon forces the air back out again when you let go. This simple concept will provide all of the energy for making the balloon move. You "fuled" the system (or "charged the air battery") by inflating the balloon with your breath. Now how do we make it move?

That's where Conservation of Momentum comes in. First though, what is Momentum?

Momentum can be measured. It is the mass of an object times the speed that the object is traveling. And the direction that an object moves matters. So for example, a basketball sitting on the grass has no momentum, but if you throw it, it now has a momentum because it's moving. And because direction matters, if you throw it in the opposite direction it has the opposite momentum. (If you could throw two balls in opposite directions at the same time, then the total momentum of both balls would cancel out.)

Okay now for Conservation of Mometum. This says that the momentum of any group of things must always stay the same... it must be conserved.

Now the whole balloon and air together had no momentum before you let go of the balloon because they weren't moving. And Conservation of Mometum says that the balloon and air together must always keep that same amount of momentum - none.

Well the air moves when you let go of the ballon right (the air rushes out of it)? Well that means the air actually has momentum. But how can we have momentum if the Conservation of Mometum says that since we had no momentum when we started, we must still have no momentum now? The only way that can happen is if something else moves in the opposite direction and cancells out the air's momentum. Well guess what moves? It's the balloon. The total amount of momentum stays zero (just like it was in the beginning) and momentum is Conserved.

Here's a little experiment you can do.... if you have a pair of ice skates and a basketball (observe all necessary safety precautions of course). Stand perfectly still on the ice with your skates holding the basketball. You aren't moving and neither is the ball. Now throw the ball as hard as you can away from you. You have now given the ball energy to make it move (just like the way the balloon pushes on the air inside it). You will find yourself sliding backwards on your skates slowly. Your momentum changes in response to the ball's momentum.

Now think of the balloon as you standing on your skates and the molecules of air as little basketballs. If you had an endless supply of basketballs and were throwing them over and over again in the same direction eventually you would be moving very quickly in the opposite direction. And this is what happens when the trillions of air molecules rush out of the balloon.

This is known in rocketry as Propulsion and the air/balls are known as Reaction Mass. The specific ways that make the air move and the balls move and a rocket's exhaust move are all a little different. But for propulsion that really doesn't matter. The basic principles are still the same.

So some other terms you might consider using in your searches:

• Conservation of Momentum
• Reaction Mass
• Propulsion
• Energy - this might be a little to broad of a subject. There's ALOT to Energy.

Also, here are a couple of links. Some of these are a little advanced but you might get some ideas there. The last one is pretty good actually:

• http://www.grc.nasa.gov/WWW/K-12/airplane/bgp.html
• http://www.braeunig.us/space/propuls.htm
• http://www.open2.net/battleofthegeeks/r ... ience.html