In message , Mike Whittome
Hope This Helps
It took me about two years to work out what ROFL meant...
I see what you are driving at, but I maintain that my fingers and the
top link are in fact pulling down. If you hung a weight on the chain,
would you say that gravity was pushing on the weight?
All the best
Tony Jeffree, unusually misguided in this instance, writes
Actually, Tony, if you think about it , it goes like this.
Let us assume (a) that the rope is tied around the axle of your buddies
car in the good old fashioned way. Further (b) that the rope is tied to
a hook on the back of your towing vehicle.
The hook of your vehicle is pushing the eye of the rope. The rope eye
at the other end is pushing the axle. Thus your buddie's car is being
pushed down the road. QED
The rope itself is in tension.
Many laugh at me, some sneer, whilst the polite ones just smile! :)
Reminds me of an exhibit on flight that I saw once at a theme park in
the USA. The exhibit explained how a wing generates lift - the path
the air has to follow ovet the top of the wing is longer than the path
under the wing, so the airspeed is higher above the wing, causing its
pressure to be lower than the air pressure below the wing, hence lift
is generated by the difference in pressure. So far, so good.
The second part of the exhibit explained that a jet engine works by
air being taken in at the inlet of the engine at a low speed, and the
engine compresses the air and mixes mit with fuel, which ignites,
forcing the air out of the back at a higher speed, hence generating
But wait a minute...from the aerofoil description, slow air in at the
inlet, therefore high pressure, fast air out of the outlet, therefore
low pressure. Net pressure difference means that the resultant force
should be forwards, not backwards! So all of the world's jet aircraft
have their engines on back to front!
Nice test question Tony.
All I can say is "Non Linear System". Since a jet engine creates large
volumes of combustion products, the mass and volume of gas out is much
greater than the mass and volume of gas in.
So the engine really does create thrust (phew)
Now, back to my hacksaw........
Speaking from experience and misty memory you can't push birds.
Although I must admit some of the ones I've pulled in the past would do
serious damage to the reduction gears on a Scammell winch.
I fondly remember one in my early courtship days who went by the name of
I think this all stems from my Granddad, he told me "Never go out with
loose women" so since that day I have always set forth with a pocket full
of allen keys and a set of Bahco grips.............
Tony Jeffree writes further on this topic, and in so doing he helps me
to make my case .....................
In deed, Tony, very good. The higher pressure below the wing is
pushing up the aircraft.
You have to agree (well I hope you do) that thrust is push, within the
terms of the current and enjoyable discussion.
Mike Crossfield has answered this point far better than I ever could in
an adjacent posting.
ps, when we have finished here, perhaps we can start a whole new string
(possibly off topic, dependant on your point of view) on whether the
bung hole in a timber cask is animal, vegetable, mineral, or abstract.
Hmmm. Actually, I don't think Mike quite got the full answer there -
true the mass & volume out is greater than the mass & volume in, but
the key thing is surely that the larger mass & volume is being forced
out of the back of the engine, and accelerated, so there is an equal
and opposite force acting on the engine in the forward direction
(which is significantly bigger than any force that might result from
pressure differences in the two airflows).