That funny I always thought that the Atmosphere was a Gas in it’s free state.

Yes, it is a gas…but when dealing with moving air (or things moving through it) it is referred to as a fluid…sorry, poor attempt at a joke…hence the smiley face. 😮

If it were true what you are saying about bearings then they would last forever, which is just laughable, i’ll say it again the more friction on a bearing [speed] the hotter it gets…

The point I was making (or trying to make) about friction is that when most people talk about ‘friction’ they are actually talking about two distinct, related but separate effects.

Friction that resists relative movement of objects in contact with each other; this is a force (a vector) and does not increase as the relative speed of the objects increase.

Heat that is generated as a result of relative movement of objects in contact with each other; this heat (a scalar) does increase as the relative speed of the objects increase.

When I said…

The fact that the conveyor will be spinning the wheels faster than during a normal take-off will not affect these forces…as they are forces of friction and these forces do not increase as the speed of the wheel increases.

…I was only referring to the friction force not increasing with speed.

Since this force, derived from the friction in the bearings, is the only force that could possibly prevent the aircraft from moving it is important to show that it will be less than the thrust produced by the propeller irrespective of how fast the belt goes.

Yes, the faster the belt goes the more heat will be generated in the wheel-bearings…

…but the force will remain constant and will be identical to the force, derived from the friction in the wheel-bearings, if the belt was stationary.

So if the plane can take-off from a stationary belt it can take-off from a moving belt…the only difference being the temperature of the wheel-bearings. 🙂

The motor driving the movement of the belt is providing the applying force against the imparted force of the aircraft that’s being applied to make the wheels turn.

:confused:

I think you are confusing force and motion…and the belt cannot apply a force to the aircraft, the airframe that is, but only to the wheels which are free to turn.

Here’s my take on the aircraft and the conveyor belt.

ok, with the aircraft sitting stationary on the belt thrust is applied by the engine, this would normally be imparted through the wheels in order to create ground speed.

You’ve lost me there…the propeller pushes on the air.

The wheels turn because the aircraft moves…the aircraft doesn’t move because the wheels turn.

Newtons Laws … equal and opposite forces means either stationary or at a constant speed…

Yes, Newton’s Laws apply but how does the belt apply a force to the aircraft?

The belt can only apply a force to the bottom of the aircraft wheels, and the wheels are free to turn so the forces are not equal-and-opposite…

…therefore according to another of Newton’s Laws the aircraft must accelerate. 🙂

I suppose a lot depends on the definitions of ‘robot’ and ‘intelligence’.

For example a machine that was able to move under its own power and make decisions with an on-board computer, decisions based on information about its surroundings from on-board sensors, to complete a planned task could be considered an intelligent robot.

What does that make an Exocet missile?

So much for Asimov’s Laws.

What ever happened to the Queens Flight Wessex helicopters after demob?

Wessex HCC4 serial XV733 is at the Helicopter Museum at Weston-Super-Mare (as is former Queen’s Flight Whirlwind HCC12 serial XR486) and (as Wessex Fan says) Wessex HCC4 serial XV732 is at Hendon.

So what makes the Space Shuttle heat up the faster it gets on hitting the Earths atmosphere…

I should have made it clearer that I was talking about the friction force between solid bodies in the case of the aircraft wheel-bearing, and that force doesn’t increase with increasing aircraft speed (unlike the ‘drag’ on the aircraft, but more of that later).

The friction that heats up the Space Shuttle is friction against the (thin) air, and air is a fluid (yes, it is :)) so that obeys different rules, aerodynamic rules (fluid friction).

Basically air-friction, drag, is proportional to the square of the aircraft (Space Shuttle) speed (but only within certain limits) so…

…if you double your speed, you get four times the friction force (drag)!

Of course this is what limits the speed of aircraft (and cars, trains etc.) moving through the air.

…and yes your Aircraft would take off, it gets it’s forward speed from the prop not the wheels, it just that the wheels would go round faster:D

At least somebody agrees with me! 😀

So its agreed then, neither of us knows what the ***** we are talking about, but find it impossible to stop, or is that just me!!

I wouldn’t go so far as that…I’m petty confident I’ve got it right and think I’ve demonstrated enough knowledge of statics/dynamics to support my argument…although I’ll admit my knowledge of ‘swan vestas’ let me down a bit! 😮

You seem pretty confident too and you’ve presented a reasoned argument and given me cause to re-examine my thinking on many occasions…and also to be more careful with my terminology.

We’d both like to think we’re right…but more importantly, we both like thinking…right? 🙂

If friction doesn’t increase with speed, why doesn’t a match light when slowly drawn across the abrasive?

Actually a match will light if you drawn across the abrasive very slowly…you just have to push down very hard…have a go. 🙂

Not sure of the relationship between friction and the lighting of a match…I’m not saying friction doesn’t light it…I just don’t fully understand it! :confused:

I should also point out that I’m talking about friction forces here…as I said originally:

The fact that the conveyor will be spinning the wheels faster than during a normal take-off will not affect these forces…as they are forces of friction and these forces do not increase as the speed of the wheel increases.

I should have made that clearer in my previous post…sorry. 😮

In a bearing, it is heat generated by friction that fuses the two surfaces together, the grease reduces friction (unless really cold); a wheel barrow has no wheel bearing, and at walking speed for short distances it doesn’t need one , tow one behind your car at 50mph (if you dare) and it will either seize or wear away to nothing, as a result of increased friction, as a result of speed.

‘Friction’ is strange…and I broadly agree with your statements about heat and wear.

The friction force does increase if you push the surfaces sliding against each other together…but not if you move the sliding forces faster relative to each other.

My observations are based on the Jodel A/C that I mentioned earlier, it couldn’t extricate itself from a relatively small pothole, even on full power…

But this is not friction. You can start to push a stationary car along a flat road…but if you place the same car against a kerb and try to push it onto the pavement you can’t…it is not friction that is stopping you.

I would have thought it possible to replicate the same opposing force, on the now mythical conveyor belt!!

I would say not…so long as the mythical conveyor was flat.

In truth I dont know the answer to this one, merely trying to fathom it out , without devoting a life time to the cause!!

Me neither…I’m not trying to pick a fight…promise! 🙂