Newton’s 3rd Law

[Fowlers FuryParticipant @fowlersfury]

Lockdown Distractions?

I yeald to none in my ignorance of basic physics but this short video, sent by a model engineering friend, even to me clearly contradicted Newton's 3rd Law:-
*Link*

I was only sent the vid not the YouTube link so it took a little tracking down. The posted comments explain …but perhaps amusing nevertheless?
(I tried following site guidance for embedding YouTube vids here. I couldn't get to " Scroll to the size boxes, go to "Customised" and type "450" into the width box " on my browser).

Another time-waster spotted on YouTube below. Perhaps I feel less concerned about my wasted workshop time now:-
Useless Machine

[Fowlers FuryParticipant @fowlersfury]

Transport Innovation (it says)

[Neil WyattModerator @neilwyatt]

While I am sceptical that he may be benefiting from a slope or other hidden assistance, no it doesn't violate the third law.

The intake of air a 'suck' will always be non-directional while the blow is, in this case the brolly is reversing the flow and entraining more air in the process which may increase the efficiency.

Neil

[Mick B1Participant @mickb1]

So those carts constructed by Dennis The Menace and the Bash Street Kids out of a pram-wheeled buggy and a hand-cranked windmill blowing into a sail would've worked after all?

I've missed out on a whole potential field of engineering…

Edited By Mick B1 on 30/10/2020 18:44:16

[JAParticipant @ja]

I don't think he could patent it. The big boys have got there first. It is very similar to the reverse thrust on a jet engine.

JA

[WatfordParticipant @watford]

Who is going to be the first here to try it out?

Mike

[Pete RimmerParticipant @peterimmer30576]

Posted by Neil Wyatt on 30/10/2020 17:57:13:

While I am sceptical that he may be benefiting from a slope or other hidden assistance, no it doesn't violate the third law.

The intake of air a 'suck' will always be non-directional while the blow is, in this case the brolly is reversing the flow and entraining more air in the process which may increase the efficiency.

Neil

I think that the air blower is turning the brolly into a circular wing. Air can only be spilled over the trailing edge of the brolly which is dragging otherwise still air from in front over the curved surface, The speed increase over the outside surface is causing a low pressure zone i'e' 'lift' which provides the forward motion.

[Grindstone CowboyParticipant @grindstonecowboy]

Electric skateboard – in the initial pictures there's just four castors on the bucket, in the later shots there's definitely something more underneath.

Rob

[Michael BriggsParticipant @michaelbriggs82422]

The engine of the blower increases the kinetic energy of the intake air so the air output has more energy than the air input.

The umbrella is a distraction, the force of the air output from the blower pushes against it providing thrust. He would be better off ditching the umbrella and just pointing the blower to the rear leaving a spare hand to watch rubbish on the internet.

[Pete RimmerParticipant @peterimmer30576]

Posted by Grindstone Cowboy on 30/10/2020 19:19:55:

Electric skateboard – in the initial pictures there's just four castors on the bucket, in the later shots there's definitely something more underneath.

Rob

Yes you're right, it's got a powered skateboard underneath.

Cute 😀

[JAParticipant @ja]

It would be interesting to see if he could move, without the electric skate board and umbrella, by using the blower alone.

It reminds me of Jeremy Clarkson’s attempt at using a CO2 fire extinguisher to propel himself on a similar buggy.

JA

Edited By JA on 30/10/2020 20:09:04

[Fowlers FuryParticipant @fowlersfury]

I should have made it clearer in the first post.
Instead of " The posted comments explain " I should have written, "Commenters on the YouTube page identified the electric skateboard".
I noticed his janitor's bucket when in motion had acquired suspension but only after reading the posted comments did I watch again and see the skateboard.

[Michael GilliganParticipant @michaelgilligan61133]

Presumably our Janitorial hero watched Barbarella

**LINK**

MichaelG.

[ZanParticipant @zan]

Perhaps I’m not understanding this. A jet engine produces thrust to an aircraft by pointing backwards, pushing the plane in the opposite direction this idea seems to say if you tie a parachute to the output of the engine, then the plane will fly backwards

Forces work in Equal and opposite directions
But it is a good bit of fun

[Sam StonesParticipant @samstones42903]

Without the skateboard, steering on castors would be near impossible.

I’m with Pete and assert clearly it's reverse thrust.

Sam

[not done it yetParticipant @notdoneityet]

Isn’t it Newton’s Second Law. Different forces in the two directions providing a resultant acceleration (until the opposing forces are equal) – when Newton’s First Law will apply?

However, the acceleration and terminal speed would not be anywhere near as great had he not cheated with the powered skateboard.🙂

[John HaineParticipant @johnhaine32865]

So DC9s have rear jet engines and apply reverse thrust with pivoted scoops that hinge into the jet stream. I've seen them at O'Hare back off the stand using reverse thrust. How does that work?

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.youtube.com/watch%3Fv%3DzG_u_B5d7cQ&ved=2ahUKEwjt6evpsN7sAhUuUhUIHeAUC5wQwqsBMAF6BAgJEAw&usg=AOvVaw0ymi5AwjYMaR4qBq2XGKew

Edited By John Haine on 31/10/2020 08:15:07

[Mick B1Participant @mickb1]

Posted by John Haine on 31/10/2020 08:10:22:

So DC9s have rear jet engines and apply reverse thrust with pivoted scoops that hinge into the jet stream. I've seen them at O'Hare back off the stand using reverse thrust. How does that work?

**LINK**

Edited By John Haine on 31/10/2020 08:15:07

Not very efficiently and maybe straight-line only. The clamshells divert the exhaust stream forward. They do it on landing too – hard, especially on short runways. Lot of force on those pivots.

[Ady1Participant @ady1]

Works better when the earth is flat

[MeunierParticipant @meunier]

Posted by John Haine on 31/10/2020 08:10:22:

So DC9s have rear jet engines and apply reverse thrust with pivoted scoops that hinge into the jet stream. I've seen them at O'Hare back off the stand using reverse thrust. How does that work?

**LINK**

Edited By John Haine on 31/10/2020 08:15:0

Such manoeuvering procedures mostly banned these days for both rear and wing mounted engines, experience found that engines were being damaged by FOD thrown up by reverser efflux was being ingested into the engine air intakes – cheaper to call for a tug.
DaveD

[Mick B1Participant @mickb1]

Posted by Meunier on 31/10/2020 15:22:13:

Posted by John Haine on 31/10/2020 08:10:22:

So DC9s have rear jet engines and apply reverse thrust with pivoted scoops that hinge into the jet stream. I've seen them at O'Hare back off the stand using reverse thrust. How does that work?

**LINK**

Edited By John Haine on 31/10/2020 08:15:0

Such manoeuvering procedures mostly banned these days for both rear and wing mounted engines, experience found that engines were being damaged by FOD thrown up by reverser efflux was being ingested into the engine air intakes – cheaper to call for a tug.
DaveD

Why wouldn't that happen on runway braking? Is it kept cleaner of random debris?

[Martin KyteParticipant @martinkyte99762]

In the UK the blower would be pointing backwards and the brolly used to keep the rain off.

regards Martin

[MeunierParticipant @meunier]

Posted by Mick B1 on 31/10/2020 15:48:09:

Posted by Meunier on 31/10/2020 15:22:13:

Posted by John Haine on 31/10/2020 08:10:22:

So DC9s have rear jet engines and apply reverse thrust with pivoted scoops that hinge into the jet stream. I've seen them at O'Hare back off the stand using reverse thrust. How does that work?

**LINK**

Edited By John Haine on 31/10/2020 08:15:0

Such manoeuvering procedures mostly banned these days for both rear and wing mounted engines, experience found that engines were being damaged by FOD thrown up by reverser efflux was being ingested into the engine air intakes – cheaper to call for a tug.
DaveD

Why wouldn't that happen on runway braking? Is it kept cleaner of random debris?

Don't know for sure but think that the aircraft is still travelling forward at a sufficient speed to 'overtake' any FOD thrown up by the reverse thrust, which usually reduces as the aircraft reduces speed.
Is it kept cleaner of random debris ? usually-yes- and subject to regular inspections whereas the parking bays can be grubby/dusty places where people work, not to mention loose baggage containers which could be blown around with reverse thrust
DaveD

[mark costello 1Participant @markcostello1]

they probably have never lifted the Wife's luggage, could have been used to anchor Noah's Ark.

[Henry ArtistParticipant @henryartist43508]

Posted by Neil Wyatt on 30/10/2020 17:57:13:

While I am sceptical that he may be benefiting from a slope or other hidden assistance, no it doesn't violate the third law.

The intake of air a 'suck' will always be non-directional while the blow is, in this case the brolly is reversing the flow and entraining more air in the process which may increase the efficiency.

Neil

I believe Neil's analysis is correct. Exactly the same principle is used when a boat fitted with a kitchen rudder is moving astern.

The kitchen rudder seems to be something of a rarity these days though they can be super useful to the model steam boat fraternity. The engine and propeller only run in one direction thus simplifying construction. To a certain extent speed can also be controlled by the rudder. When steering the boat a kitchen rudder behaves rather like a steerable Kort nozzle.

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