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Newton's 3rd Law

Transport Innovation (it says)

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Fowlers Fury30/10/2020 15:01:01
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355 forum posts
80 photos

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


Neil Wyatt30/10/2020 17:57:13
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18316 forum posts
718 photos
77 articles
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 B130/10/2020 18:42:45
1767 forum posts
91 photos

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...

wink

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

JA30/10/2020 18:46:19
1003 forum posts
54 photos

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

Watford30/10/2020 18:51:30
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135 forum posts
11 photos

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

face 1

Mike

Pete Rimmer30/10/2020 19:08:23
807 forum posts
50 photos
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 Cowboy30/10/2020 19:19:55
357 forum posts
28 photos

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 Briggs30/10/2020 19:57:47
198 forum posts
9 photos

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. wink 2

Pete Rimmer30/10/2020 19:58:20
807 forum posts
50 photos
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 :D

JA30/10/2020 20:08:12
1003 forum posts
54 photos

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 Fury30/10/2020 20:43:56
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355 forum posts
80 photos

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 Gilligan30/10/2020 22:38:21
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16616 forum posts
723 photos

Presumably our Janitorial hero watched Barbarella

**LINK**

https://youtu.be/dD0bBj_e5B4

MichaelG.

Zan30/10/2020 22:59:24
197 forum posts
16 photos

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 Stones31/10/2020 00:25:49
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780 forum posts
308 photos

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 yet31/10/2020 07:23:01
5124 forum posts
20 photos

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 Haine31/10/2020 08:10:22
3422 forum posts
184 photos

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 B131/10/2020 09:38:47
1767 forum posts
91 photos
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.

Ady131/10/2020 09:42:30
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3938 forum posts
522 photos

Works better when the earth is flat

Meunier31/10/2020 15:22:13
370 forum posts
5 photos
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 B131/10/2020 15:48:09
1767 forum posts
91 photos
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?

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