B Can You Propel Yourself Back on a Chair?

[Skeptic Tom]

TL;DR Summary

Is it possible to sit on a chair and self propel oneself back while still sitting on it?

It may seem a bit silly this but I was told by a friend that it is possible to sit on a chair, wooden or plastic and propel oneself back by using ones legs, say a distance of one meter, while still sitting on the chair, in one sudden quick movement. I tried it but found it impossible. The plastic chair did not move one centimetre, the legs just twisted and almost broke. Isn't that a bit like saying to someone, 'can you lift a basket up while standing inside it'? I asked the person to try it themselves but they said they were not fit enough to do it, adding that a fit agile young person could do it. Perhaps if the chair had wheels on it, then yes, one could propel oneself back, but not an ordinary garden or dining room chair. Thoughts?

 

[HallsofIvy]

I'm not sure what you mean by "propel oneself back by using ones legs". Certainly, you can push yourself back by pressing your feet against the floor!

If you mean that you sit in the chair and, without making contact with the floor or other "external" structure but just "waving" you legs and feet, the "maybe"! But in order to move at all there would have to be some kind of friction so that you legs and feet are, in fact, making contact with something. If there is no friction, or only neglible friction then, no, "conservation of momentum" prevents any "external" motion without "external" force.

 

[wrobel]

Summary:: Is it possible to sit on a chair and self propel oneself back while still sitting on it?

can you lift a basket up while standing inside it'

you are standing inside your shoes. Can you jump?

 

[anorlunda]

Mexican Jumping Bean

 

[Skeptic Tom]

Thanks for your reply HallsofIvy…... I mean while the person is sitting on the chair with their legs and feet tucked under the chair and with one sudden movement, using their feet against the surface (wooden floor, tile floor or stone floor) to push the chair back about one meter while still remaining seated.With just one initial force using the feet against one of these surfaces to propel oneself back. Only one big push is permitted. So, yes, there would be contact with the floor. I tried it on the three surfaces listed but no movement. I am sure it would be possible if one was sitting on a chair sitting on a very smooth surface, such as ice and using ones legs to push against, say a wall. That would work but I can't see how it would work on the surfaces listed. I was not able to push myself back as described.

 

[Dale]

Summary:: Is it possible to sit on a chair and self propel oneself back while still sitting on it?

Perhaps if the chair had wheels on it, then yes, one could propel oneself back

This is the key. There needs to be some friction, but not too much.

 

[A.T.]

I am sure it would be possible if one was sitting on a chair sitting on a very smooth surface, ...

So you see that there is nothing in physics that prevents this in principle?

... but I can't see how it would work on the surfaces listed. I was not able to push myself back as described.

Practice, practice, practice...

 

[hutchphd]

You need to get your weight over your feet when you push and then back onto (the less "frictiony") chair for the slide.
This is sort of the way cross country skis provide propulsion.

 

[phinds]

This is the key. There needs to be some friction, but not too much.

Exactly. @Skeptic Tom, there can be a situation where jerking your legs out suddenly will create enough force to overcome the friction of the chair/floor and then drawing them back in slowly will not create enough force to overcome that friction. You could go all the way across the room with multiple jerks.

 

[Vanadium 50]

If you watch The Blues Brothers, you can see Jake and Elwood do this when visiting The Penguin.

 

[Keith_McClary]

This is sort of the way cross country skis provide propulsion.

It's easy to do standing on a small carpet or piece of fabric.

 

[kuruman]

Summary:: Is it possible to sit on a chair and self propel oneself back while still sitting on it?

It may seem a bit silly this but I was told by a friend that it is possible to sit on a chair, wooden or plastic and propel oneself back by using ones legs, say a distance of one meter, while still sitting on the chair, in one sudden quick movement. I tried it but found it impossible. The plastic chair did not move one centimetre, the legs just twisted and almost broke. Isn't that a bit like saying to someone, 'can you lift a basket up while standing inside it'? I asked the person to try it themselves but they said they were not fit enough to do it, adding that a fit agile young person could do it. Perhaps if the chair had wheels on it, then yes, one could propel oneself back, but not an ordinary garden or dining room chair. Thoughts?

People do it all the time sitting on office chairs with casters. This contemporaneous thread deals with the question of why it is easier to roll than to slide. Your experiments illustrate what is said in that thread. A word of caution: it is voluminous and it's up to you to separate the wheat from the chaff.

 

[HallsofIvy]

It's a matter of the friction on the soles of ones feet and the friction on the feet (or casters) on the chair. And that, of course, also depends on the floor surface.

 

[phinds]

It's a matter of the friction on the soles of ones feet and the friction on the feet (or casters) on the chair. And that, of course, also depends on the floor surface.

No, you can't USE your feet on the floor. That was the point of the question although it wasn't stated very clearly.

OOPS ... I see that he clarified in post #5 that is IS talking about using your feet on the floor, so my post #9, while correct, did not address his question.