Twisty lever?

[Finless]

Does the lever principal apply to twisty things like undoing bottle caps?

To put it another way, can I exert a greater force when trying to unscrew a lid if my hands are further apart or does it make not make any difference? Did I just have a surge of energy when trying to get the lid off my flask (having failed using the Chinese Burn grip)?

[David]

when you got up this morning...nope cant say that....

how do you think of these things to ask

[jb2cool]

Yes but not in the say you explain, this is why torque wrenches have long handles.

The holding hand and the unscrewing hand can be as near or as far apart as you like and you won't acheive an advantage either way.

[tom]

Only if you increase the distance between the axis of rotation and the point at which you are applying force.
By using a wrench for example.

[jb2cool]

Only if you increase the distance between the axis of rotation and the point at which you are applying force.
By using a wrench for example.

That was what i was trying to find the words to say and failing.

[nigel hewitt]

Torque is measured in units like meter newtons or foot pounds.
If you use more distance then you get more torque, if you have more force you get more torque.

To misquote Archimedes: give me a torque wrench that is long enough and I shall turn the earth.

[Nickpicks]

The bottle screw cap is an inclined plane (curved around to make a helical thread).
The force you exert is used to push one plane against the other (and overcome friction between the two surfaces) This force is dependant on the coefficient of friction between the bottle and its cap, and the force between them (which is dependant on the amount of force used to originally tighten them (stored as tension in the cap/bottle neck). There's also the stickiness of the ketchup/jam that was around the threads which takes some force to unstick.

That force, multiplied by the radius of the thread, gives the amount of torque you need to unscrew the lid.
The torque your hand can give depends on the strength of your muscle (force) and the distance between your wrist and the bottle (lever length).
There's also the friction between your hand and the bottle / cap. (which depends on the material of the bottle/cap, the stickiness of your fingers, and the force you can squeeze them with).

The distance between the hand on the bottle and the hand on the cap makes no difference to the torque you can apply, but the further apart they are, the more difficult it is to keep it steady.

What you might need is to hold the larger end of the bottle (longer lever means less friction required between the fingers and bottle), and to use a strap wrench on the top (still a small lever, but rubber strap grips better, and the lever lets you exert force at a larger distance)


£2.50 here

[tom]

This force is dependant on the coefficient of friction between the bottle and its cap, and the force between them (which is dependant on the amount of force used to originally tighten them (stored as tension in the cap/bottle neck). There's also the stickiness of the ketchup/jam that was around the threads which takes some force to unstick.

Given that it's his flask, cooling of the contents may have led to an internal pressure reduction due to contraction of any gas inside the flask. Creation of a pressure differential between the inside of the flask and the atmosphere which would increase the amount of force needed to open it.

This assumes that (a) there was some airspace left in the flask rather than it being 100% full of liquid, and (b) the flask contents were originally hot, for instance tea or coffee as opposed to a (say) a weak lemon drink.

[Nickpicks]

Since it's a flask, in light of the recent thread about flasks, throw it away and buy a new one.

[Finless]

£2.50 here

I've got 3 of those doohickies in a box up in the roof at home!

[Finless]

Since it's a flask, in light of the recent thread about flasks, throw it away and buy a new one.

Throw it away ....... gasp ........ what about my 'green footprint'?

[tom]

what about my 'green footprint'?

Try an antifungal cream, or soaking your foot in bleach.

[CraigofScotland]

What if you use a twisty lever to twist the twisy thing?

[Finless]

What if you use a twisty lever to twist the twisy thing?

Then it becomes two .... sorry .... too twisty and even harder to undo.

Bloody flask! I swear I'm twisting space and time given the amount of effort taken to get the poxy lid off!

What it needs is a pressure relief widget that looks very similar to the rubber prong thingy inside the removable cover on the lid on my flask.

Oh FFS!

[PhilPage]

but rubber strap grips better

By spreading force almost equally arond the rim of the cap and flattening the force vector to its minimum (and therefore most efficient) angle