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Do screwdrivers defy the laws of physics?

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Forum topic by Craftsman on the lake posted 11-13-2013 12:54 PM 1711 views 0 times favorited 46 replies Add to Favorites Watch
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Craftsman on the lake

2391 posts in 2104 days


11-13-2013 12:54 PM

Topic tags/keywords: question humor

A question was asked of my years ago and it always stuck with me.

Why is it that when you use a longer handle screwdriver you get more turning power?

Explanation of question. If you have a ratchet with a socket on it and you need more torque you get a longer handled ratchet or add an extension to the handle like a pipe. With a long enough handle the bolt or the ratchet will break. The longer handle acts as a longer lever. With a screwdriver a thicker handle will do the same thing but also, as long as you can get a good grip, a longer screwdriver will give you a similar effect. Got a stubborn screw? Get a longer driver. Even with two screwdrivers of the same handle size and bit size, one a foot long and the other a short tight space one. The longer one will turn a tough screw easier.

To me, it doesn’t seem to follow the mechanical advantage rules that we know of simple machines. There must be some explanation. I don’t think the laws of physics apply to all things but screwdrivers. Then again, I ask myself, “Are there more important things to think about than this?”.

-- The smell of wood, coffee in the cup, the wife let's me do my thing, the lake is peaceful.


46 replies so far

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Handtooler

1087 posts in 799 days


#1 posted 11-13-2013 01:23 PM

And, some of the larger screwdrivers have wrench flats just below the handle so one might get back into the physics realm by extending the leverage horizonially out the side, Huh?

-- Russell Pitner Hixson, TN 37343 bassboy40@msn.com

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deezldub

13 posts in 527 days


#2 posted 11-13-2013 01:24 PM

The way it was explained to me (servicing Japanese photo processing equipment for 20+ years) the longer shaft screwdrivers allow you to keep more pressure on the tip by leaning into the screwdriver, and it builds up rotational torque to help break the screw loose. It would usually just “pop” loose with the longer drivers and once you got it started you were good to go, We were issued both 8” and 12” philips (JIS standard which are a tighter fit) # 2 drivers that worked wonders for getting chemically crusted screws to break free without camout.

-- Steve

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bigblockyeti

1619 posts in 387 days


#3 posted 11-13-2013 01:24 PM

You can wrap your hand more completely around a small handle with a long shank given the distance you have between your hand and the work piece vs. having the same sized handle and a shorter shank. The psychological difference is there as well; you’re less likely to bear down on a smaller handled screw driver (most also have a shorter shank) due to the likelihood you’ll slip and hit your hand on the work piece. Metal can sharp, wood can be too and our sense of self-preservation tends to kick in and prevent us from hurting ourselves, especially when our experience tells us there’s probably a better option.

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404 - Not Found

2544 posts in 1636 days


#4 posted 11-13-2013 01:30 PM

If this was on “Call My Bluff” (a terrible British game show where three explanations are offered by eminent intellectuals to some obscure puzzle), I would go with answer 2, rotational torque advantage.

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jonah

453 posts in 1965 days


#5 posted 11-13-2013 01:46 PM

The answer is that you don’t get more turning power from a longer screwdriver. You get a bigger handle that you can apply more downward force and torque to.

If you had a stumpy screwdriver with a huge handle, you’d see the same effect.

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Tim

1273 posts in 628 days


#6 posted 11-13-2013 01:50 PM

There was a post on the Lost arts press blog about this. From an 1880 magazine article or something, and a few engineers chimed in.

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Tennessee

1447 posts in 1181 days


#7 posted 11-13-2013 01:52 PM

This is like a “mindworm”, something in your head you can’t quite figure out. I’ve imagined the scenario, and you are right about length, but shorter screwdrivers usually have somewhat shorter handles, and your body and arm is more cocked, eliminating some torque. I’m not really buying that rotational torque thing, where the shaft might actually act like a spring, wind ever so slightly and then add torque.
Long handle, long arm torque = more advantage.

-- Paul, Tennessee, http://www.tsunamiguitars.com

View HorizontalMike's profile

HorizontalMike

6942 posts in 1581 days


#8 posted 11-13-2013 02:08 PM

I would suggest that the longer shaft has more flex than the shorter shaft. When turning the longer shaft, some of the energy you are exerting on the screwdriver by twisting, is stored as ”potential energy”. When the screw/bolt finally “snaps” loose, this ”potential energy” is converted back to ”kinetic energy” thus giving a longer (time) push/twist in loosening the screw/bolt. This can be interpreted by some as being more powerful, though the same amount of total energy is exerted in both short and long handled screwdrivers.

That’s my 2-cents anyway…

-- HorizontalMike -- "Woodpeckers understand..."

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joeyinsouthaustin

1257 posts in 739 days


#9 posted 11-13-2013 02:11 PM

I think the answer is based more in ergonomics than in physics…. Send you question into the Mythbusters!!

-- Who is John Galt?

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a1Jim

112170 posts in 2244 days


#10 posted 11-13-2013 02:20 PM

It all seems “screwy” to me :)

-- http://artisticwoodstudio.com Custom furniture

View Gene Howe's profile

Gene Howe

5702 posts in 2095 days


#11 posted 11-13-2013 02:40 PM

While I have benefitted from the same phenomenon, I have no answer as to why it works.
OTOH, I can answer your final question: Probably, but where’s the fun in that?

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View ZacD's profile

ZacD

34 posts in 426 days


#12 posted 11-14-2013 04:42 PM

It has always been my impression that longer screw drivers also have larger shanks, and sometimes larger handles (this is apparent in your photo). So they would inherently carry more torque than shorter screw drivers, which typically have much thinner shanks. On another note, a larger shank is less likely to deform and twist against you and the handle holding it will also be less likely to deform and twist, because the shank has more surface area for the handle to hold.

The only other way it works is if it is in your head. Nothing has yet been discovered to defy any current laws of physics.

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jumbojack

1190 posts in 1291 days


#13 posted 11-14-2013 04:52 PM

It is another one of Gods gifts to man. Siphon is another that comes to mind.

-- Made in America, with American made tools....Shopsmith

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Danpaddles

539 posts in 978 days


#14 posted 11-14-2013 05:04 PM

I’ve broke a few laws in my life, but whenever I’ve tried to break the laws of physics, it never ended well.

If the longer shafted screwdriver works better, it is because the rotational force is closer to your body, where you can really put the torque to it.

No laws of physics have been broke. Now y’all move along, nothing more to see here.

-- Dan V. in Indy

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CharlieM1958

15702 posts in 2885 days


#15 posted 11-14-2013 05:14 PM

I have often wondered the same thing.

I don’t have the answer, but I do not believe it has anything to do with the bigger shaft/bigger handle/better grip theory some have suggested. I make this statement based on personal experience, and the five years I spent selling Craftsman tools part-time when I was in high school and college.

Take two Craftsman slotted screwdrivers. model #’s 41581 and 41582. They are identical in shaft size, tip size, and handle size, but one has a 4” shaft and the other a 9” shaft. The one with the 9” shaft will definitely turn a tight screw easier than the shorter one, even though all other factors are equal.

I believe HMike is sort of onto the right answer. I think the longer shaft flexes rotationally as you apply pressure, building up leverage. In other words, the force of the metal shaft trying to return itself to its normal shape is added to the rotational force applied by your hand.

-- Charlie M. "Woodworking - patience = firewood"

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