Why is it so easy for you to use a screw driver to loosen/tighten screws, but nearly impossible/very hard to do it with just your hand?

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Why is it so easy for you to use a screw driver to loosen/tighten screws, but nearly impossible/very hard to do it with just your hand?

In: Physics
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Your fingers cannot squeeze the screw tight enough to turn it without slipping. If you were wearing special non-slip gloves then maybe it would work, but then the thickness of the gloves would make it hard to squeeze the screw at all

To tighten a screw by hand, you’re limited to gripping just the head. This would require you to pinch it between two finger tips, which has a maximum grip strength of maybe 20 pounds. Friction between skin and metal is iffy, so we’ll say that you only get 10 pounds of grip. That is applied at a distance of, at best, a quarter inch from the center. This gives you a torque (rotating force) on the screw of 2.5 inch-pounds.

With a screwdriver, you could instead grip with 60 pounds at least since you can use your whole hand. On top of that, you’re twisting farther from the center – maybe 3/4 of an inch instead of 1/4. That allows for 22.5 inch-pounds, assuming the same friction from earlier. With a good rubber handle, friction may also be noticeably higher.

The handle of the screwdriver is what makes it easier. If the handle was the same diameter as the screw, it wouldn’t be any easier (except that it might be easier to grip it so you could apply more force). Since the diameter of the handle is larger than the screw, you can apply more torque and then turning the screw becomes easier.

Levers convert a small force applied over a long distance to a large force applied over a small distance. A long lever lets you lift a heavy weight with less apparent effort.

The rotational equivalent of linear force is torque. The handle on a screwdriver has a larger diameter than the screw head. The wider the handle, the less apparent effort has to be used.

It’s also easier to grip the screwdriver. You use different, stronger muscles to make a fist (around the handle) than you do to pinch (the screw) with your fingertips.

the screwdriver is providing you with leverage. it’s the same principle that Archimedes described — same reason big nail clippers easier to use then tiny ones; you’re using a big motion to concentrate your energy in a small area