The Rope Drill

This is an old (but great drill) that can help take the "hit" out of a golf swing and make it a "swing."

Here's a drill you should try.

Get yourself a piece of rope about 42" long and 1"thick.
Take a normal grip, take it to the top of your swing and let the rope rest on the top of your shoulder. As you start down with your lower body "feel" like the rope stays on your shoulder as your hands head toward the ball. Let the momentum of the rope finish the swing. By allowing the rope to lag behind, you'll sense what it's like to draw the club like "the arrow out of the quiver".

You will also note that in order to accelerate the rope, you will have to pivot properly and pull it lengthwise, it's almost impossible to come over the top.

[From Gotham Golf Blog: The Rope and The Pivot]

If you are using your core properly the rope will wrap around your body smoothly at the end of your back swing, straighten out at the bottom of your swing and re-wrap around your body during your follow through.

If your swing is all arms the rope will be "whippy," it will be moving all over the place, and it will slap you hard on the back. This is how you know that you are not effectively swinging and using your core.

It's like a shock collar for your swing. If your swing is all arms you will find out quickly and want to fix it as soon as possible.

The easiest place to see this is in the very beginning of your swing. Never initiate your swing with your hands. If you are doing this the end of the rope won't move at first when you cock your wrists. This is bad.

[From Stop Leaking Power From Your Golf Swing Using This Weird Trick]