What is the "Sweet Spot"?
The "sweet spot" is that area of the bat where you get the most 'pop' out of the bat. It is the ideal place at which to hit the ball for distance. On most bats the sweet spot is found about 17 cm from the end of its barrel. Every hitter can feel when you have hit the sweet spot or not, if you swing, and connect and you dont really feel a thing then its a good bet that you hit at the center of the sweet spot. If your hands sting after you hit the ball, then you missed the sweet spot, and there are times when you really wished you hit that "spot."
The sweet spot exists due to vibrations occuring in the bat. You become quite aware of these vibrations if you hit the ball off the end of the bat or too close to the handle. Actually the sweet spot exists from the lack of vibartions that occur at that spot. When a bat is swung it is bent enough to excite two different frequencies of vibration. These vibrations create two seperate nodes towards the end of the bat. A node is a point where the a vibrations amplitude equals zero, basically there's no vibrations at this point. The area between the two nodes in a bat is the sweet spot.
www.gmi.edu/~drussell/Demos/bats/bat1-bend.html
If you hit the ball at a place too far away from the node than alot of energy is transfered from the ball and through the bat exciting the vibrations even further. As you see on the diagram above the vibrations get worse as you move towards the handle of the bat. When the bat is struck between the nodes than little energy is transfered into the bat's vibrations. Which allows the ball to move from the bat with a greater speed, its not enough to hit a home run every time but it does feel much better.
How to Find the Sweet Spot
To find the sweet spot in a bat, all you need is a hammer, bat, and a friend may be helpful for an extra set of hands. Have your friend hold the bat lightly from the knob of the handle on the bat. Start tapping with the hammer from the barrel of the bat. Your friend, or however is holding the bat, will be able to feel the vibrations as you strike the bat, when you hit the bat and no, or little, vibrations are felt then its a good bet you have found the 'sweet spot'. You can also tell by the sound that the bat will make when its struck at its node.
www.exploratorium.edu/baseball/sweetspot.html