Posted by: Major Dan (markj89@charter.net) on Wed Dec 20 09:59:33 2000

Jack
>
> Is this not like the following examples?
>
> When you are using a nail gun or staple gun--if you don't hold it firmly (often need 2 hands) the staple or nail won't go completely into the wood because your hands need to counteract the rebound effect.
>
> In golf, putting and around the greens--you want the grip loose for some shots to keep the ball dead (keep it from being hit too hard.
>
> Maybe not a good example, but when a batter bunts--not only does he not swing the bat--he holds it extra loose.
>
> Can anyone think of other examples?
>
> Tim
>
(From 'The Physics Classroom' website)
http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l1a.html

Newton's Second Law of Physics:
Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.

Force Definition:
A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
A force is a vector quantity. A vector quantity is a quantity which has both magnitude and direction. To fully describe the force acting upon an object, you must describe both the magnitude (size) and the direction.

Newton's Third Law of Physics:
"For every action, there is an equal and opposite reaction."
The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.


In hitting, both the ball and bat hit each other with equal force. However the ball does not just drop to the ground and the bat stop. In fact this would happen if the mass of each were equal (head-on car crash) AND the forces were applied in the opposite directions.

Instead we have a head-on crash closer to a locomotive and a bicycle - the bike flies off and the train keeps going. However the ball-bat collision is quite so lopsided. Since momentum is mass * velocity, the ball that has less mass rebounds while the bat that has more mass slows somewhat. Try hitting a shotput with a whiffle ball bat for contrast - its all in the relative mass.
- an equal and opposite reaction

However, forces have two components -
When the ball strikes the barrel end of the bat, it applies a force to the bat that is applied as torque. The pivot point is the hands' grip on the bat handle. There is considerable leverage since the force is being applied at the far end of the bat. Since torque is 'rotational', the force applied does not push the bat back, but tries to turn it around the hands holding the bat - angular momentum. A one handed swing has minimal torque applied in the opposite direction. This force is more or less unopposed. A two-handed swing can apply torque opposite that applied by the ball.
So, I'm deducing that the two handed swing's torque counters the torque applied by the ball while a one-handed swing does not.

Secondly, both the ball and bat have a center of percussion or sweetspot. The bat acts as a spring. There are seven types of forces and hitting contact uses two - applied (the bat/ball collision) and spring forces.
The bat bends back from its normal position and wants to return to that normal position. However, the more the bat 'gives' with contact, the less it bends or spring-loads. The two-handed grip not only applies torque, it provides a firm base against which the bat can bend and spring back. Both wood and metal bats have spring to them. You can tell a dead bat from a live one.
Lastly, the bat (and ball) have a center of percussion. When the ball hits the sweetspot of the bat, its spring forces are fully employed. On the end, handle or label of the bat, this spring is noticably reduced.
At Tim noted, if you loosen the two-handed grip and bunt the ball, the spring is gone and the ball does not rebound.

So, you may be able to swing almost the same speed one or two handed, but you don't generate the same forces and probably won't hit the ball as far.

Hope this 'voodoo' science passes inspection