Saw this on another thread. Momentum = mass x velocity, which is what you should be looking at. JAD, when using force, mass and velocity are not equally as important.
Force = Mass x Acceleration
Therefore, bat size and swing speed are equally important. If you DD can swing a 22oz bat at 60MPH, the force generated is 1320 (22 x 60). If she moves up to a 23oz bat she would need to have a swing speed of greater than 57.4MPH to generate increase force (1320/23), and if she moved down to a 21oz bat she would need a swing speed of 62.8MPH to generate the same force (1320/21).
Saw this on another thread. Momentum = mass x velocity, which is what you should be looking at. JAD, when using force, mass and velocity are not equally as important.
My DGD went to her first batting lesson this week. She just turned 11 and is using a 31/19.5 bat. She about 5'2" and 120lbs. New coach says bat is too light. My DGD says (to me) that she dosen't like the 31/19.5 because it's too heavy. She is having trouble deciding when to pull the trigger and is usually late, thus she likes the lighter bat. I know you guys have seen this before so, what advice do you guys have for me.
Thanks in advance
First it is very important IMO at this age that you instill in them that they swing at every pitch until they see its a bad pitch and stop the swing...the only decision is a no...as they get older and the pitching gets better it doesnt matter how light the bat is if you wait to see its a good pitch and then start the swing you are going to be late...
Sue Enquist - "Mental Game" (part 5 of 5) - YouTube
iMlearning (06-02-2012)
I wish that the -11s and -12s had never been produced. It is so difficult to talk some girls, but mostly the parent into a -10 bat. How on earth did we ever play softball without feather weight bats?
OK, I'm not an EXPERT in physics but, you're talking about essentially the same thing.
momentum is calculated as p = mv where p = momentum and m = mass and v = velocity.
force calculation is F = ma where m = mass and a = acceleration.
There is only a subtle difference, and you'd have to look up the difference. As here;
If an object is moving in any reference frame, then it has momentum in that frame. It is important to note that momentum is frame dependent. That is, the same object may have a certain momentum in one frame of reference, but a different amount in another frame. For example, a moving object has momentum in a reference frame fixed to a spot on the ground, while at the same time having 0 momentum in a reference frame attached to the object's center of mass.
The amount of momentum that an object has depends on two physical quantities: the mass and the velocity of the moving object in the frame of reference.
Example: a model airplane of 1 kg traveling due north at 1 m/s in straight and level flight has a momentum of 1 kg•m/s due north measured from the ground. To the dummy pilot in the cockpit it has a velocity and momentum of zero.
According to Newton's second law, the rate of change of the momentum of a particle is proportional to the resultant force acting on the particle and is in the direction of that force.
or just simply
F = ma
where F is understood to be the net force (or resultant).
Example: a model airplane of 1 kg accelerates from rest to a velocity of 1 m/s due north in 1 s. The thrust required to produce this acceleration is 1 newton. The change in momentum is 1 kg•m/s. To the dummy pilot in the cockpit there is no change of momentum. Its pressing backward in the seat is a reaction to the unbalanced thrust, shortly to be balanced by the drag.
Confused? see more here:
How is force related to momentum?
Answer:
Momentum measures the 'motion content' of an object, and is based on the product of an object's mass and velocity. Momentum doubles, for example, when velocity doubles. Similarly, if two objects are moving with the same velocity, one with twice the mass of the other also has twice the momentum.
Force, on the other hand, is the push or pull that is applied to an object to CHANGE its momentum. Newton's second law of motion defines force as the product of mass times ACCELERATION (vs. velocity). Since acceleration is the change in velocity divided by time, you can connect the two concepts with the following relationship:
force = mass x (velocity / time) = (mass x velocity) / time = momentum / time
Multiplying both sides of this equation by time:
force x time = momentum
To answer your original question, then, the difference between force and momentum is time. Knowing the amount of force and the length of time that force is applied to an object will tell you the resulting change in its momentum.
Still confused!? Here's another explanation;
Newton's 2nd Law tells us that force = mass x acceleration ( F = ma ). Since acceleration is just how velocity changes over time, we can write this as
F = m * v/t
Multiply both sides by time to arrive at
F t = m v
Since mv is momentum, we can see that the momentum conferred to an object by a force equals the force times the time the force is applied. Thus if a 15 Newton force to the right is applied to an initially stationary object for 3 seconds, it will have a momentum of 45 kg m/s to the right.
Most students who ask this question are usually trying to figure out the reverse situation, however. If an object hits me with a certain amount of momentum, how much force does it hit me with? Note that due to Newton's 3rd Law, this can be calculated the same way. If a thrown egg hits your hand with a momentum of 5 kg m/s, the force it applies to your hand depends on the time it takes for your hand to absorb the momentum. If you hold your hand very stiffly (and try to make the egg stop in a very short period of time) the ball exerts a high force on your hand, e.g. 100 N for 1/20th of a second.
Last edited by jbooth; 05-31-2012 at 04:32 PM.
Amy,
Any suggestions on trying to convince my DGD to give a -10 bat a good chance. I know she has the strength. I believe she need lots and lots of live hitting with the heavier bat. What do you think? I respect yu opinions.
Okay - sorry about this post, I couldn't resist. This is from Dr Russell at Kettering, who is an expert on this.
Collisions and the Conservation of Momentum
The impact between bat and ball is a collision between two objects, and in its simplest analysis the collision may be taken to occur in one-dimension. In reality most collisions between bat and ball (especially the ones I am able to make) are glancing collisions which require a two-dimensional analysis. It turns out, in fact, that a glancing blow is necessary to impart spin to the ball which allows it to travel farther.[5] Maybe I'll write about this more interesting, but more difficult problem later, but for right now I'll keep things simple and look at the collision in one-dimension only. The ball, m1, and bat, m2, both have initial velocities before the collision (subscript "b"), with the ball's velocity being negative. After the collision (subscript "a") both bat and ball have positive velocities. The before and after velocities and the masses of bat and ball may be related to each other through the physical relationship known as the conservation of linear momentum. Linear momentum is the product of the mass and velocity of an object, p=mv. If the net force acting on a system of objects is zero then the total momentum of the system is constant. While the bat and ball are in contact the player is exerting a force on the bat; the force needed to swing the bat. So, in a completely correct analysis, momentum is not constant because of this force exerted by the player swinging the bat. However, the force on the bat by the player is very much smaller than the forces between bat and ball during the collision, and the contact time between ball and bat is very short (less than 1 millisecond). This allows us to ignore the force on the bat by the player during the collision between ball and bat without significantly affecting our results. If we ignore the force by the player on the bat, we can express the conservation of linear momentum by setting the total momentum before the collision equal to the total momentum after the collision.
m1v1b + m2v2b = m1v1a + m2v2a
Usually when a student encounters the conservation of momentum in a physics course the masses of both objects are given, along with the initial velocities before the collision. A typical homework or quiz question would be to determine the final velocities of the two objects after the collision. When one is searching for two unknown quantities one must have two equations. So, we need more than just the conservation of momentum. For our student in a physics course this second equation is usually the conservation of energy. The conservation of energy relates the change in kinetic energy (associated with motion), the change in potential energy (associated with springs and position), and any work done by nonconservative forces (like friction) which act on the system. The change in kinetic energy includes information about the velocities of the ball and bat before and after the collision. During the collision the ball undergoes a significant amount of compression, and damping forces convert much of the ball's initial kinetic energy into heat. The change in potential energy and work done by friction describe how much of the initial energy is lost during compression of the bat and ball. The manner in which these energies are related during the bat-ball collision is rather complicated. However, the effective relationship between the elastic properties of the ball and the relative velocities of bat and ball may be summarized in terms of the coefficient of restitution, (e)
The coefficient of restitution of a baseball or softball decreases with increasing incoming ball speed (v1b). Modern baseballs are manufactured to have a coefficient of restitution of 0.55 for a 90mph pitch speed, while softballs are manufactured to have e=0.44 for pitch speeds of 60 mph. Assuming a constant pitch speed, we can combine two equations above and do a little algebra to solve for the velocity of the baseball after the collision:
This equation tells us how the batted ball velocity (v1a)depends on the mass of the ball (m1) and bat (m2), the elasticity of the ball (e), the pitched ball speed (v1b) and the bat swing speed (v2b). The properties of the ball may be treated as constants since they don't change during a turn at bat. The hitter has no control over the pitched ball speed, and while it may vary considerably from pitch to pitch we'll assume that it is a constant. The only two remaining variables which determine the final velocity of the ball are the mass of the bat, m2 and the initial speed of the bat, v2b. If we know these two parameters, we can predict the batted ball speed. As we will see, however, the problem is complicated somewhat by the fact that the speed with which a player can swing a bat depends on the weight of the bat.
Still confused? Wait there is more....
There is a big problem with the discusison of bat weight that I have summarized in this article. All of the physics used to derive the optimum mass and the batted ball speed assume that the ball hits the bat at its center-of-mass. This very rarely happens - hits at the sweet spot are several inches from the center-of-mass. There is another very important parameter of the bat which affects how quickly you can swing a bat, and what the final ball speed is. This parameter involves the distribution of mass along the length of the bat and how that mass distribution affects the motion of a rotating object. In physics we refer to this parameter as the moment of inertia. It turns out that the moment-of-inertia (or "swing weight") matters more than mass..