The discussion revolves around the differences and applications of three fundamental physics formulas related to moving objects: F = ma (force), Ke = 1/2mv² (kinetic energy), and p = mv (momentum). Participants explore how these concepts relate to real-world scenarios, particularly in the context of baseball physics.
Participants generally agree on the definitions of the formulas but express differing views on the relevance of force in practical applications, particularly in sports contexts. The discussion remains unresolved regarding how to calculate force in specific scenarios, with multiple perspectives presented.
Participants highlight limitations in understanding how to apply the formulas in real-world situations, particularly regarding the definitions of acceleration and the conditions under which F = ma applies. There is also mention of the difficulty in measuring forces during brief collisions.
This discussion may be useful for beginners in physics, sports enthusiasts interested in the mechanics of ball dynamics, and individuals seeking clarification on the application of fundamental physics formulas.
axmls said:One of them relates an object's acceleration to the force applied on it, another gives the kinetic energy of a moving object, and the third is the momentum of a moving object.
beginner952 said:Thank you. I understand that much. What I don't understand is how they are used. For instance; I am a baseball fan and I am interested in the basic physics of bat and/or ball movements and force. If a ball is moving at 90mph and weighs 5 ounces it has 20250 of Kinetic energy. It has 450 of momentum. How are these used to determine Force? If at all. And where does the "a" in F= ma come from?
You cannot. And, in the usual case, the force is irrelevant. What you care about is the coefficient of restitution.beginner952 said:What I'm asking is how do I determine the force that will be applied to a stationary ball sitting on a tee, if the bat has 20250 of Ke and 450 of momentum?
OK. How do I calculate that? And, on the show Sports Science, and in books I've read, they talk about the ball hitting a wall with "x" amount of force. What are they talking about, and how did they determine that?jbriggs444 said:You cannot. And, in the usual case, the force is irrelevant. What you care about is the coefficient of restitution.
Sports Science is a joke. Force is not the almighty be all and end all of measurements that it is made out to be in such shows. It takes no particular strength and skill to generate multiple tons of force with a hammer and an anvil -- though the resulting force will be brief.beginner952 said:OK. How do I calculate that? And, on the show Sports Science, and in books I've read, they talk about the ball hitting a wall with "x" amount of force. What are they talking about, and how did they determine that?
Ok, thank you, I'm learning. So, when does F = ma apply? And how is "a" determined? If the ball is traveling at a constant rate of 90mph is "a" = 90? I'm having difficulty understanding F = ma.jbriggs444 said:Sports Science is a joke. Force is not the almighty be all and end all of measurements that it is made out to be in such shows.
The coefficient of restitution is determined by experiment. You bounce a ball off a golf club head at right angles and see what fraction of the initial energy is present after the rebound. This will usually be reasonably constant over a range of collisions. Given the impact velocity, head mass, impact angle and the coefficient of restitution, you can compute how the ball will move after the collision. You never have to know the force of impact.
beginner952 said:Ok, thank you, I'm learning. So, when does F = ma apply? And how is "a" determined? If the ball is traveling at a constant rate of 90mph is "a" = 90? I'm having difficulty understanding F = ma.
I'm confused. The kinetic energy in the moving bat applies a force to the ball, which makes the ball accelerate. But, my question is; how much force is the bat applying to the ball? How does one calculate how much force is needed to make a given mass accelerate, or gain momentum? If the ball weighs 5 ounces how much force is needed to make it move? 5 times "a" = F. I don't know what "a" is, so how do I get F?axmls said:The a is the acceleration of the ball for the duration that the force is applied. That is, if you hit a ball with a bat, while the bat is pushing the ball, a force is applied, and while the force is applied, the ball accelerates. The ball stops accelerating when the force is no longer applied. An acceleration is a change in velocity, so the force increases the velocity of the ball (accelerates it), and when the ball flies off the bat, it does so at a constant velocity, since the force is no longer acting on it.
You also need to know that acceleration ≠ velocity. Acceleration is the change in velocity per unit amount of time.beginner952 said:I'm confused. The kinetic energy in the moving bat applies a force to the ball, which makes the ball accelerate. But, my question is; how much force is the bat applying to the ball? How does one calculate how much force is needed to make a given mass accelerate, or gain momentum? If the ball weighs 5 ounces how much force is needed to make it move? 5 times "a" = F. I don't know what "a" is, so how do I get F?
"a" acceleration -- the rate of change of velocity over time. If you have a change in velocity that occurs over a brief time interval then the acceleration will be correspondingly large. The shorter the interval, the larger the acceleration. Accordingly, the shorter the interval the larger the force.beginner952 said:I'm confused. The kinetic energy in the moving bat applies a force to the ball, which makes the ball accelerate. But, my question is; how much force is the bat applying to the ball? How does one calculate how much force is needed to make a given mass accelerate, or gain momentum? If the ball weighs 5 ounces how much force is needed to make it move? 5 times "a" = F. I don't know what "a" is, so how do I get F?