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Deep Thought
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I think I understand this concept but wanted to get other opinions. My son and I are Taekwondo Black Belts and have to break boards occasionally. My son frequently has trouble breaking his and this got me thinking about the physics aspect of board breaking.
I know that the force applied to the board in a strike is F=ma where the body is the mass and the acceleration is the velocity change of the punch. (This example assumes the punches are parallel to the ground). If he tries to strike the board and reaches constant velocity before impact then the force should be zero since acceleration is zero. Additionally, the force could be negative if he pulls the punch so that it is slowing (decelerating) before impact. This just seemed counter-intuitive that the force is 0 since it certainly doesn't feel like a zero force impact.
After thinking about this, my conclusion is that when the force = 0, then the board exerts the same force as the punch resulting in a net of 0. If the force is negative then the energy of the punch (which is not the same as force) is transmitted back to hand by the board (which is why it hurts). Only by creating a positive force that exceeds the breaking strength of the board through punch acceleration can the board be broken.
Do I have this analysis correct?
Thanks!
Deep Thought
I know that the force applied to the board in a strike is F=ma where the body is the mass and the acceleration is the velocity change of the punch. (This example assumes the punches are parallel to the ground). If he tries to strike the board and reaches constant velocity before impact then the force should be zero since acceleration is zero. Additionally, the force could be negative if he pulls the punch so that it is slowing (decelerating) before impact. This just seemed counter-intuitive that the force is 0 since it certainly doesn't feel like a zero force impact.
After thinking about this, my conclusion is that when the force = 0, then the board exerts the same force as the punch resulting in a net of 0. If the force is negative then the energy of the punch (which is not the same as force) is transmitted back to hand by the board (which is why it hurts). Only by creating a positive force that exceeds the breaking strength of the board through punch acceleration can the board be broken.
Do I have this analysis correct?
Thanks!
Deep Thought