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  • Users: Pkruse
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  1. P

    Punch speed and exerted g's

    The impulse delivered in a punch has very little to do with the speed or acceleration of the fist, and much more to do with what the puncher does with the rest of his/her body. A trained person can do much more damage with an elbow strike than with a punch, yet the speed and acceleration of the...
  2. P

    How does a shock absorber work or should work?

    I find it interesting to get engineers and physicists involved in the same discussion. One is concerned with the pure science, while the other with practical application. As an engineer I use the science to the extent that it is useful, as often it is. But other times I do stuff simply...
  3. P

    Skydiver balloon

    Could fill it with Hydrogen, which is lighter than Helium. The balloon will not burst at the desired height because it is designed with enough surplus capacity to contain the gas after it expands.
  4. P

    How does a shock absorber work or should work?

    The really nice thing about viscous damping is that it is linear. Friction damping is called Coulomb damping. An example is found commonly in a washing machine to damp out the drum during the spin cycle. Another is the anti sway mechanism in a trailer hitch to prevent a trailer from fish...
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    How does a shock absorber work or should work?

    There are many types of shock absorbers in many types of mechanical designs. All have one thing in common, which is that they absorb energy. The viscous damping you site absorbs energy by heating oil. Other EA systems absorb by friction, or by deforming material, or by tearing it. A common...
  6. P

    Difference between the amount of water displaced by a floating vs submerged object?

    For a submerged object, the volume of water displaced is equal to the volume of the object. For a floating object, it will displace a water weight equal to the object weight. So you don't need to know the density of the object, except to verify if it is greater than or less than the density of...
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    Why did my compass work perfect at the store but stop working soon as I got home?

    Before taking it back, you might take it away from home to see if it works. You many have some sort of magnetic anomaly at home.
  8. P

    Designing pressure vessels that split.

    I don't understand what perceptions you refer to. I've been on the investigation team after a pressure vessel split. These were cylinders, some with water, some oil, and one pneumatic. In all cases, the witnesses said they exploded. Of course, the pneumatic vessel ruptured with much more...
  9. P

    Designing pressure vessels that split.

    The normal approach is to design it so that it does neither. That is what applicable codes and standards are all about.
  10. P

    Why does a ball rebounds more over the edges?

    If the table and the ball were rigid bodies, bounce would be the same. In this case, I suspect that the middle of your table has less stiffness and more ability to absorb energy. Another table may behave differently.
  11. P

    I have a question about pulley

    Google images for a block and tackle, or a mobile crane block. Once you see one rigged up your answer should be self evident.
  12. P

    String Forces and pulleys

    If someone can rig up a system of pullies, then we can write the equations for that system. Why don't you suggest an example?
  13. P

    How much force would it require to obliterate a baseball bat?

    It would be fairly easy to calculate breaking force for a slowly applied load. But an impact of very short duration greatly complicates matters. Hence the need for empirical measurements.
  14. P

    Buoyancy of object in water

    I've designed many many buoyant systems for seawater. If figure volume in cubic feet and multiply by 60 lbf per cubic foot. The water is a little heavier than that, but I like the margins in case my material absorbs a little water.
  15. P

    Weight in an elevator, at terminal velocity

    Nobody is going to float like astronauts in an elevator because an elevator's design makes it physically impossible to free fall. The counterweight typically weighs a little more than the elevator, so if all control mechanisms were to let loose, the counterweight would fall down and the...
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    Centrifugal Force Explosion

    To answer your other question, you are not creating any energy. You have an energy supply, probably the power grid. You are transferring it into kinetic energy to make the disk spin. When the disk breaks, that energy is now in the form of metal fragments flying in random directions at high...
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    Centrifugal Force Explosion

    If you spin a steel disk fast enough to fail the steel, it will be a very high energy explosion. This test has often been done in the past on gas turbine disks in a spin pit.
  18. P

    Propeller rotation direction question

    I've seen this on engines as small as 120 HP. But all my experience is with diesils. Sometimes I forget that they put gas engines in boats.
  19. P

    Why water turbine have higher efficiency then steam turbine?

    May not be true any more since they had to slow them down to protect the baby fish.
  20. P

    Propeller rotation direction question

    Many marine engines are sold in right and left configurations, and can be easily converted from one to the other. A few are kluged up to make the change in the gear box, but each engine has its own box. I've also seen two engines turning in the same direction, but with the shafts mounted at...
  21. P

    Effective punch: muscles or speed?

    Speed and force are both important, but other things are more importamt if you want a knock out punch. You must hit the target at the right place and at the right angle. You must follow thru so that you continue to deliver force. Bruce Lee used to say never throw a punch at a man's face...
  22. P

    Run-on Torque value added to required torque for self-locking nut.

    If I require the tech to measure the run on torque in the field, it will only be to make sure that the self locking feature is still working. They do wear out after a number of repeated uses.
  23. P

    Run-on Torque value added to required torque for self-locking nut.

    From an engineer who specifies torque in tech manuals: you already have one good reply, so I'll add to that. If I call out a torque that means that I'm not terribly concerned about the preload. This is because a torque will result in a huge variation in actually preload. So I'll take that...