1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to determine energy required to hold an object in air

  1. Dec 21, 2007 #1
    For me to hold a heavy object stationary in air is tough and eventually I will get tired. So it seems I am expending energy. But then how much? I discovered it was quite hard (for me anyway) to calculate how much energy it costs to hold the object when there is no work.

    The only thing I could come up with requires knowledge about the system that is creating the force that opposes gravity. I suppose if you can determine how much power is going into the system and how much is going out then the difference is what it costs (J/s) to create the force to hold the object per unit of time.

    Is this really the only way to do it? It seems like there should be a better way because this is more like an efficiency calculation and I know different system would require different amounts of energy (per unit of time) to create the same force.

    I have a hunch I am missing something fundamental or making a mistake in my reasoning. Am I right?
    Last edited: Dec 21, 2007
  2. jcsd
  3. Dec 21, 2007 #2


    User Avatar
    Homework Helper

    The matter of the fact is that there is _no_ work being done when an object is just being suspended in mid-air. The feeling of expending energy is purely a biological concept, because in order to lift something we must displace our own bodies from its "equilibrium" (e.g. to stay upright and such). So yes, there is energy being expended, but none of that energy is really being transferred anywhere (not into the weights your carrying as their speed and gravitational potential remain the same), other than into heat as you sweat holding those weights up.

    Would you expend more energy holding weights arms straight in front of you or just by tying them over your shoulders? If there's a discrepancy, would you owe it to the laws of physics or the mechanics/biology/anatomy of your body?
  4. Dec 21, 2007 #3
    Human muscles work not like machines. Let say a crane holds a mass in the air, it does no work, no enery lost. But if a man hold something off the ground, he creates work, the work turns into heat. The muscle works by continuous contraction of many many small cells that requires energy (probably chemical energy) and exhausts heat.
    Sorry I do not know exactly how the muscle cells work.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook