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Speed, altitude, and horizontal distance

  1. May 22, 2015 #1
    I have thrown several things from balls to paper airplanes and I have noticed that the faster I throw something the longer it stays at any given altitude. The slower I throw something the shorter it stays at a given altitude.

    Also I have noticed that fast objects slow down faster than slow objects do. And fast objects tend to travel farther than slow objects.

    But why does something fast decelerate much faster than something that is slow. I would think that for the slow one it is easier to decelerate and so it would do it faster. I know it has something to do with the lift and drag forces as well as the amount of thrust my arm gives to the object.

    And if fast objects slow down faster then how is it that they travel farther?
  2. jcsd
  3. May 22, 2015 #2


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    Ask yourself: what is causing thrown objects, fast or slow, to decelerate in the first place?
  4. May 22, 2015 #3
    The forces of lift and drag being greater than the forces of thrust and gravity causes thrown objects to decelerate.
  5. May 22, 2015 #4


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    And how might the drag force change with the speed of the object being thrown?
  6. May 22, 2015 #5
    Drag will increase if thrust increases because of Newton's 3rd law
  7. May 22, 2015 #6


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    Newton's 3rd Law is dealing with action/reaction. That's not the case with thrust/drag.

    If a rocket in outer space has a thrust applied to it, is there a drag force created on the rocket?
  8. May 22, 2015 #7
    yes there is a drag force.
  9. May 22, 2015 #8
    No there is not
  10. May 22, 2015 #9
  11. May 22, 2015 #10
    Because the faster the object the greater the drag. That's why its faster to decelerate.
  12. May 22, 2015 #11
    No. I can travel at 5000 mph in space and feel no (negligible) drag.

    Hint: read the wikipedia article about what causes drag.
  13. May 22, 2015 #12
    Lift can cause drag and so can friction and even gravity. Gravity drag is the kind of drag a rocket has as it goes up the atmosphere. Lift causes drag because the higher up you go the more force you need to get to that altitude. Friction always causes drag and is what causes most of the drag in a thrown object. The more thrust there is the more friction with the air there is. The more friction there is the more drag there is at any given altitude.
  14. May 22, 2015 #13


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    What happens to the drag when you run out of air?
  15. May 22, 2015 #14
    The friction drag gets very small. It still exists though because of high energy atoms and photons. The lift drag also decreases but not as much. The gravity drag also gets very small because of there being very little gravity. So overall the total drag gets very small.
  16. May 22, 2015 #15
  17. May 23, 2015 #16
    Look here in the gravity drag article:


    Here it says that as an object is going straight up that gravity causes drag which makes sense since drag is opposite in direction to thrust and the thrust is in this case an upward force.

    Photons can cause drag. The reason? It is because as photons travel along a surface they act as a particle causing friction. However this is so miniscule that it is unnoticed. Even with gamma ray photons there still isn't any noticeable friction(which would be felt as heat) but there is enough friction that a scientific instrument could detect it.

    The only exception to this is infrared light because infrared light is heat and so the more infrared light there is, the hotter it is. The friction of the infrared light on your skin can be felt as heat on a sunny day.

    And why wouldn't newton's 3rd law apply to thrust and drag? They are 2 opposite forces and when you apply more thrust to an object that same object experiences more drag. Even with a design to minimize drag and maximize thrust drag still increases as thrust increases. It has to do so since it will rub against any particles in space or in air with more energy. There is just no way to make drag decrease as thrust increases. This is not a violation of newton's 3rd law.
    Last edited: May 23, 2015
  18. May 23, 2015 #17
    Gravity is a force. Drag is a result of moving other objects, such as air particles. At least it is so in the common parlance.

    I won't comment on your treatment of light and heat, as at least at my level it seems like utter rubbish.

    What if there are no other particles in space? No drag. So you can make drag decrease although the thrust is increasing: by removing the other particles, i.e. going into a vacuum. QED.

    Please, can someone with more credibility weight in so I can either revise my understanding of things, or this thread can be put to rest?
  19. May 23, 2015 #18


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    The answer is simply that drag increases as speed increases. The ease at which something can be accelerated is found by the formula: F=MA. Rearranging this we get A = F/M. So when the force (drag) is high, the rate of acceleration is as well. Note that there is no reason to bring up thrust in your example, as we are only talking about the acceleration of the object after it is released from your grip, so there is no more accelerating force pushing it forward, there is only the decelerating force of drag.

    Pretty much everything you've said here is simply wrong. Gravity drag is not the same effect as aerodynamic drag at all. Photons do not cause drag either. Infrared light is not heat any more or less than gamma rays are and IR light certainly doesn't heat your skin up because of friction.

    The original question was answered back in post #10 and since then the thread has gone off the rails. Thread locked.
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