Helicopter in a box: Third law

In summary: I: Crime Scene Investigation:In summary, the scale reading would change depending on the method of thinking used. If someone thought of the helicopter as having an impulse, the scale reading would change at lift off and then return to its original reading once the helicopter reached equilibrium.
  • #1
PeterPumpkin
34
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A thought-experiment. (This is not homework!) Supposing someone puts a radio-controlled helicopter in a CLOSED clear-plastic box. They then put the box plus chopper on a sensitive scale and recorded the weight. Say 50N for the sake of argument. Now suppose they started up the chopper and instructed it to hover in the center of the box. How would the scale reading change?

1) If I think in terms of internal forces, there should be no changes --- all internal forces balance. It should remain at 50N.

2) But if I think in terms of impulses I would expect the scale reading to change at lift off and then return to its original reading of 50N.

What am I missing? I wonder if anyone has actually done this.
 
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  • #3
I believe you are right that it would change at liftoff - the helicopter is accelerating upwards, causing an upwards acceleration in the overall center of mass of the system, increasing the force against the scale at liftoff. However, once the helicopter reaches an equilibrium (hover), the force against the scale will go back to precisely what it had been prior to the liftoff.
 
  • #4
PeterPumpkin said:
A thought-experiment. (This is not homework!) Supposing someone puts a radio-controlled helicopter in a CLOSED clear-plastic box. They then put the box plus chopper on a sensitive scale and recorded the weight. Say 50N for the sake of argument. Now suppose they started up the chopper and instructed it to hover in the center of the box. How would the scale reading change?

1) If I think in terms of internal forces, there should be no changes --- all internal forces balance. It should remain at 50N.

2) But if I think in terms of impulses I would expect the scale reading to change at lift off and then return to its original reading of 50N.

What am I missing? I wonder if anyone has actually done this.

It's been done:

http://mythbustersresults.com/episode77

CS
 

1. What is the third law of helicopter in a box?

The third law of helicopter in a box states that for every action, there is an equal and opposite reaction. This means that when a helicopter's rotor blades spin in one direction, it creates a force that pushes the air downwards, causing the helicopter to lift up in the opposite direction.

2. How does the third law of helicopter in a box affect the movement of the helicopter?

The third law of helicopter in a box is what allows a helicopter to move vertically. As the rotor blades spin, they create lift by pushing air downwards and this lift force is equal to the weight of the helicopter. This enables the helicopter to hover in place or move up and down.

3. Can the third law of helicopter in a box be applied to other forms of flight?

Yes, the third law of helicopter in a box is a fundamental principle of flight and can be applied to other forms of flight such as airplanes, rockets, and even birds. It explains how these objects are able to move through the air by creating lift and thrust.

4. How does the third law of helicopter in a box relate to Newton's laws of motion?

The third law of helicopter in a box is a specific example of Newton's third law of motion which states that for every action, there is an equal and opposite reaction. This law helps to explain how forces interact with each other and how objects are able to move.

5. Are there any limitations to the third law of helicopter in a box?

While the third law of helicopter in a box is a fundamental principle of flight, there are limitations to its application. For example, in order for a helicopter to generate lift, the rotor blades must be able to push against a medium, such as air. This means that in a vacuum, a helicopter would not be able to fly using this principle alone.

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