Finding the wind-resistance force

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Discussion Overview

The discussion revolves around calculating the wind-resistance force acting on a bullet fired by a sniper, considering various factors such as initial speed, distance to the target, wind speed, and the bullet's drop due to gravity. The scope includes theoretical calculations and considerations of projectile motion, drag forces, and the impact of wind on the bullet's trajectory.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants propose calculating the wind-resistance force using the drag equation, which involves the drag coefficient, air density, and cross-sectional area of the bullet.
  • One participant notes that even without considering air resistance, the bullet will drop significantly due to gravity over the time it takes to reach the target, raising concerns about the feasibility of hitting the target within the specified drop limit.
  • Another participant discusses the need for vector addition to account for the opposing wind velocity when calculating the effective horizontal velocity of the bullet.
  • There is mention of the complexity introduced by drag force, which decreases as the bullet's velocity reduces, complicating the calculations.
  • One participant suggests that the parameters provided may be inconsistent or erroneous, indicating a need for clarification or correction.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of hitting the target given the constraints of bullet drop and wind resistance. There is no consensus on the calculations or the assumptions made regarding the parameters involved.

Contextual Notes

Limitations include the assumptions made about the bullet's trajectory, the accuracy of the parameters provided, and the complexity of calculating drag force as the bullet slows down. The discussion does not resolve these issues.

Who May Find This Useful

This discussion may be of interest to those studying projectile motion, ballistics, or fluid dynamics, as well as individuals interested in the effects of environmental factors on projectile trajectories.

ChessEnthusiast
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Imagine such situation:

There is a sniper who fires his rifle, the bullet travels at the initial speed of, say, 1400 m/s. His target is standing 2000 meters away and the wind is blowing at 30 m/s opposing the bullet's motion. Let's assume that the bullet is fired in a straight lane and it may fall the maximum of 0.5 m to still hit the target.
After how many seconds (if at all) will the target be hit?
Let's also assume that the cross-sectional area and the drag coefficient of the bullet is known.

Is there a way to calculate the force the wind will be opposing the motion of the bullet with?
 
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ChessEnthusiast said:
Imagine such situation:

There is a sniper who fires his rifle, the bullet travels at the initial speed of, say, 1400 m/s. His target is standing 2000 meters away and the wind is blowing at 30 m/s opposing the bullet's motion. Let's assume that the bullet is fired in a straight lane and it may fall the maximum of 0.5 m to still hit the target.
After how many seconds (if at all) will the target be hit?
Let's also assume that the cross-sectional area and the drag coefficient of the bullet is known.

Is there a way to calculate the force the wind will be opposing the motion of the bullet with?
Even ignoring air resistance, we have a problem. 2000 meters at 1400 meters per second will take longer than one second. In one second, a bullet will drop 4.9 meters (##\frac{1}{2}gt^2## where g = 9.8 m/sec2) due to gravity. But you have imposed the requirement of a maximum 0.5 meter drop.

Edit: Drop from a bore-sighted, straight-at-the-target launch angle may not be what you are after. One can correct for that by aiming high. Instead, you may be constrained by the arch -- how much higher the mid-point of the trajectory is than the midpoint of the straight-line path. Ideally, that difference is lower by a factor of four. But that is still well over 0.5 meters.
 
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If by straight line,l you mean horizontally, then range R=ut where u is initial velocity and t is time. Since the wind is directly against u, then you use vector addition. V= u+(-s) = 1400–30= 1370, where s is velocity of the wind. Now, in a projectile motion V(horizontal velocity) is constant neglecting drag. However, drag force is involved, therefore F=1/2C¶AV^2 where C is drag coefficient, ¶ is air density, and A is cross-sectional area. Remember that V was to move in a constant motion but since F is involved, it brings it to rest gradually.
Then F=(mV–m0)/t° = mV/t°. The time t can be computed.
Now from R=ut, 2000=1370t, t=2000/1370(time without drag force)
Finally, if t° >> t, or t°<t, then it can't hit the target. The reason is because
1) drag force reduces as the velocity reduces, making its calculation more complex. Nevertheless, this calculation should be a good estimation.​
2) The velocity turning to Zero is impractical since gravity will pull the bullet down to make impact with the ground.
For the force of the wind on the bullet,
F=m(2000–1370)/t`, if only we knew t`. This is different from wind resistance. The wind resistance(Air Friction) is just the drag force.

But it seem that your parameters are inconsistent and erroneous, however, assumed they were correct.
 
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