Effects of wind on a moving person

[ForecasterJason]

Hi,
I am curious as to the effects of wind on a moving person. If a person is walking at 4 mph and they encounter a 10 mph headwind, would the person feel the wind about the same as if he/she is standing still and is facing a 14 mph headwind? Likewise, if a person is running at 7 mph and encounters a 20 mph tail wind, should the wind feel about the same as a 13 mph tail wind if this person were standing still? I'm guessing there may be other factors that could complicate the calculations, but I'm wondering if these simple calculations could be approximately correct.

Also, is there a way to approximate how a cross wind would feel to a moving person?

Thanks

 

[Grinkle]

If a person is walking at 4 mph and they encounter a 10 mph headwind, would the person feel the wind about the same as if he/she is standing still and is facing a 14 mph headwind? Likewise, if a person is running at 7 mph and encounters a 20 mph tail wind, should the wind feel about the same as a 13 mph tail wind if this person were standing still?

Yes.

Also, is there a way to approximate how a cross wind would feel to a moving person?

If the wind is at right angles to the person's movement, the magnitude of the push is exactly the speed of the wind.

 

[anorlunda]

The answers to headwinds and tailwinds are yes. I'm a sailor, and I experience those feelings every time I go sailing.

Most dramatic. If your boat moves forward at 5 knots, with a 5 knot tail wind, you experience zero wind. If the tail wind was 10 knots, then you feel the wind passing you from behind.

Yes you do feel cross winds, but I don't know how to interpret your question. But there is a thing called apparent wind, which is the wind you feel based on the combination of your motion and the wind speed and direction.

 

[A.T.]

If the wind is at right angles to the person's movement, the magnitude of the push is exactly the speed of the wind.

No it isn't.

 

[FactChecker]

You should do the vector calculation and work with the relative wind. This is the "True wind" described above by @anorlunda .

CORRECTION: The relative wind is the "Apparent wind" described above by @anorlunda .

 

[ForecasterJason]

Thanks everyone. The apparent wind was what I meant by cross winds, and I found out how to calculate the speed for that.

 

[Grinkle]

No it isn't.

Ooops. I was thinking about a treadmill or a person on a sidewalk that is pushed by the wind but not actually having their course altered by the wind when I said that.

 

[A.T.]

Ooops. I was thinking about a treadmill or a person on a sidewalk that is pushed by the wind but not actually having their course altered by the wind when I said that.

That's irrelevant, your statement would still be wrong. Draw a vector diagram for the situation like the ones above.

 

[Grinkle]

That's irrelevant, your statement would still be wrong. Draw a vector diagram for the situation like the ones above.

Not sure what I'm missing. Below is meant to be a back or front view of me walking on a treadmill with a fan at 90 degrees to the treadmill. The reaction force that keeps me from sliding off the treadmill sideways seems to me independent of what speed the treadmill is set to, and only dependent on the fan power.

 

[A.T.]

Not sure what I'm missing. Below is meant to be a back or front view ...

Try a top down view, with all the velocity vectors. And what does a treadmill have do with all this? Just have someone walk on the sidewalk.

 

[anorlunda]

Not sure what I'm missing. Below is meant to be a back or front view of me walking on a treadmill with a fan at 90 degrees to the treadmill. The reaction force that keeps me from sliding off the treadmill sideways seems to me independent of what speed the treadmill is set to, and only dependent on the fan power.

View attachment 105478

The vector diagrams in #3 apply to you as much as to a boat. They also apply if the magnitude of true wind is zero.

Remember, your speed is the direction your body moves, not the way your nose is pointing. You can rotate your body to any angle relative to your motion.

 

[Grinkle]

A treadmill generates no headwind in still air, so its easier for me to visualize all of the forces.

If I am standing still, its even easier to picture, or even easier to overlook whatever I am overlooking.

If I am standing still and a fan turns on to my right, I am pushed to the left by whatever force the fan wind is hitting me with.

Now, if a second fan is turned on directly ahead of me, I can't see how that changes the force that is pushing me to the left. They are perpendicular to each other.

If I start walking forward towards the fan in front of me, I increase the headwind force but I still can't see how I am changing the cross-wind force with my motion that is perpendicular to the cross wind.

I will draw some more diagrams and keep thinking about it.

 

[Grinkle]

Remember, your speed is the direction your body moves

This is why my intuition tells me a situation involving static forces in one direction is different that a situation where motion is not constrained in any direction. That is what I meant when I said

Ooops. I was thinking about a treadmill or a person on a sidewalk that is pushed by the wind but not actually having their course altered by the wind when I said that.

Are they not different?

 

[A.T.]

A treadmill generates no headwind in still air, so its easier for me to visualize all of the forces.

Boats aren't running on treadmills. It's not about what is easier for you, but what is right.

 

[Grinkle]

The OP wasn't asking about a boat. The question was -

I am curious as to the effects of wind on a moving person. If a person is walking at 4 mph

 

[anorlunda]

The OP wasn't asking about a boat. The question was -

The same vector diagrams work for a boat, a person, an airplane, or any object.

 

[A.T.]

The question was -

And where is a treadmill in that question?

 

[Grinkle]

The same vector diagrams work for a boat, a person, an airplane, or any object.

Certainly. I am either very dense or failing to communicate well or both.

If a boat drops anchor, the boat speed goes to zero and the apparent wind becomes equal to the true wind. Is that not the case?

If that is the case, then a person walking on a sidewalk is anchored in the axis perpendicular to the sidewalk, is my thinking.

If that is not the case, then I am really confused.

 

[Grinkle]

And where is a treadmill in that question?

I agree, no treadmill. I tried to remove that from my thinking.

If I am standing still and a fan turns on to my right, I am pushed to the left by whatever force the fan wind is hitting me with.

Now, if a second fan is turned on directly ahead of me, I can't see how that changes the force that is pushing me to the left. They are perpendicular to each other.

If I start walking forward towards the fan in front of me, I increase the headwind force but I still can't see how I am changing the cross-wind force with my motion that is perpendicular to the cross wind.

 

[A.T.]

If a boat drops anchor, the boat speed goes to zero and the apparent wind becomes equal to the true wind. Is that not the case?

If that is the case, then a person walking on a sidewalk is anchored in the axis perpendicular to the sidewalk, is my thinking.

A moving person is equivalent to a boat at rest? Sorry, you don't make any sense to me.

 

[Grinkle]

A moving person is equivalent to a boat at rest? Sorry, you don't make any sense to me.

A person walking on a sidewalk and not slipping will not be moved by a crosswind (or any wind, as long as they are not slipping). I am drawing an analogy to an anchored boat being similarly prevented from being moved by the wind.

Picture a person on ice being blown sideways by a fan, and change the picture to a person standing still against the wind on a sidewalk being blown by a fan. The vector diagrams for these two situations a different. Do you agree?

 

[anorlunda]

Certainly. I am either very dense or failing to communicate well or both.

If a boat drops anchor, the boat speed goes to zero and the apparent wind becomes equal to the true wind. Is that not the case?

If that is the case, then a person walking on a sidewalk is anchored in the axis perpendicular to the sidewalk, is my thinking.

If that is not the case, then I am really confused.

You are confusing the forces acting on the person with whether those forces move the person or not. An airplane or a boat can navigate a straight path from point A to point B regardless of cross winds by simply adjusting the direction the nose points. It is incorrect to say that the plane/boat is anchored to the A-B line, they achieve it by compensating for the side forces.

 

[Grinkle]

You are confusing the forces acting on the person with whether those forces move the person or not.

Ah. I get it now, thanks. If I think of the static friction on a sidewalk as a self-adjusting engine then it clicks.

 

[A.T.]

A person walking on a sidewalk and not slipping will not be moved by a crosswind (or any wind, as long as they are not slipping). I am drawing an analogy to an anchored boat being similarly prevented from being moved by the wind.

The analogy is between a moving person and a moving boat. They will both experience the same apparent wind from a true 90° cross wind, but it's magnitude is not the same as the true wind.

 

[Grinkle]

They will both experience the same apparent wind from a true 90° cross wind

The piece I was missing I think is that to make situation equivalent I need to add an engine to the boat that prevents it from being moved in the direction of the crosswind. Then the vector diagrams become the same. Thanks for your patience.

 

[A.T.]

The piece I was missing I think is that to make situation equivalent I need to add an engine to the boat that prevents it from being moved in the direction of the crosswind.

Sail boats don't need engines for that, just a keel.

 

[Grinkle]

If the below is correct, then I get it. I was definitely confused.

edit: Which is just case c in the earlier post. Sigh.

 

[ForecasterJason]

So, something I've been thinking about lately is the effect of wind on long hair while someone is running. Since long hair will often bounce around up and down and side to side, is it predictable what the effects would be with a strong wind? Or would this be too complicated?

For example, suppose someone with long hair is running at 8 mph and encounters a 30 mph tail wind. Based on previous responses, I know that to the person it should feel like a 22 mph tail wind. But would the bouncing hair create any resistance to it being blown? In other words, would the hair still be blown forward like it would in a 22 mph tail wind if the person was standing still? And would a 30 mph head wind blow the hair back like a 38 mph wind standing still?

I'm guessing that a cross wind would be harder to predict if the hair is going side to side.

Also, how differing wind speeds and directions feel to someone who is riding a bike, and what it's doing to their hair, should be the same as if the person was walking, correct?

 

[sophiecentaur]

@Grinkle
If you assume the body is a vertical cylinder, do a vector addition of the walking velocity and wind velocity and find the resultant air speed. Then use the drag factor of a cylinder.
Drag Force Equation link
Drag Coefficient link
If the body is drastically non symmetrical around a vertical axis then it is harder to calculate because the two air flows cannot be considered as independent and you can't really just do a vector addition of the two forces and you would need to work out (or find out) the drag coefficient for the particular shape.

 

[ForecasterJason]

So, something I've been thinking about lately is the effect of wind on long hair while someone is running. Since long hair will often bounce around up and down and side to side, is it predictable what the effects would be with a strong wind? Or would this be too complicated?

For example, suppose someone with long hair is running at 8 mph and encounters a 30 mph tail wind. Based on previous responses, I know that to the person it should feel like a 22 mph tail wind. But would the bouncing hair create any resistance to it being blown? In other words, would the hair still be blown forward like it would in a 22 mph tail wind if the person was standing still? And would a 30 mph head wind blow the hair back like a 38 mph wind standing still?

I'm guessing that a cross wind would be harder to predict if the hair is going side to side.

Also, how differing wind speeds and directions feel to someone who is riding a bike, and what it's doing to their hair, should be the same as if the person was walking, correct?

Bumping to see if anyone can provide insight.

 

[sophiecentaur]

Bumping to see if anyone can provide insight.

Using long hair as the 'wind detector' is good because hair will just follow the direction of the apparent wind and not be affected too much by the body shape. Just add the two velocities (whatever angles they are at) and you will get the direction the hair will point in. Moving up and down at the same time could have an effect but it just depends on how far you want to take the accuracy; the vertical velocity would also come into the equation.

 

[ForecasterJason]

Using long hair as the 'wind detector' is good because hair will just follow the direction of the apparent wind and not be affected too much by the body shape. Just add the two velocities (whatever angles they are at) and you will get the direction the hair will point in. Moving up and down at the same time could have an effect but it just depends on how far you want to take the accuracy; the vertical velocity would also come into the equation.

Ok thanks. So, it sounds like then the speed as well with which it would be blown would be accurate from what I was saying.

 

[sophiecentaur]

the speed as well with which it would be blown

The reference frame direction needs to be considered here. Of course, the actual velocity of the hair is the same as that of the person. Apparent wind is what will govern the direction of the hair wrt the person and their direction of travel. This is no big deal - just something one needs to take into account. Sailors look at their wind indicator (on top of the mast) constantly but that only gives apparent wind but the flag on the nearby club house can give a different answer and also the flags on other yachts.

 

[ForecasterJason]

The reference frame direction needs to be considered here. Of course, the actual velocity of the hot is the same as that of the person. Apparent wind is what will govern the direction of the hair wrt the person and their direction of travel. This is no big deal - just something one needs to take into account. Sailors look at their wind indicator (on top of the mast) constantly but that only gives apparent wind but the flag on the nearby club house can give a different answer and also the flags on other yachts.

Ok. Did you mean "hair" in your second sentence?

 

[sophiecentaur]

Ok. Did you mean "hair" in your second sentence?

Proof reading rules ok.