# Force of Wind on a moving object.

• marknixon
In summary, the problem is to calculate the force of windspeed on a moving object with a surface area while taking into consideration the weight of the object and its ability to support itself. The drag equation is used to calculate the force, but the drag coefficient may be difficult to determine. The weight of the carriage has no effect on the air resistance force, but it may affect the object's stability. The velocity of the object and wind should be added together when inputting into the drag equation, and for a monorail, the limitations of sideways force that the monorail can handle should be considered.
marknixon
Hi All,

I have a problem in which I am trying to calculate the force of the windspeed, x, on a surface area of a moving object, y.

I am applying this to a monorail model, where a monorail carriage (lets for this purpose assume its a rectangular box) with a surface area on one side is y, is traveling at s km/h, with a direct crosswind speed of x.

I am trying to ascertain if a) the weight of the carriage is important in finding out the total sideways force. We can assume that the monorail can support itself in regards to downwards force, but I am trying to find out the sideways force applied to the carriage.

If I have missed anything feel free to add your input - I only have high-school grad level physics knowledge!

Mark

You're looking to calculate drag. Here's the equation and an explanation of how to use it: http://www.grc.nasa.gov/WWW/K-12/airplane/drageq.html

The problem you will run into is that the drag coefficient is very difficult to calculate so you'll probably need to research and find typical drag coefficients for trains.

marknixon said:
Hi All,

I have a problem in which I am trying to calculate the force of the windspeed, x, on a surface area of a moving object, y.

I am applying this to a monorail model, where a monorail carriage (lets for this purpose assume its a rectangular box) with a surface area on one side is y, is traveling at s km/h, with a direct crosswind speed of x.

I am trying to ascertain if a) the weight of the carriage is important in finding out the total sideways force. We can assume that the monorail can support itself in regards to downwards force, but I am trying to find out the sideways force applied to the carriage.

If I have missed anything feel free to add your input - I only have high-school grad level physics knowledge!

Mark
The weight of the carriage has zero effect on the force from the air resistance - or wind.

However it is more likely the object will tip over if the position of its centre of mass is very low. But it's less likely to loose it's desired trajectory (it'll stay on the rail) if the mass of the object is very large.

So the drag equation is D = Cd x ((P x V^2)/2) x A

With V^2 (Velocity squared) do take the sum of the wind speed and carriage speed? i.e. if wind and carriage are same direction, addition, and if in opposite directions, subtraction?

The weight of the carriage will be high, maybe up to 30 tonnes. As it on a monorail I will need to find specifically the limitations on sideways force applied to the carriage that the monorail can handle. Does anyone know how I would be able to calculate this 'sideways' force due to the wind? Would I use the drag model again?
Thanks
Mark

At 30 tonnes I doubt the air resistance is going to have much effect on the behaviour of the carriage.

But yes, add the velocities together, they're vectors them insert in the equation. ie If your traveling forward at 100km/hr and you have a 100km/hr tail wind, the force from air resistancwe would be just zero. If you had a head wind of 100km/hr then V is effectively 200km/hr (that's V = 27.78m/s).

## 1. What factors affect the force of wind on a moving object?

The force of wind on a moving object is primarily affected by the speed and direction of the wind, the shape and size of the object, and the density of the air. Other factors such as surface roughness and air temperature can also play a role.

## 2. How does the shape of an object affect the force of wind?

The shape of an object can greatly impact the force of wind on it. Objects with streamlined shapes, such as airplanes, experience less drag and therefore less force from the wind compared to objects with irregular or flat shapes.

## 3. Does the speed of the wind affect the force on a moving object?

Yes, the speed of the wind is a major factor in determining the force on a moving object. As wind speed increases, so does the force it exerts on the object. This is why strong winds can cause more damage to structures and vehicles.

## 4. How does the direction of the wind impact the force on a moving object?

The direction of the wind can either increase or decrease the force on a moving object. When the wind is blowing in the same direction as the object's motion, it can provide a tailwind and decrease the force. However, when the wind is blowing in the opposite direction, it creates a headwind and increases the force on the object.

## 5. Can the force of wind on a moving object be accurately predicted?

While there are mathematical equations and models that can predict the force of wind on a moving object, it can be difficult to accurately predict in real-world scenarios due to the many variables involved. Factors such as turbulence, gusts, and wind direction changes can all impact the force on a moving object.

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