Force and speed describe different things but can both be measured in miles per hour (MPH). However, the conversion method is not the same for all types of objects and forces. Converting from force to MPH is not the same as converting speeds such as kilometres per hour to MPH, where a simple conversion ratio can be applied. A description of the conversion method from wind force exerted on a building to the estimated speed of the wind in MPH will illustrate the issues involved.
- Skill level:
- Moderately Challenging
Write the equation that describes the force of the object whose speed you want to determine. In the case of wind force, F= 0.5 * P * V^2 * A * Cd, where F is force, P is the density of air, V is the speed of the air, A is the area of the object receiving the blow of the wind and Cd is the drag coefficient.
Reorganise the equation so V, speed, is on its own on the left-hand side of the equation. In the example above, the resulting equation would be V^2 = 2F/ACd and V would be equal to the square root of 2F/ACd.
Measure the variables described in the equation you wrote in Step 1. In the example of wind force, you will need to measure the force of the wind, the density of air in your location, the area of the object receiving the blow of the wind and the drag coefficient of the object being blown. For instance, the drag coefficient of a flat plate is 1.28 and the density of air at sea level is 1.2 kilograms per cubic meter.
Substitute the values you found in Step 3 for the variables of the equation you reorganised in Step 2. For example, if the wind blowing on a flat plate at sea level is travelling with a force of 18003 Kilogram on an area of 14.30 square meters, we can use the equation we used in Step 2 to estimate the speed of the wind at 50 MPH.
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