Science in Sport. 106 How fast is the wind speed? Read. Count/Tachometer Any EASYSENSE. Sensors: Loggers: Logging time: EasyLog

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1 Sensors: Loggers: Count/Tachometer Any EASYSENSE Science in Sport Logging time: EasyLog 106 How fast is the wind speed? Read When an Olympic or world record is set, the rules for it to stand are quite strict. There has to be no slope on the running track, the track surface has to be of type and the wind speed has to be no more than a preset value. Most sports have some form of standardising / equalising regulations, wind speed is one variable that may affect performance that can be easily studied. Wind speed is found using an anemometer. The simplest variety is a set of identical cups attached to a rotor; the wind pushes against the cups and makes the rotor turn. Counting the number of rotations and knowing the dimensions of the anemometer allow the calculation of speed. The cup anemometer works well and is very reliable, but in some circumstances the use of a set of rotating cups is not realistic on a plane to record air speed for example. Other types of anemometer have been devised to be used where the spinning cup design is unsuitable. Planes use a Pitot tube, which uses variation in air pressure to calculate speed; ships or harsh weather environments use ultrasound to record speed. In this investigation you will be asked to create a simple cup anemometer and record the wind speed. If the air is very still you may need to use a desk fan to create an artificial wind for testing. The results from your device can then be compared to the results from a calibrated gold standard device. The importance of the gold standard is that all the devices should give the same speed, you need to have agreement. When your success or failure in a competition relies on technology you need to be confident with the reliability of the device. If you understand how the devices are all made to be the same, your desire to blame the technology may become reduced. Example anemometer designs, whatever the design the device should be freely rotating

2 What you need 1. An EASYSENSE logger. 2. Reference anemometer e.g. Data Harvest Anemometer. 3. A Smart Q Count/ Tachometer sensor. 4. A Smart Q Crocodile clip set. 5. Strong magnets. 6. Reed switches. 7. Disposable cups / beakers. 8. Wooden sticks /rods. 9. Corks 10. Pins, sticky tape, Blu-Tack 11. Desk fan What you need to do You need to make a device to record the wind speed (an anemometer). When you have made the device you need to calibrate it and check it has a constant accuracy across a range of speeds. There are many possible designs; most use a cross of a stiff material. The ends of the cups / blades are placed at the ends of the cross arms. A securing pin goes through the cross at its centre to both secure the arms in place and to act as a turning point. The device needs to be balanced to get the best rotation. It should be possible to construct a vane type windmill to give wind speed. Devices of this type do need to be pointed into the wind. The cup anemometer is not dependant upon wind direction. Plastics often form the best construction materials, they are light and strong. For the arms that will support the wind cups thin wooden dowel works well. Try to keep designs compact, and as light as possible, if more mass is used the inertia to rotate will become too high for the device to work. Once you have constructed a reliable anemometer you will want to collect readings from it. The simplest is to count the rotations per minute and use a calibration curve to convert to wind speed; while effective it is not very good for long term or remote logging. If you fix a switch to the rotor so that every rotation closes / opens the switch a pulse per rotation is created and can be counted. A simple switch to use is a magnet and a reed switch; this adds no resistance to the turning of the rotor. Fit the magnet to the rotor, this stops wires getting tangled. When fitting the magnet to the rotor you will need to balance the opposing arm with a similar mass. Ideally the magnet should be placed close to the turning axle to keep the centre of gravity in the pivot point. The reed switch will need to be placed no more than 5 mm from the magnet, the exact distance will depend on the strength of the magnet and the type of reed switch used. The fitting of the reed switch and magnet may well be the most difficult part of the exercise; you could always fall back to using the standard anemometer to find the wind speed at a distance from a fan. Once the speed of the airflow is known, the homemade versions can be calibrated by finding the number of revolutions per minute, 30 s, etc. Use a desk fan to provide a constant wind. You will find that placing the anemometer to one side will give the best air to move the cups, placing the anemometer square to the fan can lead to the forces on opposite cups being equal and any turning effect is neutralised

3 Setting up the software 1. Connect the crocodile clips to the reed switch on the homemade anemometer. Connect the crocodile clip set to an input on the logger. 2. Find the circumference of the anemometer you have made. You will need:- The distance from the turning point to the end of the arms of the apparatus. Value for pi. Formula for calculating circumference = C = 2 r or d. Where r = the radius of the circle and d = the diameter of the circle. Remember to keep the units constant; if you want the end result to be metres per then measurements should be in metres not cm. 3. From the EasySense software s Home screen select Graph. When the logging wizard starts select Finish. 4. From the Tools menu select Pre-log Function. Select Preset function, General, Multiply by a constant. Follow the wizard that starts, give the data set that will be produced a name of Wind speed and units as m/s. Enter the circumference value for your anemometer as the number to multiply by and Finish. 5. When you are ready to start logging click on Start, as the device rotates the software will convert the rotations into the wind speed for your device. Note: You can save your conversion into a setup (click on File and select Save Setup). When you come back to the software select Open Setup, find your setup file and load it. You can then log the response from your wind speed device and it will give the wind speed. Analysis of results The Count/Tachometer adaptor contains a range for the Data Harvest Anemometer that produces wind speed directly. For your home made anemometers, you will need to know the: 1. Distance from shaft to centre of the cup. 2. The calculated circumference of the device one rotation will then be known to equal a distance covered. 3. Rotations per s used with circumference to calculate the distance travelled per. It is best to complete calculations in metres and s. You will need to find: 1. Is the device reliable over a range of wind speeds? 2. Is the information presented to the competitor in meaningful way? 3. How does the position of the device affect readings? Use the information from your results to improve the design. You want to create a device that is: 1. Reliable 2. Accurate across a range of wind speeds 3. Is repeatable, i.e. gives the same result every time and doesn t need special treatment to get it working

4 Background For many events, but surprisingly not every event, there are conditions to be met to make the result legal. The legality of the result is required if records are to be created - in a 100 metre race first past the post wins regardless of wind speed. If the speed recorded is to be considered for a record the wind speed must be below 2 m/s (about 4.5 mph). In most cases the conditions and regulations are about fairness and removing possible dispute in the final result, especially in competitions where competitors take turns and don t (as in running race) compete against each other directly. The International Amateur Athletic Federation (IAAF) regulations disallow sprint and jump performances when the measured wind speed exceeds 2.0 metres per. The rule is only applied consistently to the 100 metre sprint. Problems of collecting reliable wind speed data from around the whole stadium are cited as the reason for non application on 200 and 400 metre races. It is surprising that the judges cannot place a or third wind gauge in the stadium; it is not the most complex of technologies. Air pressure and altitude also have an effect. The Mexico Olympics were noted for the number of records created, most of which stood for decades. Unlike their wind aided counterparts, performance at altitude does qualify for record status. More recently attention has been turned to the equipment used in sport; in 2009 FINA (the regulatory body for swimming competitions) changed rules to limit the effect of friction reducing swimwear. In the late 1990 s rules were changed about the basic construction of javelins. Throwing technique had so improved that javelins were flying through the air and landing flat to the field, this was making the determination of distance extremely difficult. By moving the centre of gravity of the javelin it made the javelin always fall point first to the ground. The result for the athletes was a 10 m drop in distance. To work around this manufacturers altered the finish on the javelin to lift the point higher in flight. These modifications have also been regulated away. Football has strict regulations about the ball size, pressure, pattern, etc., as does golf and tennis. Winning is not just about the athletes performance, it also about winning fairly compared to any other competitor. The increasing reliance on technology to enhance performance has made some wonder why we worry about performance enhancing drugs in sport. They argue that both add a degree of unfairness, if one is wrong then they both are wrong, alternatively if one is acceptable then both are. Table 1: Converting to METRES PER SECOND Mph / Rounding has been used in presenting the metres per value

5 Table 2: Converting to MILES per HOUR x Rounding has been used in presenting the miles per value