Difference between revisions of "Measure Speed"
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#Start the runner and your watch at the same time. To sync up the timing as best as possible, yell “Go!” and start the watch at the same time. If you realize that the timing was off, have the runner reset and try again. | #Start the runner and your watch at the same time. To sync up the timing as best as possible, yell “Go!” and start the watch at the same time. If you realize that the timing was off, have the runner reset and try again. | ||
#Stop your watch when the runner crosses the finish line. Watch closely to see when the runner crosses the point designated as the finish line. Be sure to stop the watch as close to the exact moment he crosses as possible. | #Stop your watch when the runner crosses the finish line. Watch closely to see when the runner crosses the point designated as the finish line. Be sure to stop the watch as close to the exact moment he crosses as possible. | ||
| − | #Divide the distance the runner traveled by the number of seconds elapsed. This division is the calculation to determine the runner’s speed. The equation for speed is distance traveled/time to travel that distance.<ref>http://study.com/academy/lesson/calculating-average-speed-formula-practice-problems.html</ref> Using the example length of 100 m (328 ft), if the runner took 10 seconds to run that distance, the runner's speed would be 100 m (328 ft) divided by 10, or 10 m/sec (32.8 feet per second). | + | #Divide the distance the runner traveled by the number of seconds elapsed. This division is the calculation to determine the runner’s speed. The equation for speed is distance traveled/time to travel that distance.<ref name="rf1">http://study.com/academy/lesson/calculating-average-speed-formula-practice-problems.html</ref> Using the example length of 100 m (328 ft), if the runner took 10 seconds to run that distance, the runner's speed would be 100 m (328 ft) divided by 10, or 10 m/sec (32.8 feet per second). |
#* Multiplying 10 m/sec by 3,600 (the number of seconds in an hour), the runner traveled 36,000 meters per hour, or 36 kilometers per hour (1 kilometer equals 1,000 m). | #* Multiplying 10 m/sec by 3,600 (the number of seconds in an hour), the runner traveled 36,000 meters per hour, or 36 kilometers per hour (1 kilometer equals 1,000 m). | ||
#* Multiplying 32.8 feet per second by 3,600, the runner traveled 118,080 feet per hour, or 22.4 miles per hour (5,280 feet equals 1 mile). | #* Multiplying 32.8 feet per second by 3,600, the runner traveled 118,080 feet per hour, or 22.4 miles per hour (5,280 feet equals 1 mile). | ||
=== Measuring the Speed of Sound === | === Measuring the Speed of Sound === | ||
| − | #Find a wall that reflects sound. A large brick or concrete wall will work well for this experiment. You can test the wall by clapping your hands or yelling and listening for an echo. If you hear a strong echo, it’s a good wall to use.<ref> http://www.nuffieldfoundation.org/practical-physics/measuring-speed-sound-using-echoes</ref> | + | #Find a wall that reflects sound. A large brick or concrete wall will work well for this experiment. You can test the wall by clapping your hands or yelling and listening for an echo. If you hear a strong echo, it’s a good wall to use.<ref name="rf2"> http://www.nuffieldfoundation.org/practical-physics/measuring-speed-sound-using-echoes</ref> |
#Measure a distance of at least 50 m (54.5 yards) from the wall. A 50 m (54.5 yd) distance is suggested because it should give you enough time to make accurate measurements. Because you are taking into account the distance the sound will travel from you to the wall and back to you, you are actually measuring a distance of 100 m (109 yd). | #Measure a distance of at least 50 m (54.5 yards) from the wall. A 50 m (54.5 yd) distance is suggested because it should give you enough time to make accurate measurements. Because you are taking into account the distance the sound will travel from you to the wall and back to you, you are actually measuring a distance of 100 m (109 yd). | ||
#* Measure the distance with a tape measure. Try to be as accurate as possible with your measurements. | #* Measure the distance with a tape measure. Try to be as accurate as possible with your measurements. | ||
| − | #Clap your hands in time to the echo from the wall. Stand in front of the wall at the measured distance and clap your hands slowly. You should be able to hear the echo as you do it. Speed up or slow down your clapping rhythm until your clap coincides with the echo from the previous clap.<ref>http://www.nuffieldfoundation.org/practical-physics/measuring-speed-sound-using-echoes</ref> | + | #Clap your hands in time to the echo from the wall. Stand in front of the wall at the measured distance and clap your hands slowly. You should be able to hear the echo as you do it. Speed up or slow down your clapping rhythm until your clap coincides with the echo from the previous clap.<ref name="rf3">http://www.nuffieldfoundation.org/practical-physics/measuring-speed-sound-using-echoes</ref> |
#* If you are perfectly in sync, you should not hear the echo, but only your clap. | #* If you are perfectly in sync, you should not hear the echo, but only your clap. | ||
| − | #Clap your hands 11 times while recording time with the stopwatch. Have your friend start the watch on the first clap and stop on the last clap. By clapping 11 times you will have timed 10 distance intervals for the sound of the clap to reverberate off the wall. In essence, the sound has traveled 10 times the initial 100 m distance.<ref> http://www.instructables.com/id/How-to-measure-the-speed-of-sound-with-two-lumps-o/</ref> | + | #Clap your hands 11 times while recording time with the stopwatch. Have your friend start the watch on the first clap and stop on the last clap. By clapping 11 times you will have timed 10 distance intervals for the sound of the clap to reverberate off the wall. In essence, the sound has traveled 10 times the initial 100 m distance.<ref name="rf4"> http://www.instructables.com/id/How-to-measure-the-speed-of-sound-with-two-lumps-o/</ref> |
#* Clapping 11 times also gives your friend enough time to start and stop the watch accurately. | #* Clapping 11 times also gives your friend enough time to start and stop the watch accurately. | ||
#* Perform this step multiple times and average the times together to get a more accurate measurement. To average the trials, add up all the times and divide by the number of trials. | #* Perform this step multiple times and average the times together to get a more accurate measurement. To average the trials, add up all the times and divide by the number of trials. | ||
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#Divide the distance the sound traveled by the amount of time it took to clap. This will measure the speed of the sound of the clap from your hands to the wall and back to your ears. | #Divide the distance the sound traveled by the amount of time it took to clap. This will measure the speed of the sound of the clap from your hands to the wall and back to your ears. | ||
#* For example, let’s say it took 2.89 seconds for the 11 claps. To find speed we take the distance, 1000 meters, and divide by the time, 2.89 seconds to get a speed of sound of 346 m/sec. | #* For example, let’s say it took 2.89 seconds for the 11 claps. To find speed we take the distance, 1000 meters, and divide by the time, 2.89 seconds to get a speed of sound of 346 m/sec. | ||
| − | #* The speed of sound at sea level is 340.29 m/sec (1,116 feet per second or 761.2 mph).<ref>http://www.fighter-planes.com/jetmach1.htm</ref> Your calculations should come close to this figure, but may not match it exactly, especially if you aren’t at sea level. At higher altitudes, the air gets thinner and the speed of sound is slower. | + | #* The speed of sound at sea level is 340.29 m/sec (1,116 feet per second or 761.2 mph).<ref name="rf5">http://www.fighter-planes.com/jetmach1.htm</ref> Your calculations should come close to this figure, but may not match it exactly, especially if you aren’t at sea level. At higher altitudes, the air gets thinner and the speed of sound is slower. |
| − | #* Sound travels faster through liquids and solids than it does through air because sounds moves more quickly through materials of higher density.<ref>http://everythingmaths.co.za/science/grade-10/10-sound/10-sound-02.cnxmlplus</ref> | + | #* Sound travels faster through liquids and solids than it does through air because sounds moves more quickly through materials of higher density.<ref name="rf6">http://everythingmaths.co.za/science/grade-10/10-sound/10-sound-02.cnxmlplus</ref> |
=== Measuring Wind Speed === | === Measuring Wind Speed === | ||
| − | #Obtain an anemometer. An anemometer is a device that measures wind speed.<ref>http://www.scientificamerican.com/article/bring-science-home-wind-speed/</ref> It consists of 3 or 4 cups mounted on wires attached to a central rotating shaft. Wind catches the cups and makes them spin. The faster the wind blows, the faster the cups spin around their axis. | + | #Obtain an anemometer. An anemometer is a device that measures wind speed.<ref name="rf7">http://www.scientificamerican.com/article/bring-science-home-wind-speed/</ref> It consists of 3 or 4 cups mounted on wires attached to a central rotating shaft. Wind catches the cups and makes them spin. The faster the wind blows, the faster the cups spin around their axis. |
#* You can either buy an [[Make an Anemometer|anemometer]] or make your own. | #* You can either buy an [[Make an Anemometer|anemometer]] or make your own. | ||
| − | #* To make your own, get five three-ounce paper cups, two straws, a sharpened pencil with an eraser, a stapler, a small sharp pin, and a ruler.<ref | + | #* To make your own, get five three-ounce paper cups, two straws, a sharpened pencil with an eraser, a stapler, a small sharp pin, and a ruler.<ref name="rf7" /> Color the sides of one of the cups to make it distinct from the others. |
#* Punch a hole in the side of four of the cups about 1 inch from the rim. In the fifth cup, punch four holes equally spaced around the cup about 1 inch from the rim. Also, punch one hole in the bottom of this cup. | #* Punch a hole in the side of four of the cups about 1 inch from the rim. In the fifth cup, punch four holes equally spaced around the cup about 1 inch from the rim. Also, punch one hole in the bottom of this cup. | ||
#* Push one straw through the side of one of the cups leaving about 1 inch of straw inside the cup. Staple the straw to the side of the cup. Feed the rest of the straw through the fifth cup with 4 holes in one side and out the other. Place a second cup on the end of this straw and staple it in place. Make sure all of the cups face the same direction. | #* Push one straw through the side of one of the cups leaving about 1 inch of straw inside the cup. Staple the straw to the side of the cup. Feed the rest of the straw through the fifth cup with 4 holes in one side and out the other. Place a second cup on the end of this straw and staple it in place. Make sure all of the cups face the same direction. | ||
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#* Multiplying 30.9 feet per second by 3,600 gives 111,240 feet per hour, divided by 5,280 gives 21.1 miles per hour. | #* Multiplying 30.9 feet per second by 3,600 gives 111,240 feet per hour, divided by 5,280 gives 21.1 miles per hour. | ||
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== Tips == | == Tips == | ||
