If a vehicle is coming toward you at 96 km/hr (60 miles per hour) and sounds its horn that blares at 8000 Hz, what is the frequency of the sound you hear when the speed of sound is 340 m/s (1115 ft/s)? If you know the resulting frequency, you can find the speed of the source moving toward you: The Doppler frequency equation is sometimes written as: In such as case, you would be dividing by 0, which is impossible. Note that this equation does not work if the speed of the source is equal to the speed of sound. Since we use v S as the velocity of the source, using c as the velocity of sound avoids confusion. Note: Although c is usually denoted as the speed of light, it is also often used as the speed or velocity of sound. v S is the velocity of the source toward you.The equation for the observed frequency of sound when the source is traveling toward you is: ( See Traveling Faster than Sound for more information.) Observed frequency An aircraft flying at the speed of sound or greater creates a sonic boom, which is a different effect. Note that the speed of the source must be less than the speed of sound. When the source of sound is moving toward you, the pitch you hear is higher than what was emitted from the source and the wavelength is shorter than emitted. What are the equations when the source is moving at an angle to you?.What happens when the source is moving away from you?.

What are the equations when the source is moving toward you?.

Note: This is a good idea for a science project. You need to know the initial frequency, the velocity of the source and the speed of sound, as well as the angle between the source and the line-of-sight.Īlthough you can hear the difference in frequencies, you really need to use a microphone and a frequency meter, such as an oscilloscope, to determine the initial and final frequencies. The Doppler Effect equations allow you to calculate the frequency of the sound as a source moves toward you, away from you, or even at an angle with respect to the line-of-sight.

It will be either higher or lower than the emitted frequency, depending on the direction the source is moving. The Doppler Effect for sound is the change in frequency or pitch that you hear from a moving source.

Speed of sound ft s