Purpose

To use the Doppler Effect to determine the speed of a car traveling down the highway.

Background

We have all experienced the Doppler Effect, that change in pitch of a sound as fast moving object goes past us. The observed frequency of sound can be directly related to the source frequency by this equation:

fobs=vvvsourcefsource

f_obs= observed frequency

v = speed of the wave (in this case sound 340 m/s)

v_source = the speed of the source of the sound

f_source = the frequency of the source of the sound

= use (+) if the source is moving away and (-) if the source is approaching.

The frequency of a sound can be measured using a tuner app such as theAndroid App https://play.google.com/store/apps/details?id=org.cohortor.gstrings&hl=en&pli=1 or theApple App https://apps.apple.com/us/app/n-track-tuner/id409786458. Because there may be a mixture of noises, the tuner may have a hard time settling on one frequency. You may need to write down multiple values and decide which ones make the most sense for the situation.

Pre Lab Questions

1. What change in pitch occurs due to the Doppler Effect?

2. Explain why the Doppler Effect occurs.

Experimental

For this lab you can either use the Doppler Effect Video https://www.youtube.com/watch?v=zF1g1vQvKzU provided or go out and set up your own situation to gather data from.The car in the video is going at 70 km/h, 50 km/h, or 30 km/h. Depending on which scenario you use, this value should be used to calculate your percent error.

Explain how you will gather the needed data to solve the equation above for the speed of the object.

Data and Calculations

Include all data here, clearly labeled. Show your work for calculating the speed of the car.

Post Lab Questions

1. Show the calculation for the percent error of the velocity in this lab.

2. Address your error, does it seem reasonable given the equipment you had to work with? What could be done to improve on this error?