Sound Waves and Pressure
Investigation 2 – Lab
This Investigation is designed to:
- demonstrate to you that in a particular type of matter, every sound is characterized by a specific wavelength,
- demonstrate to you that a specific sound is characterized by a specific frequency of vibrations,
- allow you to determine the speed of sound in air, and
- allow you to demonstrate that the speed of sounds with different frequencies is the same in the same type of matter.
Student Preparation for the Investigation includes having you gather the following materials.
Note: The materials are listed in your SDR. They are also listed below for your reference.
- (1) tuning fork with a 256 Hz, 392 Hz, or 523.3 Hz frequency
- (1) meter stick
- (1) 1000 ml graduated cylinder filled with water
- (1) 50 cm length of 1 x 1 ¼” PVC pipe
- (1) calculator, one large “for experiment only” container
- (1) size 7 rubber stopper
Direct one student from each lab group to collect the materials listed in their SDRs.
- During Investigation 2 you will measure the wavelength of standing waves in air made by tuning forks of specific frequencies. You will then use this data to calculate the speed of sound in air.
- You will perform three Trials during this Investigation. Each of the Trials requires one of the three different tuning forks so that by the end of the Investigation, each student group should have collected data for each of the tuning forks.
- Reflect on the PreLab video as you move through the procedural steps.
- During the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help you keep on track, read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it).
- Complete all of the procedural steps in your SDR.
Note: The procedural steps are listed below for your reference.
- Fill the graduated cylinder up to the rim with water. Place the graduated cylinder in the larger “for experiment only” container.
- One group member should place the length of the PVC pipe into the water and push it all the way to the bottom of the cylinder. Some of the water will spill into the container.
- This member should hold the PVC pipe at the open end extending out of the water.
- Read the frequency from the side of the tuning fork and find it in Table A.
- Another group member should place the rubber stopper on the table next to the graduated cylinder with its large side down.
- This member should hold the handle of the tuning fork and forcefully strike the rubber stopper with one of the prongs. They should immediately hold the prongs of the tuning fork above the open end of the PVC pipe.
- The group member holding the PVC pipe should move it up and down, in and out of the water, until the sound made by the tuning fork suddenly becomes louder. At this point, stop pulling the PVC pipe out of the water. If the tuning fork touches the PVC pipe and its vibration stops, strike the stopper again and continue pulling the PVC pipe out of the water.
- A third group member should use the meter stick and measure the length of the PVC pipe extending out of the water from the open end to the surface of the water. Record this distance in centimeters in Table A.
- Convert the measured distance from centimeters to meters by dividing by 100. Record each distance in meters in Table A.
Note: By adjusting the length of the PVC pipe that is out of the water, you are adjusting the standing wave so that an antinode is located at the opening of the PVC pipe. This allows you to hear the sound of the tuning fork much more clearly and with a greater volume.
- Obtain another tuning fork of a second, different frequency from another group. Repeat steps 5 through 11 from Trial 1 using the second tuning fork.
- Obtain another tuning fork of a third, different frequency from another group. Repeat the steps 5 through 11 from Trial 1 using the third tuning fork.
Clean up your lab bench after you have completed your experiments.