Physics Unit 9 (Part 2)

We learned more about waves and sound in class on Friday. The picture above is an illustration of the range of human hearing (please excuse my bad drawing). As you can see in the picture, humans can hear sonic frequencies, which are between 20 Hz and 20,000 Hz. Animals such as whales and fish can hear infrasonic frequencies, which are from 20 Hz and down. On the other hand, elephants, bats, and dogs are a few animals that can hear ultrasonic frequencies of 20,000 Hz and more. (all of my information about animals came from the internet...)

Through a lab that involved tuning forks (I keep calling them pitch forks in my head, it's a problem), a graduated cylinder almost completely filled with water, and a tube of some sort. The purpose of the lab was to learn how to find the speeds of waves. First, we would hit the tuning fork on something harder so it would vibrate and create a pitch due to its natural frequency. Once the tuning fork is creating a sound, we would put it over the tube, which was submerged in the water, and then lift it slowly until the sound of the tuning fork was made by the rest of the graduated cylinder. When that happened, we were able to find the wavelengths of the tuning fork was making, by measuring the length of the tube from where it came out of the water to the bottom of the tuning fork, then multiplying that by four. Once we found the wavelengths, we were able to find the wave speed by multiplying the wavelengths by the frequencies of the tuning forks.

In class we also learned more vocab words, such as:
Refraction = the bending of waves due to changes in the medium
Reflection = the bouncing of waves
Dispersion = the spreading out of waves
Standing waves = waves that look like they're not moving
Natural frequency = the frequency of an object wants to vibrate at after an external disturbance
Resonance = the increase in amplitude of a system exposed to a force at an object's natural frequency
Sound = a vibration that causes a longitudinal wave
Pitch = the frequency of sound
Speed of sound in air = 331 + .6(Tc)

• 331 = the speed of sound in dry air at 0°C
• Tc = temperature in celcius