A student measures how long it takes a ball to fall to the bottom of a pipe. Which of the following would MOST reduce the acceleration of the falling ball.

Sounds propagates through some kind of medium. usually it's air, but it goes just as well through solid objects like walls, windows etc. a soundwave will compress the (air)molecules in front of it, and if this increased density wave hits your ears, you register it as sound. solid objects like walls are a lot denser than air, this means that they will damp a wave, but also carry it easier.

Can you give more detail  

Fb is the magnetic force  q is the chargev is the velocity of the charge  b is the magnetic field  the equation is: f=|q|vbsin0