Answer: Wood: Medium ; Plastic: Slow
Explanation: sound will travel at a slower rate in the denser object. If sound waves of the same energy were passed through a block of wood and a block of steel, which is more dense than the wood, the molecules of the steel would vibrate at a slower rate. Thus, sound passes more quickly through the wood, which is less dense.
Sound waves are made up of kinetic energy. It takes more energy to make large molecules vibrate than it does to make smaller molecules vibrate. Thus, sound will travel at a slower rate in the more dense object if they have the same elastic properties.
