Here is the main thing is medium. In the free boundary wave face the air medium, but in a fixed boundary wave face different medium. The change of medium effect on the change of the reflection of wave.
Particles vibrate parallel to the direction the sound travels. It's a longitudinal wave.
Answer:
An air hockey table has a very smooth and slippery surface which reduces friction by suspending the puck on cushion of air, so that this its motion is much less altered by friction, causing it to glide in a straight line at relatively constant velocity across the table.
Explanation:
1) Pushing on a car will not always change the car's mechanical energy, but it does change yours since your physically using most of your energy to push the car.
2) In order for a cars kinetic energy to increase, the car has to be in motion when it is going down a hill, because when you go down hills and objects like that; you tend to increase in kinetic energy.
