Answer:
When the velocity doesn't change its direction
Explanation:
Since velocity vector has 2 components: direction and magnitude, and speed is the velocity's magnitude. So if the velocity doesn't change its direction, we essentially use its magnitude, aka speed, to calculate the rate of change for acceleration.
Yes!
I think there are two ways you could go with this answer:
1) Acceleration is the change in velocity over time, it can be negative or positive. If you have an object that is already moving forwards in a straight line and give it a constant negative acceleration, it will slow down and then start going in reverse.
2)Velocity is a vector, meaning it has both magnitude and direction. In the example above, the acceleration is due to a change in magnitude, or speed (from +ve to -ve) but not a change in direction. Something that has constant speed but is changing direction is also accelerating (like something that is orbiting). You could use the earth as an example, which is constantly accelerating due to moving in a circle around the sun. At any time in the year you can say that in half a year's time the earth's direction will be reversed.
1 - Vibrate east and west
Sound waves are <em>longitudinal waves</em>, that means the vibrations are parallel to the direction of energy transfer. If the energy transfer is going East, then the vibrations will be East and West creating compressions and rarefactions in the air.
