How do you determine the direction of the acceleration?

 

To state the obvious, horizontal position is plotted on the horizontal axis of a y vs x graph and vertical position is plotted on the vertical axis.� This is no different than what would be �plotted� if it were possible to take a photograph of a moving object�s path or trajectory.�

 

Notice that the y vs x graph for the current problem is a straight line.� There are four possible ways this can happen.� The diagrams below illustrate three of the four ways.� All three examples involve a ball�s motion near the earth, because the freefall acceleration from the earth is constant just as the acceleration is constant for the motions in this simulation.� Notice that in all three examples, the distance between the data points increases as the ball falls.� In each picture, the initial location of the ball is illustrated by the black data point.�

 

 

The ball�s path or trajectory is straight in all three cases because the initial velocity is either zero or has a direction that is either that same or opposite to the acceleration.� In all three cases, however, the direction of the acceleration is the same as the direction in which the ball is speeding up.�

 

Likely, a straight-line y vs x graph in this simulation will not be vertical.� Still, however, the direction of the acceleration for such a graph will be in along that straight line and in the same direction the object is speeding up.�

 

The fourth way in which a y vs x graph might be straight is if the acceleration is zero but the initial velocity is not. �Such straight lines are easy to distinguish from the examples illustrated above because the data points will be uniformly spaced.� Uniformly spaced straight line data points do indeed correspond to zero acceleration because the velocity is not changing either in magnitude or in direction.�