# Acceleration for Position-time graphs

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## Main Question or Discussion Point

1. http://www.physicsclassroom.com/Class/1DKin/U1L3a16.gif
2. http://www.physicsclassroom.com/Class/1DKin/U1L3a17.GIF

In the first graph, I get that that the slope is negative and that the object is speeding up
And in the second graph, the slope is negative and the object is slowing down
But i'm unable to understand why the first graph has negative acceleration while the second one has positive acceleration?

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berkeman
Mentor
1. http://www.physicsclassroom.com/Class/1DKin/U1L3a16.gif
2. http://www.physicsclassroom.com/Class/1DKin/U1L3a17.GIF

In the first graph, I get that that the slope is negative and that the object is speeding up
And in the second graph, the slope is negative and the object is slowing down
But i'm unable to understand why the first graph has negative acceleration while the second one has positive acceleration?
Acceleration is the second derivative of the position versus time... mathman
1. http://www.physicsclassroom.com/Class/1DKin/U1L3a16.gif
2. http://www.physicsclassroom.com/Class/1DKin/U1L3a17.GIF

In the first graph, I get that that the slope is negative and that the object is speeding up
And in the second graph, the slope is negative and the object is slowing down
But i'm unable to understand why the first graph has negative acceleration while the second one has positive acceleration?
In the first graph, the slope is getting steeper, speed up.
In the second graph, slope is getting less steep, slowing down.

Acceleration is the second derivative of the position versus time... @berkeman Im sorry i dont understand how that relates to negative acceleration for the first and positive acceleration for the second In the first graph, the slope is getting steeper, speed up.
In the second graph, slope is getting less steep, slowing down.
@mathman that is exactly what i mentioned above...

ZapperZ
Staff Emeritus
@berkeman Im sorry i dont understand how that relates to negative acceleration for the first and positive acceleration for the second 