Question

Graphs of motion

Answer 1

@matt101 that area I pointed with arrows is confusing for me. In d-t it is increasing velocity, but in a negative direction, so v-t is a straight line below the o line. However, why the a-t graph is below the graph and not above the graph?

Answer 2

Look at the slope of the v-t graph during the time you indicated! It's a negative slope, meaning a negative acceleration!

This makes sense, because according to the d-t graph, the displacement is DECREASING faster and faster over time, meaning the velocity is decreasing (or increasing in the negative direction, as you've said) over time as shown in the v-t graph, meaning there is a net negative acceleration as indicated in the a-t graph!

Answer 3

I understand makes sense, so can we say that decreasing velocity in the positive direction and increasing velocity in the negative direction, have negative acceleration?

Answer 4

Correct! In both cases, the CHANGE in velocity over time is negative!

And the graph you just posted shows a constant negative acceleration! If you apply a constant negative acceleration to an initially positive speed, that speed will get smaller and smaller (more negative) until it reaches 0 (stopped), but if you continue to apply that negative acceleration, the object will begin SPEEDING UP but in the NEGATIVE direction!