(D-T Graphs, sometimes called P-T or Position-Time Graphs) Distance-Time Graphs (D-T Graphs, sometimes called P-T or Position-Time Graphs)
The Meaning of Shape for a d-t Graph We can use distance vs. time graphs to describe motion. The motion of an object is reflected in the shape and the slope of the lines on a distance vs. time graph.
A car moving right… To begin, consider a car moving with a constant, rightward (+) velocity - of +10 m/s.
Distance-time graph This is the distance-time graph for this car. Note that a motion described as a constant, positive velocity results in a line of constant and positive slope when plotted as a position-time graph.
Distance-time graph Now consider a car moving with a rightward (+), changing velocity - that is, a car that is moving to the right but speeding up or accelerating.
Distance-time graph The resulting graph would look like this. Note that a motion described as a changing, positive velocity results in a line of changing and positive slope when plotted as a position-time graph.
The Importance of Slope Rightward direction Positive Velocity Changing Velocity (acceleration) Rightward direction Positive Velocity Constant Velocity
The Importance of Slope Slower velocity/speed Faster velocity/speed The faster the speed, the steeper the slope.
Leftward Velocity Slow, Leftward(-) Fast, Leftward(-) Constant Velocity Constant Velocity
Leftward velocity Leftward(-) Velocity Slow to Fast Leftward (-) Velocity Fast to Slow
ZERO slope on a D-T graph means the car is STOPPED Think – the distance doesn’t change as time goes by. This means the car is standing still.
In Summary: The shape of the line on the graph (straight, curving, steeply sloped, mildly sloped, etc.) is descriptive of the object's motion. A zero slope means the car is stopped A shallow slope means a slow speed; A steep slope means a fast speed; A positive slope means going in a certain direction; A negative slope means going in the opposite direction; A constant slope (straight line) means a constant speed; A changing slope (curved line) means a changing speed (acceleration).