Distance Time Graphs Understanding and interpreting Distance vs

Distance Time Graphs Understanding and interpreting

Distance vs. Time Graphs • In science, graphs are often used to communicate information. Plotting distance versus time can tell you a lot about a journey. Let's look at the axes: y x • Time always runs horizontally (x-axis). The arrow shows the direction of time. The further to the right, the longer time from the start. • Distance runs vertically (y-axis). The higher up the graph we go, the further we are from the start.

What does an object look like on a d vs. t graph when it’s not moving ? • If something is not moving, a horizontal line is drawn on a distance-time graph (dt-graph). • Time is increasing to the right, but its distance does not change. It is stationary.

Moving at a constant speed… • If something is moving at a constant speed, it means we expect the same increase in distance in a given time: • Time is increasing to the right, and distance is increasing steadily with time. It moves at a steady speed.

Can you describe what is going on here? • For the first part of the journey shown by the graph below, the object moved at a constant (but relatively slow) speed. • It then suddenly increased its speed, covering a much larger distance in the same time.

What is the effect of line ‘Steepness’, (a. k. a. slope)… • Both lines below show that each object moved the same distance, but the steeper yellow line got there in less time • A steeper gradient indicates a larger distance moved in a given time. In other words, greater speed. • Both lines are of constant gradient (slope), so both speeds are constant.

Change in speed (a. k. a. acceleration) • The line below is showing an increase in speed as time passes since the gradient (slope) is getting steeper (i. e. curving upwards). • In other words, in a given period of time, the distance the object moves is larger – i. e. it is accelerating.

Multiple Speed Events There are three parts to the journey shown below: • (1) Moving at a constant speed (2) Not moving for quite some time (3) Moving again, but at high constant speed

Finding speed from d vs. t graphs • We can see that the motion shown by the yellow line is fastest. • By definition, average speed = change in distance / change in time so the slope of the line will give us the speed! • Yellow: speed = D d = 30. m – 0 m = 30. m = 3. 0 m/s D t 10. s – 0 s 10. s • Blue: speed = D d = 20. m – 0 m = 20. m = 1. 0 m/s D t 20. s – 0 s 20. s