Distance Time Graphs

1
Distance Time Graphs

• Understanding and interpreting

2
Distance Time Graphs

• Describing a journey made by an object is not
  exciting if you just use words. As with much of
  science, graphs are more revealing.
• Plotting distance against time can tell you a lot
  about a journey. Let's look at the axes
• Time always runs horizontally (the x-axis). The
  arrow shows the direction of time. The further to
  the right, the longer time from the start.
• Distance runs vertically (the y-axis). The higher
  up the graph we go, the further we are from the
  start.

3
Not moving? This is what it looks like

• 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.

4
Moving.

• If something is moving at a steady 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.

5
Steady Speed

• If something is moving at a steady 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.

6
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 steady (slow)
  speed.
• It then suddenly increased its speed, covering a
  much larger distance in the same time.
• This sort of motion is not very realistic, but is
  easy to understand. It also makes calculations
  easier!

7
What is the effect of line Steepness, A.K.A
slope

• Both the lines below show that each object moved
  the same distance, but the steeper yellow line
  got there before the other one
• A steeper gradient indicates a larger distance
  moved in a given time. In other words, higher
  speed.
• Both lines are of constant gradient, so both
  speeds are constant.

8

• The line below is curving upwards. This shows an
  increase in speed, since the gradient is getting
  steeper
• In other words, in a given time, the distance the
  object moves is larger. It is accelerating.

9

• There are three parts to the journey shown below
  
• Moving at a steady speed, slowly Not moving for
  quite some time Moving again, but at higher
  speed
• In all the graphs so far, we have not seen any
  numbers - it's about time we did!

10
Finding speed from these types of graphs!

• We can see that the motion shown by the yellow
  line is fastest.
• By definition, speed distance / time so the
  steepness (or gradient) of the line will give us
  the speed!
• Yellow speed distance / time 30 m / 10 s 3
  m/s
• Blue speed distance / time 20 m / 20 s 1
  m/s

11
Calculate the speeds of different sections within
a graph

• Stage 1 speed distance / time 100 m / 10 s
  10 m/s
• Stage 2 speed distance / time 50 m / 10 s
  5 m/s
• Stage 3 speed distance / time 150 m / 20 s
  75 m/s

12
Lets look at the Textbook!P. 365 -2, 3, 5, 6