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Distance Time Graphs

- Understanding and interpreting

Distance Time Graphs

- Describing a journey made by an object is very

boring 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.

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.

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.

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.

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!

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.

- 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.

- 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!

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

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