• KellyOsbourne
In summary, the definition of distance is the amount of ground covered, and displacement is the distance in a particular direction. On a distance-time graph, the gradient represents speed, which is always non-negative. However, on a position-time graph, the gradient represents velocity, which can be negative. The negative gradient shown on the graph in the conversation is incorrect, as it would indicate a negative speed, which is impossible. It is important to distinguish between distance-time and position-time graphs to correctly interpret the data.
KellyOsbourne
I was told by my teacher that the definition for distance is just "the amount of ground covered", and that displacement is "the distance in a particular direction". I was looking at some distance-time graphs online and I saw that towards the later stage of the journey in some of the graphs, the gradient of the distance-time graph was negative. Their explanation for the negative gradient was that the object was moving towards the starting position. I do not understand that. Even if the object is moving towards the starting position, it is still covering "ground" and it would go up, right? And the gradient of a distance-time graph is the speed, and I didn't think there was anything called negative speed. I know about negative velocity, but negative speed? Please clear this for me! I want to know how the gradient of a distance-time graph can be negative, when distance is just the "ground" covered.

This could be a very stupid question :$But I am sometimes very blind to the obvious. Please help! :) Thank you a lot in advance! KellyOsbourne said: I was told by my teacher that the definition for distance is just "the amount of ground covered", and that displacement is "the distance in a particular direction". I was looking at some distance-time graphs online and I saw that towards the later stage of the journey in some of the graphs, the gradient of the distance-time graph was negative. Their explanation for the negative gradient was that the object was moving towards the starting position. I do not understand that. Even if the object is moving towards the starting position, it is still covering "ground" and it would go up, right? And the gradient of a distance-time graph is the speed, and I didn't think there was anything called negative speed. I know about negative velocity, but negative speed? Please clear this for me! I want to know how the gradient of a distance-time graph can be negative, when distance is just the "ground" covered. This could be a very stupid question :$ But I am sometimes very blind to the obvious. Please help! :)

Thank you a lot in advance!
Welcome to Physics Forums.

I distance-time graph cannot have a negative gradient, since as you say distance (and hence speed) is a scalar quantity. However, a position/displacement time graph can have a negative gradient since position/displacement is a vector quantity.

On a distance-time graph the gradient represents the speed, which is always non-negative. However, on a position-time graph, the gradient represents the velocity, which can be negative.

Could you provide a link to the graphs with the negative gradient, I have a sneaking suspicion that they are position-time graphs.

Hootenanny said:
Welcome to Physics Forums.

I distance-time graph cannot have a negative gradient, since as you say distance (and hence speed) is a scalar quantity. However, a position/displacement time graph can have a negative gradient since position/displacement is a vector quantity.

On a distance-time graph the gradient represents the speed, which is always non-negative. However, on a position-time graph, the gradient represents the velocity, which can be negative.

Could you provide a link to the graphs with the negative gradient, I have a sneaking suspicion that they are position-time graphs.

Thank you so much! Yes, that's what I thought :)
http://www.golfranger.co.uk/speed.html

Please tell me if I made a mistake in interpreting whether it was a distance-time graph or a displacement-time graph, and how I can distinguish between the two.
Again, thanks so much :)

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KellyOsbourne said:
Thank you so much! Yes, that's what I thought :)
http://www.golfranger.co.uk/speed.html

Please tell me if I made a mistake in interpreting whether it was a distance-time graph or a displacement-time graph, and how I can distinguish between the two.
Again, thanks so much :)
The graph shown on that page is clearly incorrect. The negative gradient of the red curve indicates a negative speed, which is impossible.

Is your school hosting this website?

Last edited by a moderator:
Hootenanny said:
The graph shown on that page is clearly incorrect. The negative gradient of the red curve indicates a negative speed, which is impossible.

Is your school hosting this website?

Thank you, I thought I was going bonkers!
Umm, no, my school's not hosting it. I just ran across it when I was looking for information to prepare a poster for school.

What is a distance-time graph?

A distance-time graph is a visual representation of the relationship between distance and time for a moving object. The horizontal axis represents time, while the vertical axis represents distance. The slope of the graph indicates the speed of the object.

What does a negative gradient on a distance-time graph mean?

A negative gradient on a distance-time graph means that the object is moving in the opposite direction of the positive direction on the distance axis. This indicates that the object is moving towards the starting point or in the negative direction.

How is the speed of an object determined from a distance-time graph?

The speed of an object can be determined from a distance-time graph by calculating the slope of the line. The slope is equal to the change in distance divided by the change in time. This will give the average speed of the object between the two points on the graph.

What is the difference between a negative gradient and a positive gradient on a distance-time graph?

A negative gradient on a distance-time graph indicates that the object is moving in the opposite direction of the positive direction on the distance axis, while a positive gradient indicates that the object is moving in the same direction as the positive direction on the distance axis. A positive gradient also indicates that the object is moving away from the starting point.

How can a distance-time graph be used to predict the motion of an object?

A distance-time graph can be used to predict the motion of an object by extrapolating the line on the graph. By extending the line, you can determine where the object will be at a certain time in the future or in the past. This can help in predicting the future position or speed of the object.

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