Understanding Negative Velocity and Displacement on a Velocity-Time Graph

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SUMMARY

The discussion clarifies that the area under a velocity-time graph represents displacement, while the total area accounts for distance. It emphasizes that the integral of the graph assigns a negative value to areas below the x-axis, indicating negative velocity and displacement. Understanding these concepts requires familiarity with integration, as it differentiates between signed and unsigned areas. The conversation highlights that students unfamiliar with integration may struggle with the concept of negative areas.

PREREQUISITES
  • Understanding of velocity-time graphs
  • Basic knowledge of integration
  • Familiarity with the concepts of distance and displacement
  • Knowledge of positive and negative values in mathematical contexts
NEXT STEPS
  • Study the fundamentals of integration in calculus
  • Learn how to interpret velocity-time graphs in physics
  • Explore the relationship between area under a curve and displacement
  • Investigate the implications of negative velocity in real-world scenarios
USEFUL FOR

Students studying physics, educators teaching calculus and physics concepts, and anyone interested in understanding the mathematical interpretation of motion through velocity-time graphs.

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Homework Statement
Is area under a velocity-time graph a distance or displacement?
Relevant Equations
Velocity = rate of change of displacement with time.
I think the area required is a displacement.
 
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Depends if you mean area or signed area (integral)
 
Thanks
 
grzz said:
Homework Statement:: Is area under a velocity-time graph a distance or displacement?
Relevant Equations:: Velocity = rate of change of displacement with time.

I think the area required is a displacement.
The area under a curve is always, by definition, a positive number. If a curve crosses the ##x## axis, then the total area between the curve and ##x## axis is the sum of all the separate areas.

The integral, however, assigns a negative sign to areas below the ##x## axis. The integral may be positive or negative or zero.

In terms of physics, the integral of a velocity time graph gives the displacement. Whereas, the total area under a velocity time graph gives the total distance.
 
Hence such a question makes sense only to students who are familiar with integration. Am I correct to say this?
 
grzz said:
Hence such a question makes sense only to students who are familiar with integration. Am I correct to say this?
Not necessarily. You can take an area below the ##x## axis to be negative, without relying on integration.
 
A student who knows about integration will not ask why the area can be negative while one who does not know about integration will ask why the area below the x axis is negative. What answer can I give him then?
 
grzz said:
A student who knows about integration will not ask why the area can be negative while one who does not know about integration will ask why the area below the x axis is negative. What answer can I give him then?
If we are talking about a velocity-time graph, then velocity is negative below the time axis. And displacement is negative. That is nothing to do with integration.
 

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