- #1
How Accurate is Your Speed-Time Graph?
- Context: High School
- Thread starter Anzas
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Discussion Overview
The discussion revolves around the accuracy and interpretation of speed-time graphs as presented in a classroom setting. Participants explore the implications of graphing speed as a function of time, particularly in relation to the underlying physics concepts of velocity, acceleration, and the nature of idealized versus realistic representations in physics education.
Discussion Character
- Debate/contested
- Conceptual clarification
- Technical explanation
Main Points Raised
- One participant presents their speed-time graph and seeks feedback on its accuracy.
- Another participant agrees with the graph's representation, noting that the distance vs. time graphs consist of straight line segments, indicating constant speed during those intervals.
- A participant critiques the teacher's terminology, arguing that speed is not defined at certain points due to infinite acceleration, suggesting a misunderstanding in the graph's presentation.
- Further discussion questions whether the teacher's graph could be interpreted as suggesting unrealistic scenarios, such as instantaneous changes in speed.
- Another participant points out that the velocity is undefined at points where the distance graph has corners, leading to jumps in speed values.
- One participant asserts that the graph represents an ideal case where velocity can change instantaneously, which they find irrational.
- A later reply emphasizes the need for teaching methods that effectively convey the intended concepts without introducing confusion through overly simplistic representations.
Areas of Agreement / Disagreement
Participants express differing views on the appropriateness of the graph and its implications for understanding speed and acceleration. There is no consensus on whether the graph is a helpful educational tool or a source of confusion.
Contextual Notes
Participants note limitations in the graph's representation, particularly regarding the definition of speed at points of infinite acceleration and the idealized nature of the graph that may not reflect real-world physics accurately.
Who May Find This Useful
This discussion may be of interest to students studying physics, educators seeking effective teaching methods for graphing concepts, and individuals interested in the nuances of speed and acceleration in physics.
- #2
HallsofIvy
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Looks good. The "distance vs time" graphs (I assume that's what they are- you didn't say so) are made of straight line segments so the corresponding speed is a constant, the slope of the distance graph and the speed vs time graph is a horizontal straight line for that time interval.
- #3
Anzas
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that teacher of my, called the speed/time graph a function, the speed is not even defined at a few points because the acceleration is infinite 
- #4
DaveC426913
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Can you elaborate? Is your prof calling it a time machine? or are you?
Unless I misunderstand, it seems that you are splitting hairs. This is a sketch, designed to show the relevant aspects of the data - the relationship between changing velocity and position. The accelerative aspects are made deliberately trivial. Technically, yes, the slope would be defined, and in reality would not be vertical.
Unless I misunderstand, it seems that you are splitting hairs. This is a sketch, designed to show the relevant aspects of the data - the relationship between changing velocity and position. The accelerative aspects are made deliberately trivial. Technically, yes, the slope would be defined, and in reality would not be vertical.
- #5
Anzas
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i just call it a time mechine as a joke (because the acceleration at a few points is infinite) i personally think its a mistake giving such a graph in class all it does is make people confused on how it is possible that the acceleration is infinite.
- #6
HallsofIvy
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The point about "the speed is not even defined at a few points because the acceleration is infinite" refers to the points at which the distance graph has "corners". The velocity itself is not defined there and the graph "jumps" from one value to another.
- #7
joyful55
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Well, let's just say that these graphs are on an ideal case where velocity is able to switch to any value at any point of time which is in fact irrational.
- #8
DaveC426913
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You are clever enough to see that the graph is too simplistic for your own level of understanding. Not everyone will grasp the concepts quite so quickly.
The question at hand is, what treatment best teaches the student body the concepts intended?
If the teacher is trying to teach the relationship between velocity and distance, an idealized graph will do that, without obfuscating the issue with real - yet contextually irrelevant - facts.
The question at hand is, what treatment best teaches the student body the concepts intended?
If the teacher is trying to teach the relationship between velocity and distance, an idealized graph will do that, without obfuscating the issue with real - yet contextually irrelevant - facts.
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