183_notes:graphing_motion

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183_notes:graphing_motion [2021/09/06 13:51] – dmcpadden183_notes:graphing_motion [2025/11/12 21:20] (current) – hallstein
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 $$\vec{r}_f=\vec{r}_i + \vec{v}_{avg} \Delta t$$ $$\vec{r}_f=\vec{r}_i + \vec{v}_{avg} \Delta t$$
  
-While the motion of the car, in principle, can occur 3 dimensions, it's not possible to represent all three dimensions and the time variable on a single 2-D graph. So, we have to select a component of the car's position (or velocity) to plot. In this case, let's assume the car moves to the right (i.e., in the +x direction). Perhaps, the plot of the car's position vs time looks like this:+While the motion of the car, in principle, can occur 3 dimensions, it's not possible to represent all three dimensions and the time variable on a single 2-D graph. So, we have to select a component of the car's position (or velocity) to plot. In this case, let's assume the car moves to the right (i.e., in the +x direction). Perhaps, the plot of the car's position vs time looks like the plot linked here: [[https://msuperl.org/interactive/mechanics/CV_position_vs_time.html|Constant velocity position vs. time]] 
 +/* 
 +{{url>https://chart-studio.plotly.com/~PERLatMSU/10/graph-of-x-position-vs-time-for-a-car-moving-with-constant-velocity/#plot 640px,480px}} 
 +*/
  
- 
- 
-{{url>https://chart-studio.plotly.com/~PERLatMSU/10/graph-of-x-position-vs-time-for-a-car-moving-with-constant-velocity/#plot 640px,480px}} 
  
 Here, you can see that the position of the car changes linearly with time, as we would predict for a car moving at constant velocity. From this graph, you can also determine the car's initial position (12 m), final position (132 m), and average velocity (12 m/s). Here, you can see that the position of the car changes linearly with time, as we would predict for a car moving at constant velocity. From this graph, you can also determine the car's initial position (12 m), final position (132 m), and average velocity (12 m/s).
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 $$v_{x} = \mathrm{instantaneous\:slope} = \dfrac{dx}{dt}$$ $$v_{x} = \mathrm{instantaneous\:slope} = \dfrac{dx}{dt}$$
  
-For position versus time graphs where the position does not change linearly, you might need to determine (by taking the derivative) or approximate (by measuring very close points) the instantaneous velocity to model or explain the motion. For example in the graph below, a car moves to the right under [[:183_notes:constantf|constant force]]. Here, the slope (and thus, the velocity) changes at a constant rate and the average and instantaneous velocities are not the same.+For position versus time graphs where the position does not change linearly, you might need to determine (by taking the derivative) or approximate (by measuring very close points) the instantaneous velocity to model or explain the motion. For example in the graph linked here: [[https://msuperl.org/interactive/mechanics/CA_position_vs_time.html|Constant force position vs. time]], a car moves to the right under [[:183_notes:constantf|constant force]]. Here, the slope (and thus, the velocity) changes at a constant rate and the average and instantaneous velocities are not the same.
  
-{{url>https://chart-studio.plotly.com/~PERLatMSU/15.embed 640px,480px}}+/*{{url>https://chart-studio.plotly.com/~PERLatMSU/15.embed 640px,480px}}*/
  
  
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 \\ \\
  
-Sometimes, you will want to graph the velocity of the object as a function of time. Again, you have to graph a single component at a time. So, let's go back to the example of a car moving with constant velocity. In that case, we'd expect the velocity vs time graph to be a flat line taking on the value of the slope. In the graph below, we find that is the case.+Sometimes, you will want to graph the velocity of the object as a function of time. Again, you have to graph a single component at a time. So, let's go back to the example of a car moving with constant velocity. In that case, we'd expect the velocity vs time graph to be a flat, horizontal line taking on the value of the slope. In the graph linked here [[https://msuperl.org/interactive/mechanics/CV_velocity_vs_time.html|Constant velocity, velocity vs. time]], we find that is the case. 
 + 
 +/*{{url>https://chart-studio.plotly.com/~PERLatMSU/15.embed 640px,480px}}*/
  
-{{url>https://chart-studio.plotly.com/~PERLatMSU/15.embed 640px,480px | Constant Velocity (velocity vs time)}}+/*{{url>https://chart-studio.plotly.com/~PERLatMSU/15.embed 640px,480px | Constant Velocity (velocity vs time)}}*/
  
 In addition, we can use the position update formula to show that the x-displacement ($\Delta x$) is the area under this curve: In addition, we can use the position update formula to show that the x-displacement ($\Delta x$) is the area under this curve:
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 This is precisely how one defines a [[http://en.wikipedia.org/wiki/Riemann_sum|Riemann sum]] to determine the area under a function. This area is highlighted in light blue, and is precisely equal to the difference in the initial and final position in the first graph (120 m). The car travels at 12 m/s for 10 s. Notice the displacement is positive because the area under the curve is measured from the function to y=0. This is precisely how one defines a [[http://en.wikipedia.org/wiki/Riemann_sum|Riemann sum]] to determine the area under a function. This area is highlighted in light blue, and is precisely equal to the difference in the initial and final position in the first graph (120 m). The car travels at 12 m/s for 10 s. Notice the displacement is positive because the area under the curve is measured from the function to y=0.
  
-For situations where the object does no move with constant velocity, the area under the velocity vs time graph is still the displacement, it just might be slightly more complicated to calculate. For example, here's the velocity vs time graph for when the car moves under a [[:183_notes:constantf|constant force]].  +For situations where the object does no move with constant velocity, the area under the velocity vs time graph is still the displacement, it just might be slightly more complicated to calculate. For example, the graph link here: [[https://msuperl.org/interactive/mechanics/CA_velocity_vs_time_area_fill.html|Constant force, velocity vs. time]]  is the velocity vs time graph for when the car moves under a [[:183_notes:constantf|constant force]].  
  
-{{url>https://plot.ly/~PERLatMSU/16/640/480 640px,480px | Constant force (velocity vs time)}}+/*{{url>https://plot.ly/~PERLatMSU/16/640/480 640px,480px | Constant force (velocity vs time)}}*/
  
 The triangular area (highlighted in light blue) under the curve is the displacement of the car in the x-direction. Notice it's positive because it's above the y-axis. "Area under the curve" actually refers the the area between the function and y=0. If the plot is below the y=0, then that part of the area is negative. The triangular area (highlighted in light blue) under the curve is the displacement of the car in the x-direction. Notice it's positive because it's above the y-axis. "Area under the curve" actually refers the the area between the function and y=0. If the plot is below the y=0, then that part of the area is negative.
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