Iterative Prediction of Spring-Mass System: Difference between revisions

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''Step 1'': We begin by calculating the object's initial momentum and the sum of the forces acting on it.
''Step 1'': We begin by calculating the object's initial momentum and the sum of the forces acting on it.


<math>{\vec{p}_{i} = {{m}\vec{v}_{i}}</math>
<math>{\vec{p}_{i}} = {{m}*\vec{v}_{i}}</math>





Revision as of 14:27, 1 December 2015

claimed by kgiles7

Short Description of Topic

The Main Idea

A simple spring-mass system is a basic illustration of the momentum principle. The principle of conservation of momentum can be repeatedly applied to predict the system's future motion.

vertical spring-mass system

A Mathematical Model

The Momentum Principle provides a mathematical basis for the repeated calculations needed to predicts the system's future motion. The most useful form of this equation for predicting future motion is referred to as the momentum update form, and can be derived by rearranging the Momentum Principle as shown below:

[math]\displaystyle{ {{&Delta;p}_{system}} = {\vec{F}_{net}{&Delta;t}} }[/math]

[math]\displaystyle{ {\vec{p}_{f} - \vec{p}_{i} = \vec{F}_{net}{&Delta;t}} }[/math]

[math]\displaystyle{ {\vec{p}_{f} = \vec{p}_{i} + \vec{F}_{net}{&Delta;t}} }[/math]


In order to update the object's velocity and position, similar equations can be used. Together, they can be used to model the future motion of a spring-mass system.

Velocity Update Formula: [math]\displaystyle{ {\vec{v}_{f} = \vec{v}_{i} + \frac{\vec{F}_{net}}{m}}{&Delta;t} }[/math]

Position Update Formula: [math]\displaystyle{ {\vec{r}_{f} = \vec{r}_{i} + \vec{v}_{avg}{&Delta;t}} }[/math]


A Computational Model

How do we visualize or predict using this topic. Consider embedding some vpython code here Teach hands-on with GlowScript



Examples

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Simple

vertical spring-mass system

Example 1: The simplest example of a spring mass system is one that moves in only one-direction. Consider a massless spring of length 1 m with spring constant 100 N/m. If a 10 kg mass is released from rest while the spring is stretched downward to a length of 1.5 m, what is it's momentum after 0.5 seconds? The mass oscillates vertically, as shown to the right.

This problem can be solved through repeated iterations either by hand or by using a computer model such as VPython. Both methods are shown below.

Manual Solution: The time step used for each iteration must be small enough that we can assume a constant velocity over the interval, but not so large that solving the problem becomes incredibly time-consuming. An appropriately small time step here is approximately 0.1 seconds.

Step 1: We begin by calculating the object's initial momentum and the sum of the forces acting on it.

[math]\displaystyle{ {\vec{p}_{i}} = {{m}*\vec{v}_{i}} }[/math]




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