Introduction to VENSIM

Transcription

1 ICT for Innovative Science Teachers Leonardo da Vinci programme PL1- LEO Introduction to VENSIM CC 2011 ICT for IST This project has been funded with support from the European Commission under the Lifelong Learning Programme. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

2 A. VENSIM The software VENSIM from Ventana Systems, Inc. ( can be used to model dynamic systems. These systems can be very complex, having many components with involved relationships. Appropriate educational technologies have the potential to make physics concepts more accessible through visualization, modelling and multiple representations. Students can be engaged in more powerful scientific activities and they can be supported to perform investigations that would not be possible without the use of technology. The educational potential of technology products has to be reviewed based on current learning theories on existing research. Educational software supports teachers in presenting new knowledge to students and supports students in applying and extending what they have learned on a more individual basis. Highly modular and flexible software products some of them being freely available on the internet for teaching and learning physics which can be used in the classroom. They can be used in different ways: first, as presentation aids for teaching a topic to the students, then to anchor and stimulate classroom discussions and finally encourage students applying and practicing new concepts and skills an their own. Using interactive simulations teachers can quickly discuss and demonstrate the effect of varying parameters in an experiment, and then have students make conjectures about the results. Through the manipulation of parameters and the use of different types of representations in the simulation, comprehension of the relationships among concepts, variables and phenomena can be fostered in the students. At the same time, phenomena which would not be possible to experience in a classroom or laboratory can be investigated. But simulations should not be conceived as substitutes of the real laboratory experiences. Their use as a complement of experimentation can be highly effective for learning physics concepts. This module aims to give an Introduction for using VENSIM and to support the physics teacher with ideas how to use it in the classroom. As an example, the swinging pendulum will be modelled with VENSIM. Oscillations Simulations & Modelling with VENSIM - 2

3 The Software VENSIM After start running the software and selecting new New from the File menu a Model Settings popup menu appears (see figure below) First the first time it is recommended to use the default settings by clicking OK. A window, where you have to construct a diagram model with equations appears. After having considered appropriate values for final time, time step and units for time, you can come back to the model settings window by choosing model and settings from the menu bar. The title bar, which is at the top of the Vensim screen contains the name of the Vensim-File. The main toolbar is beneath the title bar and contains typical icons for Open Model, Save, Print, Cut, Copy and Paste among others. The most important icons for building a model, the sketch tools, appear towards the left, below the main tool bar and immediately above the large, currently blank Build (Sktech) Window. You will get further details about using the software VENSIM in Activity 2: Swinging Pendulum. Oscillations Simulations & Modelling with VENSIM - 3

4 B. Student Activities ACTIVITY 1. MASS ON A SPRING Learning Objectives: 1. To learn how to use the simulation Federpendel for self controlled acquiring knowledge 2. Learn to ask own questions, make predictions and finally prove them Activity method: In this activity the students will analyze the motion of a mass on a spring. They will be asked to find out, how the parameters mass, spring constant, damping factor and displacement at the beginning influence the time for one cycle of the mass. Students shall find out, what is influenced by the displacement at the beginning. Students shall evaluate the relationship between the different graphs and compare the different points to the locus of the mass on the left. The teacher has to find out what appropriate guidance for useful investigations and explorations of the students is required. Finding out the range of parameter values: Mass: From 0,125 kg to 0,5 kg Spring constant: From 100 N/m to 300 N/m Damping factor: Form 0 to 5 kg/s Performing the first virtual experiment: 1. Choose m = 0,5 kg, spring constant = 300 N/m and damping factor = Then pull the mass down and observe the box right from T = on the left bottom of the simulation window and write it down on a piece of paper. 3. Try again with different displacement of the mass at the beginning. Is there difference in the results for T? Oscillations Simulations & Modelling with VENSIM - 4

5 4. Check the box Pfeile (=arrows) and repeat the experiment. Observe the arrows near to the mass. What do they represent? 5. Choose m = 0,125 kg, spring constant = 300 N/m and damping factor = 0. How do the value for T compares to the value for T, when the mass was 0,5 kg? Can you find a relationship between mass m and period T? Oscillations Simulations & Modelling with VENSIM - 5

6 ACTIVITY 2. SWINGUNG PENDULUM Learning Objectives: 1. To learn how to create a model with VENSIM 2. Analyse the motion of the swinging pendulum Building the model in VENSIM The basic building blocks of VENSIM are: Box Variable or Stock Rate of Flow Variable or Converter Arrow or Connector A box variable or stock is a noun and represents something that accumulates. At any instant, the magnitudes of the stocks give us a snapshot of the system. 1. Click on the rectangular stock icon. Without holding down the mouse button, move the mouse towards the in the figure below assigned area of the window. While a stock is a noun in the language of VENSIM, a rate of flow is a verb. A rate is an activity that changes magnitude of stock. The rate flow icon represents a directed pipe with a valve. 2. Click on the flow icon. 3. Then click a couple of inches to the left of the stock. 4. And then, without dragging, click the stock, so that a rectangular with a cursor appears. Oscillations Simulations & Modelling with VENSIM - 6

7 5. Type its name, v, in the rectangle and press RETURN or ENTER. 6. A diagram should appear similar to the figure below with the flow beginning in a cloud. 7. Now repeat actions 1 to 5 again for the stock Velocity and the rate of flow Acceleration 8. You will get a diagram similar to the figure below. 9. Define an auxiliary / constant variable to store the length of the rope by selecting the Variable-Auxiliary / Constant icon, which has VAR and a pencil but no box. 10. Click to the left and name the converter Length. 11. A diagram should appear similar to the figure below. Oscillations Simulations & Modelling with VENSIM - 7

8 An arrow or connector transmits an input or an output. In your model the length of the rope affects the acceleration of the bob. The acceleration of the bob is also influenced by the displacement. You indicate these relationships by connecting the length converter (variable) and the displacement stock (box variable) to the flow acceleration. 12. After selecting the connector icon, click Length and then Acceleration. 13. Without selecting another tool, you can use the same tool again and connect Displacement with Acceleration in the same way as before. 14. Small circles indicate anchors that you can drag to create arches. Define Equations and initial values: You are now ready to enter equations and initial values. To begin defining an initial Displacement, click on the Equation tool, whicj is next to the last icon on the right of the sketch tools toolbar and then click the stock Displacement. Fill in the values, you find in the figure below. Oscillations Simulations & Modelling with VENSIM - 8

9 15. Continue with defining equations and values for the other variables. Oscillations Simulations & Modelling with VENSIM - 9

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11 Running the simulation: 1. To generate a simulation dataset that you can display and graph, you click the Run a simulation icon, which appears as a running man immediately to the right of the text box containing Current. 2. Now you can change the simulation setup, such as the time step or length of the simulation, or generate another data set using a different name. Graphs: The Graphs icon appears as a picture of two small graphs to the middle, left of the Build Window. 1. First click on Displacement. 2. Then after clicking the Graphs icon, a graph popup window of Displacement versus Time appears immediately (see figure below). Oscillations Simulations & Modelling with VENSIM - 11

12 3. You can define your own graphs by clicking on the upper right icon in the menu bar. Oscillations Simulations & Modelling with VENSIM - 12

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