Building your own world

What the Activity is for

A modelling package is used to create a world with which students interact. Adding rules to this world corresponds to making empirical discoveries made in the lived-in world. You can exploit this to make explicit aspects of how physics works, including unpacking the idea of a law of nature – here a constraint on the values of interacting quantities.

What to Prepare

• a modelling program (A sample model is provided, or choose your own tool)
• a means of projecting the screen to share it with the class

What Happens During this Activity

First build a simple imagined world, where there are three quantities: force, mass and acceleration. Add sliders to control these variables. You might also like to add an x–y scatter graph to plot a pair of these variables, and perhaps other representations as you choose. Set the model running, and use the sliders to vary the quantities. Notice that there is no connection between the variables: no pattern on the graph. This does not mimic the world we live in.

Now add the relationship: acceleration = forcemass

Start the model running again. Suddenly you can't have any combinations of values of variables that you like – the quantities are constrained. There is a rule in the world. Here, you've inserted that rule – in history Newton found the rule. It's Newton's second law.

Here is a simplified model that you can use:

InsertCMR{FmImaginedWordlRulesSupportCMRS}

Another approach is to start with the physical, using sensors to measure the force and acceleration on an object, whilst representing those quantities on a large screen. We'd suggest measuring them independently first, then both at once. Again you'll see that the force and acceleration are constrained (a live plot of force against acceleration is a good way to show this). You'll need some quite sophisticated equipment for this, and will need to practise.

The two approaches both produce live plots of force against acceleration: one from the model and one from the experiment. That these behave in the same way, exhibiting the same behaviour, is a really good opportunity to explore the idea of functional mimicry as an aim of modelling in physics.