Making and keeping differences

Making and keeping differences

To bring a pan of potatoes to the boil, set the hob to a high power. To keep them boiling for twenty minutes until they’re cooked, you can set the hob to a lower power. You can't just turn the hob off – the potatoes will stop boiling.

This is a common pattern around the house: you need a high power to make a change, but a lower power to maintain that change.

Examples of creating a change:

Examples of keeping a change:

It's not true of all changes: once you’ve lifted something onto a shelf or upstairs, that change stays all by itself. You don’t need to help the change stay (Unless there is some big jiggling about, like an earthquake).

Two kinds of actions with different kinds of costs

Examples of creating and maintaining differences;

Both changing and keeping a change in temperature — heating or cooling result in:

For example:

Just changing temperature results in a fixed cost only. For example bringing a kettle of water to the temperature where it boils.

Just changing the height results in a fixed cost only. For example, lifting a bag onto a shelf

Measurable changes that stay changed, needing no help

Measurable changes that need help to stay changed