Newton's 1st law:
|Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.|
Thus, your preschooler will remain in constant motion until acted on by complete exhaustion. At which point s/he will drop in his/her tracks.
(But generally not without a complete meltdown just prior to drop-age [See Newton's 2nd law]).
See for example:
Newton's 2nd law:
|The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma.|
In other words, the relationship between the size of your child's meltdown (m), the speed at which s/he is going just prior to the meltdown (a), and the force (f) of the exhaustion is:
F = ma
Exhaustion = (meltdown)(accelerated speed)
Newton's 3rd law:
|For every action there is an equal and opposite reaction.|
Action: Your child announces that instead of a cookie for breakfast (yes, I've done that) or a trip to the splash park, she would like her special treat for staying in her bed to be a trip to the botanical gardens to see the plants.
(This announcement immediately instills a sense of liberal pride in a parent, i.e., I have created a being that appreciates nature over processed foods and artificial outdoor play spaces)
Reaction: The next morning she gives herself (another) hair cut.
The correlary to the 3rd law can be seen in your child's response to your request that she put her dirty gardening gloves outside where they belong:
Child's response: Dammit!