Models: “This is not a pipe”
x = vt is not the ball. A TOK look at what a model is, and how to test one against reality.
In 1929 the painter René Magritte painted a smoking pipe, and wrote underneath it, in French: “This is not a pipe.” He was right. It is a painting of a pipe. What is a formula like x = vt a picture of?
The message of “This is not a pipe” for physics models is that…
A model predicts x_f = 50 m, but the measured position is x_f* = 47 m. The right conclusion is…
In the car example, the constant-acceleration model gets worse over time because it leaves out…
In 4–6 sentences: choose one model from this lesson (for example x = vt or x = ½at²). Say what it leaves out, one situation where it is useful, and one where it is misleading.
On a v–t graph, the area is…
Y = vt assumes…
Key points
- • A model represents a real thing, but is not the thing: it leaves things out on purpose.
- • A model’s prediction (x_f) and the measured result (x_f*) can differ; a useful model keeps the gap small where you use it.
- • Know the range where a model works, and be careful outside it.
Formulas
- x_f = x_i + vt
- x_f = x_i + ut + ½at²
Key terms
- Model :
- a simplified representation used to describe and predict something real
- Assumption :
- something a model takes for granted, such as “no air resistance”
Common errors
- • Treating a model as if it WERE reality.
- • Throwing a model away because it is not perfect.
- • Trusting a model outside the conditions it was built for.