PH02-02 Physics Coming soon
Speed at an instant from a tangent (Higher)
PH02-02
This lesson is coming soon.
In this lesson
Find the speed of an accelerating object at one particular moment by drawing a tangent to the curve of its distance-time graph and taking the gradient of that tangent.
What it covers
- Why a curve on a distance-time graph means the speed is changing: the gradient is different at every point, so 'the speed' is not one number any more
- The difference between an AVERAGE speed over an interval and the speed at an INSTANT, said in those words, with both calculated for the same curve so the two numbers visibly differ
- Drawing the tangent: a ruler laid so it touches the curve at the one point and nowhere else, with the curve falling away equally on both sides, drawn LONG so the triangle can be big
- Taking the gradient of the tangent exactly as PH02-01 took the gradient of a line - change in distance over change in time, triangle on the tangent, corners on gridlines, unit at every step
- That the answer is an ESTIMATE: two careful students get slightly different tangents and slightly different values, and both can be right within a tolerance
- That this is the one method in the chapter that gets a number out of a curve without any equation at all
Key words
For: AQA GCSE 8463
On the specification
| Board | Spec | Statement |
|---|---|---|
| AQA GCSE 8463 | 4.5.6.1.4b | The distance–time relationship |
For teachers
This GCSE Physics lesson teaches speed at an instant from a tangent (Higher). By the end, students should be able to find the speed of an accelerating object at one particular moment by drawing a tangent to the curve of its distance-time graph and taking the gradient of that tangent. It works through two worked examples and the mistakes examiners report.