When water fills a container at a constant rate, the shape of the container determines the shape of the graph of depth against time.
- Cylinder (uniform width): straight line — depth increases at a constant rate
- Wider at the top: graph curves and becomes less steep as water spreads over a larger area
- Narrower at the top: graph curves and becomes steeper as the same flow fills a smaller cross-section faster
- Vase shape (wide-narrow-wide): graph is steep, then shallow, then steep again
Tip to remember: Imagine pouring water in. If the container gets wider, the depth rises more slowly (shallower gradient). If it gets narrower, depth rises faster (steeper gradient).
This deep dive covers Container Filling Graphs (Water Problems) within Real-Life Graphs for GCSE Mathematics. Revise Real-Life Graphs in Graphs for GCSE Mathematics with 14 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 4 of 10 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Real-Life Graphs
On a distance-time graph, what does a horizontal (flat) section represent?
A distance-time graph shows a section with a negative gradient. Explain what a negative gradient means in the context of a distance-time graph.