IGCSE Physics (2026-2028) - C2/25: Speed, Acceleration, Distance-Time Graph, Speed-Time Graph

Calculating Speed and Velocity
📌 Speed is defined as the distance traveled by an object per unit of time, calculated using the formula: Speed = Distance / Time.
⚙️ Common units for speed include meters per second ($\text{m/s}$) and kilometers per hour ($\text{km/h}$).
⏱️ To find time when speed and distance are known, rearrange the formula to: Time = Distance / Speed.
➕ Velocity is similar to speed but includes direction; speed is a scalar quantity, while velocity is a vector quantity.

Distance-Time Graphs Analysis
📏 The speed of an object is determined by calculating the gradient (steepness) of the distance-time graph using $m = \frac{y_2 - y_1}{x_2 - x_1}$.
💨 A steeper slope on a distance-time graph signifies a faster speed.
🛑 A horizontal line on a distance-time graph indicates that the distance is not changing over time, meaning the object is stopped.

Acceleration and Speed-Time Graphs
🚀 Acceleration is the rate of change of an object's velocity, calculated as: $a = \frac{v - u}{t}$, where $v$ is final speed, $u$ is initial speed, and $t$ is time.
⚡ The unit for acceleration is meters per second squared ($\text{m/s}^2$).
↔️ In a speed-time graph, the distance traveled is calculated by measuring the area under the graph.
📈 For a speed-time graph, acceleration is calculated using the gradient of the line segment.

Advanced Graph Interpretation
〰️ For a curved speed-time graph, acceleration at a specific time is found by drawing a tangent line at that point and calculating the gradient of that tangent.
📉 Slowing down (deceleration) on a speed-time graph is represented by a downward-sloping line as speed decreases over time.

Key Points & Insights
➡️ To calculate average speed for a multi-part journey, always use the total distance divided by the total time taken for the entire journey.
➡️ When calculating average speed, subtract any time the object was stopped from the total elapsed time if the question refers to *travel time*.
➡️ A horizontal line on a speed-time graph indicates steady speed (or zero speed if the line is on the time axis).

📸 Video summarized with SummaryTube.com on Feb 04, 2026, 16:41 UTC