Overview
This lecture explains acceleration, how to calculate it, interpret velocity-time graphs, and determine distance from these graphs, focusing on key exam concepts.
Acceleration Basics
- Acceleration is the change in velocity of an object over a given time.
- The formula for acceleration: acceleration (m/s²) = (change in velocity [m/s]) ÷ (time [s]).
- Velocity is speed in a given direction and is a vector quantity (has magnitude and direction).
- You must memorize the acceleration formula, as it is not provided in exams.
Example Calculations
- Example: A car accelerates from 15 m/s to 35 m/s in 20 seconds; acceleration = (35 - 15) ÷ 20 = 1 m/s².
- Example: A cyclist slows from 6 m/s to 0 in 12 seconds; acceleration = (0 - 6) ÷ 12 = -0.5 m/s² (deceleration).
Velocity-Time Graphs
- The gradient (slope) of a velocity-time graph shows acceleration.
- A horizontal line means constant velocity.
- An upward slope means acceleration; a downward slope means deceleration.
- Acceleration from a graph: (final velocity - initial velocity) ÷ time.
Calculating Distance from Velocity-Time Graphs (Higher Tier)
- The area under a velocity-time graph gives the distance (displacement) in a specific direction.
- For constant acceleration, split the area under the graph into shapes (triangles, rectangles), find areas, and sum them.
- If the graph shows non-constant acceleration, estimate total area by counting and adding squares beneath the curve.
Key Terms & Definitions
- Velocity — Speed in a specified direction (vector quantity).
- Acceleration — Change in velocity per unit time (m/s²).
- Deceleration — Negative acceleration; object is slowing down.
- Displacement — Distance traveled in a specific direction.
- Velocity-Time Graph — Graph showing how velocity changes with time; gradient = acceleration, area under = displacement.
Action Items / Next Steps
- Memorize the acceleration formula.
- Practice calculation problems on acceleration and velocity-time graphs.
- For higher tier: Practice finding displacement by calculating area under velocity-time graphs.