Velocity-Time Graphs

Understanding Velocity-Time Graphs

• A velocity-time graph shows how the velocity of an object changes over a period of time.
• On this type of graph, the horizontal axis (x-axis) represents time (t), while the vertical axis (y-axis) illustrates velocity (v).
• The gradient or slope of a line on a velocity-time graph signifies the acceleration of the object.

Key Aspects of Velocity-Time Graphs

• A horizontal line on a velocity-time graph demonstrates an object moving at a constant speed. Although the object is in motion, its velocity is unchanging, hence, the acceleration is zero.
• A rising straight line suggests the object is accelerating. The gradient of the line corresponds to the rate of acceleration—the steeper the line, the greater the acceleration.
• Conversely, a falling straight line implies the object is decelerating, or accelerating in the opposite direction. The steeper the line, the greater the deceleration.
• A curve on a velocity-time graph symbolises changing acceleration. A curve that is getting steeper means acceleration is increasing, whilst a curve that is getting less steep means acceleration is decreasing.

Interpreting Velocity-Time Graphs

• The slope of the line can be used to calculate the acceleration of the object. Acceleration (a) is obtained by dividing the change in velocity (Δv) by the change in time (Δt).
• Contrary to distance-time graphs, the area under the line on a velocity-time graph equates to the total distance the object has travelled. If the line is above the time axis the distance travelled is positive, if below, the distance is negative.

Plotting Velocity-Time Graphs

• To create a velocity-time graph, first gather measurements of velocity at specific time intervals. These data points can then be plotted on the graph.
• Once all the points are plotted, draw a line or curve that accurately represents the trend of the data points.

Analysing Real-Life Scenarios

• Velocity-time graphs can be utilised to break down real-world events. For instance, they can represent and analyse how a bike or car accelerates, keeps a constant speed, or decelerates during a journey.
• Understanding velocity-time graphs is crucial in making predictions about future events based on past or current data, such as predicting a vehicle’s future location based on its current speed and acceleration.