Edexcel IGCSE Physics 复习笔记 1.1.5 Velocity-Time Graphs

• A velocity-time graph shows how the velocity of a moving object varies with time
  • The red line represents an object with increasing velocity
  • The green line represents an object with decreasing velocity

   

Increasing and decreasing velocity represented on a velocity-time graph

Acceleration on a Velocity-Time Graph

• Velocity-time graphs also show the following information:
  • If the object is moving with a constant acceleration/deceleration
  • The magnitude of the acceleration/deceleration

   

• A straight line represents constant acceleration
• The slope of the line represents the magnitude of acceleration
  • A steep slope means large acceleration (or deceleration) - i.e. the object's speed changes very quickly
  • A gentle slope means small acceleration (or deceleration) - i.e. the object's speed changes very gradually
  • A flat line means the acceleration is zero - i.e. the object is moving with a constant velocity

   

This image shows how to interpret the slope of a velocity-time graph

• The acceleration of an object can be calculated from the gradient of a velocity-time graph

How to find the gradient of a velocity-time graph

Part (a)

Step 1: Recall that the slope of a velocity-time graph represents the magnitude of acceleration

• • The slope of a velocity-time graph indicates the magnitude of accelerationTherefore, the only sections of the graph where Tora is accelerating is section B and section D
  • Sections A, C, and E are flat – in other words, Tora is moving at a constant velocity (i.e. not accelerating)

   

Step 2: Identify the section with the steepest slope

• • Section D of the graph has the steepest slope 

    Hence, the largest acceleration is shown in section D

   

Part (b)

Step 1: Recall that the gradient of a velocity-time graph gives the acceleration

• • Calculating the gradient of a slope on a velocity-time graph gives the acceleration for that time period

   

Step 2: Draw a large gradient triangle at the appropriate section of the graph

• • A gradient triangle is drawn for the time period between 5 and 10 seconds below:

   

Step 3: Calculate the size of the gradient and state this as the acceleration

• • The acceleration is given by the gradient, which can be calculated using:

   

acceleration = gradient = 5 ÷ 5 = 1 m/s²

• • Therefore, Tora accelerated at 1 m/s² between 5 and 10 seconds