Edexcel IGCSE Physics: Double Science 复习笔记: 1.1.5 Velocity-Time Graphs

Edexcel IGCSE Physics: Double Science 复习笔记: 1.1.5 Velocity-Time Graphs

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

     

 

 

5.6.11-Velocity-Time-Graph

 

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

     

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

     

 

velocity-time-graphs

 

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

 

Gradient of a Velocity-Time Graph

 

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

 

acceleration-is-gradient

 

 

5.6.11-Velocity-Time-Gradient

 

How to find the gradient of a velocity-time graph

 

 

Worked Example

Tora is training for a cycling tournament.

The velocity-time graph below shows her motion as she cycles along a flat, straight road.

1.1.5-WE-V-T-graph-Question-image

(a) In which section (A, B, C, D, or E) of the velocity-time graph is Tora’s acceleration the largest?(b) Calculate Tora’s acceleration between 5 and 10 seconds.

 

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:

     

1.1.5-WE-V-T-graph-Solution-image

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

     

 

 

Exam Tip

Use the entire slope, where possible, to calculate the gradient. Examiners tend to award credit if they see a large gradient triangle used - so remember to draw 'rise' and 'run' lines directly on the graph itself!

转载自savemyexams

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