Edexcel IGCSE Physics: Double Science 复习笔记: 1.1.4 Acceleration

Edexcel IGCSE Physics: Double Science 复习笔记: 1.1.4 Acceleration

Acceleration

 

  • Acceleration is defined as the rate of change of velocity
    • In other words, it describes how much an object's velocity changes every second

     

  • The equation below is used to calculate the average acceleration of an object:

 

acceleration-equation-1

 

acceleration-equation-symbols-1

 

  • Where:
    • a = acceleration in metres per second squared (m/s2)
    • Δv = change in velocity in metres per second (m/s)
    • t = time taken in seconds (s)

     

  • The change in velocity is found by the difference between the initial and final velocity, as written below:

 

change in velocity = final velocity − initial velocity

 

Δv = v − u

  • Where:
    • v = final velocity in metres per second (m/s)
    • u = initial velocity in metres per second (m/s)

     

 

 

 

  • The equation for acceleration can be rearranged with the help of a formula triangle as shown:

5.6.10-Acceleration-Formula-Triangle

 

 

Speeding Up & Slowing Down

  • An object that speeds up is accelerating
  • An object that slows down is decelerating
  • The acceleration of an object can be positive or negative, depending on whether the object is speeding up or slowing down
    • If an object is speeding up, its acceleration is positive
    • If an object is slowing down, its acceleration is negative (sometimes called deceleration)

     

 

5.6.10-Acceleration-Examples

 

A rocket speeding up (accelerating) and a car slowing down (decelerating)

 

 

Worked Example

A Japanese bullet train decelerates at a constant rate in a straight line.The velocity of the train decreases from 50 m/s to 42 m/s in 30 seconds.

 

(a) Calculate the change in velocity of the train.

 

(b) Calculate the deceleration of the train, and explain how your answer shows the train is slowing down.

 

 

Part (a)

 

Step 1: List the known quantities

 

    • Initial velocity = 50 m/s
    • Final velocity = 42 m/s

     

 

Step 2: Write the relevant equation

 

change in velocity = final velocity − initial velocity

 

Step 3: Substitute values for final and initial velocity

 

change in velocity = 42 − 50 = −8 m/s

 

 

Part (b)

 

Step 1: List the known quantities

 

    • Change in velocity, Δv = − 8 m/s
    • Time taken, t = 30 s

     

 

Step 2: Write the relevant equation

 

acceleration-equation-symbols-1 

Step 3: Substitute the values for change in velocity and time

 

a = −8 ÷ 30 = −0.27 m/s

 

Step 4: Interpret the value for deceleration

 

    • The answer is negative, which indicates the train is slowing down

     

 

 

Exam Tip

Remember the units for acceleration are metres per second squared, m/s2In other words, acceleration measures how much the velocity (in m/s) changes every second, m/s/s.

转载自savemyexams

更多IGCSE课程
翰林国际教育资讯二维码