AQA A Level Physics复习笔记4.3.3 SUVAT Equations

• The SUVAT equations are the equations of motion used for objects in constant acceleration
• They contain the following variables:
  • s  = displacement (m)
  • u = initial velocity (m s-1)
  • v = final velocity (m s-1)
  • a = acceleration (m s-2)
  • t = time (s)

   

• The 4 SUVAT equations are:

• These are all given on the data sheet
• All the variables, apart from time t, are vector quantities
  • This means they can either be positive or negative depending on their direction

   

• The key terms to look out for are:
  • 'Starts from rest', or if the initial velocity is not mentioned, this means u = 0
  • 'Starts from rest' also means that t = 0
  • If an object is only 'falling due to gravity' then a = g = 9.81 m s-2
  • It doesn't matter which way is positive or negative for the scenario, as long as it is consistent for all the vector quantities
    • For example, if downwards is negative then for a ball travelling upwards, s must be positive and a must be negative

     

   

• SUVAT equations are used for motion with constant acceleration in a straight line
  • For example, an object falling in a uniform gravitational field without air resistance

   

How to Use the SUVAT Equations

• Step 1: Write out the variables that are given in the question, both known and unknown, and use the context of the question to deduce any quantities that aren’t explicitly given
  • e.g. for vertical motion a = ± 9.81 m s–2, an object which starts or finishes at rest will have u = 0 or v = 0

   

• Step 2: Choose the equation which contains the quantities you have listed
  • e.g. the equation that links s, u, a and t is s = ut + ½at2

   

• Step 3: Convert any units to SI units and then insert the quantities into the equation and rearrange algebraically to determine the answer
• Sometimes the question may have to be split into two, where the SUVAT equations will have to be used twice
  • For example, if there are two masses connected over a pulley and one mass continues moving after the other has stopped