Motion in a Straight Line

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Key Concepts of Motion

Displacement, speed, velocity and acceleration are fundamental concepts when describing motion in a straight line. You need to know how they link together.

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  • The displacement of an object, s, is the distance and direction from an object's starting position to its final position.
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Velocity and speed

  • The velocity of an object, v, is the speed and direction an object is travelling.
  • It is the rate of change of displacement:
    • v=ΔsΔtv = \frac{\Delta s}{\Delta t}
  • Speed is the magnitude of the velocity.
  • Instantaneous speed/velocity is the speed/velocity of an object at a given instant in time.
  • Average speed/velocity is the total distance/displacement divided by the total time taken.
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  • The acceleration of an object, a, is the rate (and direction) at which its velocity changes:
    • a=ΔvΔta = \frac{\Delta v}{\Delta t}
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Delta symbol

  • Delta, Δ, is the symbol meaning "change in".
  • For example, Δs means change in displacement.

Uniform Acceleration Equations

These four equations describe motion along a straight line with uniform (constant) acceleration or deceleration.

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Using the equations

  • You will often be asked questions involving the 5 key concepts of motion in a straight line:
    • s, displacement
    • u, initial velocity
    • v, final velocity
    • a, acceleration
    • t, time
  • Usually you will be given three and asked to calculate a fourth using the 'suvat' equations, which are as follows...
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The equations

  • v=u+atv = u + at
  • s=(u+v2)ts =(\frac{u + v}{2})t
  • s=ut+12at2s = ut + \frac12 at^2
  • v2=u2+2asv^2 = u^2 + 2as

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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