Mechanics

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Key words

  • String- Inextensible and has no mass
  • Particle- Has no size but does have mass
  • Rigid Body- Has size but does not change shape
  • Smooth- Has no friction
  • Rough- Has friction
  • Light- Has no mass
  • Inelastic/Inextensible- Does not stretch

Kinemetics in one dimension

  • In a Displacement-time graph, the velocity is calculated by working out the gradient  (y/x =velocity)
  • Velocity-time graphs have a gradient equivalent to acceleration. (y/x=accelration)
  • Area under a Velocity-time graph= Distance travelled
  • v=u+at
  • s=((u+v)t)/2
  • v^2=u^2+2as
  • s=ut+0.5at^2 or s=vt-0.5at^2
  •  Where s=displacement, u=initial velocity, v=final velocity, a=acceleration, t=time.
  • Formulae only work when acceleration is constant
  • Acceleration due to gravity(g)= 9.8 metres per second

Kinematics in two dimensions

  • Positions, velocities and accelerations can be expressed in the form xi+yj
  • Constant acceleration equations (shown above) can be used in two dimensions. Once in the i direction and once in the j direction. Adding both i and j together gives a vector.
  • Magnitude and Direction of vectors can be calculated using trigonometry and pythagoras.

Forces

  • Force is a vector quantity
  • Resultant force=two or more forces added together using its perpendicular components.
  • Particle is in equilibrium if resultant=0
  • Weight= mass x acceleration due to gravity (W=mg)
  • Frictional force between two surfaces in contact will act in a opposite direction to the

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