## 27 Mar Displacement, Velocity and Acceleration

In Kinematics, which is the study of motion, there are three key characteristics of any system which describe how this system moves. These are Displacement, Velocity and Acceleration, and they are all vector quantities related to one another.

The displacement of an object is how far the object is from a given reference point, which in FEA is often the origin of the model’s coordinate system. The inclusion of a reference point is vital as without it, the measurement would simply be describing a distance. The unit of a displacement is length, typically metre (m) or millimetre (mm).

The velocity of an object is how quickly the displacement of the same object is changing in a certain direction, in relation to time. This is described, as being the derivative of displacement with respect to time. The units of velocity are most commonly metres per second (m/s) but sometimes millimetres per second (mm/s) are used, depending on the units of displacement used.

The acceleration of an object, is in turn how fast the object’s velocity is changing, once again referencing a specific direction of travel. The acceleration is described as the second order derivative of displacement with respect to time. The units of acceleration are metres per second per second (m/s^{2}) or millimetres per second per second (mm/s^{2}) depending on what units of velocity are used.

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