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Dynamics cheat sheet

my dynamics notes - 12000.org

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8.5 references<br />

1. Vibration analysis by Robert K. Vierck<br />

2. Structural dynamics theory and computation, 5th edition by Mario Paz, William Leigh<br />

3. Dynamic of structures, Ray W. Clough and Joseph Penzien<br />

4. Theory of vibration,volume 1, by A.A.Shabana<br />

5. Notes on Diffy Qs, Differential equations for engineers, by Jiri Lebl, online PDF book, chapter 2.6, oct<br />

1,2012 http://www.jirka.org/diffyqs/<br />

9 Derivation of rotation formula<br />

This formula is very important. Will show its derivation now in details. It is how to express vectors in rotating<br />

frames.<br />

Consider this diagram<br />

P<br />

r<br />

Y<br />

X<br />

r p<br />

y<br />

r o<br />

o<br />

<br />

x<br />

Moving frame of<br />

reference, attached<br />

to body of interest<br />

Absolute (or inertial frame of reference)<br />

In the above, the small axis x, y is a frame attached to some body which rotate around this axis with angular<br />

velocity ω (measured by the inertial frame of course). All laws derived below are based on the following one rule<br />

d<br />

dt r ∣<br />

∣∣∣absolute<br />

= d dt r ∣<br />

∣∣∣relative<br />

+ ω × r (1)<br />

Lets us see how to apply this rule. Let us express the position vector of the particle r p . We can see by<br />

normal vector additions that the position vector of particle is<br />

r p = r o + r (2)<br />

Notice that nothing special is needed here, since we have not yet looked at rate of change with time. The<br />

complexity (i.e. using rule (1)) appears only when we want to look at velocities and accelerations. This is when<br />

we need to use the above rule (1). Let us now find the velocity of the particle. From above<br />

ṙ p = ṙ o + ṙ<br />

49

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