5-2 Absolute Motion
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1. Introduction
5.2 Absolute Motion
• This approach is to find velocity and acceleration (linear, rotational or both) based on the geometry of the problem.
• Steps:
• Define the positional (angle, distance) variables involved (the ones to be determined and the given ones).
• Find the positional relation containing the defined variables.
• The positional relation is usually from the geometry/configuration of the problem = using sin/cos laws, Pythagorean theorem,
Trigonometry etc.
• Differentiate to get the velocity and acceleration relations.
• Caution:
• The relation must hold for a duration of time.
• The distance/angle must be measured from a fixed point/line.
• Be careful with the signs e.g. ω is positive means θ is increasing.
5.2 Absolute Motion
Example 1: Constraint Link
2103212 Dynamics, NAV, 2012 4
5.2 Absolute Motion
Example 1: Constraint Link
Example 1: Constraint Link
5.2 Absolute Motion
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5.2 Absolute Motion
Example 2: Slotted Link
5.2 Absolute Motion
Example 2: Slotted Link
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Example 3: Slider-Crank Mechanism
Note that the acceleration is very tedious to
compute so the relative method is preferred.
