Forces, moments and equilibrium

What this module covers

• Resolve a force into horizontal and vertical parts
• Work out the moment of a force about a point, using the perpendicular distance
• Recognise a couple and know why its moment is the same about every point
• Apply the three equations of plane equilibrium and say what each one means physically
• Say what each support restrains and what reaction it therefore provides
• Draw a free-body diagram with every force on it
• Replace a distributed load with its resultant in the right place
• Find reactions using the three equations, and check them
• Interpret a negative reaction as uplift

Lessons

1. 2.1

   Forces and resolving them

   Vectors, components and resultants — the arithmetic behind everything else.

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2. 2.2

   Moments, couples and equilibrium

   Turning effects and the three equations that keep a body still.

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3. 2.3

   Supports and free-body diagrams

   What each support allows, and how to draw the picture you actually calculate from.

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4. 2.4

   Finding the reactions

   Using the three equations in the right order, and checking the answer.

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