Physics·General Physics · NSSCO 2.7
Moments — the turning effect of a force
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Push a door far from its hinges and it swings easily; push it near the hinges and it barely moves. That turning effect of a force is called the MOMENT. We'll define it, use the formula moment = force × perpendicular distance (measured in N m), meet the principle of moments (clockwise = anticlockwise when balanced), balance see-saws and beams with worked calculations, and describe the metre-rule experiment that proves there is no net moment on a body in equilibrium.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 2.7):
- Describe the moment of a force as a measure of its turning effect and give everyday examples (crowbar, wheelbarrow, pliers, scissors, tweezers, tongs)
- Identify the load, effort and fulcrum in everyday machines such as a spanner and a wheelbarrow
- Describe the difference between a moment and work (moment is a vector with distance perpendicular to the force; work is a scalar with distance along the force)
- Recall and use the formula moment = force × perpendicular distance from the pivot (unit N m)
- State that a system is in equilibrium when there is no resultant force and no resultant turning effect
- State and use the principle of moments (sum of clockwise moments = sum of anticlockwise moments) in simple calculations
- Describe an experiment, involving vertical forces, to verify that there is no net moment on a body in equilibrium
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Ms Elizabeth and Mike talk through the whole topic — with the figure and working drawn live.