Moments, balance and stability
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 worked examples, 5 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why is a long spanner easier?
- The moment of a force
Read the transcript of the teaching part
Last time
Before we start: last time, in Forces and Newton’s laws of motion, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why is a long spanner easier?
A tight nut is hard to turn with a short spanner, and easy with a long one. The force is the same. What changed is the distance from the turning point. A force's turning effect depends on both.
The moment of a force
The moment of a force is its turning effect about a point, called the pivot. It equals the force multiplied by the perpendicular distance from the pivot to the line of action of the force. The unit is the newton metre, written N m. The distance must be at right angles to the force, and in metres.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Centre of gravity and stability · Centre of gravity and stability · Moment of a force · Principle of moments.
Chapter 1.5: Forces
- Balanced forces and F = ma 6 min
- Newton's third law 5 min
- Friction, drag and terminal velocity 5 min
- Thinking, braking and stopping distance 6 min
- Circular motion 5 min
- Springs: load–extension graphs 5 min
- Moments, balance and stability 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.