4.2 Equilibrium of forces

3 of 3 objectives have lessons · 0 studied · 0 secure

Lessons

The principle of moments: balancing actsFor an object in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about that same point. 5 min, not started
Equilibrium: no resultant force AND no resultant torqueAn object is in equilibrium only when the resultant force on it is zero and the resultant torque on it is zero; you need both, and together they find unknown forces. 5 min, not started
Beams, hinges and cablesFor a beam hinged to a wall and held by an angled cable, take moments about the hinge to find the tension, then resolve to find the hinge force. 5 min, not started
Closed vector trianglesThree coplanar forces in equilibrium, drawn tip to tail, form a closed triangle, so you can find unknown forces by scale drawing or trigonometry. 5 min, not started
Solving force triangles: two strings and a washing lineUse the sine rule on the closed vector triangle, or resolve in two directions, to find tensions in strings at any angles, and see why a loaded line can never be straight. 5 min, not started

3 objectives

What Cambridge says you should be able to do, in our words. Codes are the topic number plus the objective’s position.

4.2.1

State the principle of moments and apply it.

Taught in: Beams, hinges and cables, The principle of moments: balancing acts · 10 questions

4.2.2

Understand that a system with no resultant force and no resultant torque acting on it is in equilibrium.

Taught in: Beams, hinges and cables, Equilibrium: no resultant force AND no resultant torque · 6 questions

4.2.3

Represent coplanar forces in equilibrium using a vector triangle.

Taught in: Solving force triangles: two strings and a washing line, Closed vector triangles · 11 questions