Both forces and lengths count
Teaching Guidance for 11-14
Not just bigger forces
Wrong Track: The force on this side is bigger so it must go down.
Right Lines: To predict what will happen with a lever you need to consider both the force and the distance on either side of the pivot.
Strength of force and length from the pivot
Thinking about the learning
With levers you must pay attention to both the size of the forces acting and the perpendicular lengths from the pivot (the length from the pivot to the line of action of the force).
Thinking about the teaching
So that pupils take length and force equally seriously make sure that both are emphasised (marked and labelled clearly) in any diagrams that you draw of levers.