7TH GRADE · WORK, POWER AND ENERGY
Levers and blocks
Arm of force, moment, lever balance and the golden rule of mechanics.
The entire theory of the lesson is collected here; you can read it without an account. In interactive mode, the same theory appears as cards, followed by questions. with checking the answer and task, and progress is saved.
Basic Concepts
Lever
A rigid body capable of rotating around a support and transmitting forces with different arms.
A long arm allows a smaller force to balance a larger force on a short arm.
Blocks and the Golden Rule
Simple mechanisms gain in power at the expense of a loss along the way and, ideally, do not provide a gain in operation.
A stationary block changes the direction of the force, and a movable block in an ideal design reduces the required force by half.
moment of force
A value equal to the product of a force by its arm and characterizing the rotating effect of the force.
The arm is the shortest distance from the axis to the line of action of the force, and not simply the length of the entire lever.
Physical quantities
moment of force
The product of the force on its arm relative to the axis.
Unit: newton meter ·
Shoulder of power
The shortest distance from the axis to the line of action of the force.
Unit: meter ·
Lesson formulas
moment of force
The moment of force is equal to the product of the force modulus and its shoulder.
Lever balance
A lever is balanced when the moments of forces rotating it in different directions are equal.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.