9TH GRADE · WORK AND ENERGY
Work, power and energy conservation
Kinetic and potential energy in combined problems.
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
Mechanical energy
The sum of kinetic and potential energy describes the ability of a system to do mechanical work.
Kinetic energy is related to speed, and potential energy is related to position or deformation.
Work of force
The work done by a constant force depends on its modulus, displacement and the angle between them.
A force perpendicular to the speed changes the direction of movement, but at this moment does not perform mechanical work.
Mechanical Energy Conservation
Under the action of only conservative forces, the sum of kinetic and potential energies remains constant.
During friction, mechanical energy decreases, but the total energy is retained and turns into internal energy.
Physical quantities
Work of force
Energy transferred by a constant force during movement.
Unit: joule ·
Power
Mechanical work per unit of time.
Unit: watt ·
Kinetic energy
The energy of a body due to its speed.
Unit: joule ·
Potential energy
Interaction energy depending on body position.
Unit: joule ·
Height
The vertical distance from the body to the selected zero level.
Unit: meter ·
Lesson formulas
Constant force work
Work is equal to the product of force, displacement and the cosine of the angle between them.
Mechanical power
Power is equal to mechanical work divided by execution time.
Kinetic energy
Kinetic energy is equal to half the product of mass and the square of velocity.
Potential energy of the Earth
Potential energy is equal to the product of mass, g and height above the selected level.
Mechanical Energy Conservation
The sum of kinetic and potential energies is constant without friction losses.
Related formulas
The same formulas in the reference, with symbols and units.