10TH GRADE · CONSERVATION LAWS
Work, power and energy
Work of forces, types of mechanical energy and the law of conservation.
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 work
Transfer of energy by force when moving the point of its application.
The work shows how much energy the force transferred to the body: it is positive in the direction of movement and negative against it.
Mechanical energy
The sum of the kinetic and potential energies of the system.
Kinetic energy is associated with motion, potential energy is associated with position and interaction; in the process they can transform into each other.
Law of conservation of mechanical energy
When only conservative forces act, mechanical energy is conserved.
If there is friction or an external force, the mechanical energy may change - then you need to take into account their work or the transition of energy into internal energy.
Physical quantities
Work
Energy transferred by force during movement.
Unit: joule ·
Power
Work done per unit of time.
Unit: watt ·
Kinetic energy
Energy of body movement.
Unit: joule ·
Potential energy
Energy of interaction and body position.
Unit: joule ·
Potential strain energy
Energy stored by an elastically deformed body.
Unit: joule ·
Mechanical energy
The sum of kinetic and potential energies.
Unit: joule ·
Lesson formulas
Constant force work
Work is equal to the product of force, displacement and the cosine of the angle between them.
Definition of joule
One joule is equal to the work done by a force of one newton over a path of one meter.
Work of gravity
The work done by gravity during descent is equal to the product of mass, acceleration and change in height.
Work of elastic force
The work done by the elastic force upon returning to the undeformed state is equal to the stored energy.
Power
Power is equal to work done during time and the product of force and speed in coinciding directions.
Definition of watt
One watt is equal to one joule per second.
Kinetic energy
The kinetic energy of translational motion depends on the mass and the square of the velocity.
Potential energy in a gravitational field
Potential energy depends on mass and height above the selected level.
Elastic deformation energy
The energy of an elastically deformed spring depends on the stiffness and the square of the elongation.
Mechanical Energy Conservation
The sum of potential and kinetic energies is the same in the initial and final states.
Total mechanical energy
Total mechanical energy is equal to the sum of kinetic and potential.
Work of external forces
The work done by non-conservative external forces is equal to the change in mechanical energy.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.