The forces of friction, which oppose displacement, also carry out work when a body is moving. The work of friction is converted into heat. The greater the force of friction, the more force must be exerted to move the body. Verify how friction affects the displacement of some blocks.

Efficiency is a concept associated with work done by machines.In Physics this concept is defined as the quotient between the useful work done by the machine in a given interval of time and the total work invested in the machine during the same amount of time. The following visual summarises what efficiency is.

The area of the graph between the curve F and the X axis, represents the work carried out by the force between the two positions x0 and x. Review how to use the following visual and carry out the two proposed activities for a better understanding.

The educational resource shows a visual about gravitational potential energy: the calculation of gravitational potential energy is very easy for small heights.

Forces can carry out work. The work done by a force is different if it has the same direction and orientation as the displacement, or if its direction is different.

Teaching unit work and energy for 4 º ESO. Work (W). Energy. Work and energy. Power (P) of a force / machine.