Draw something similar to which has more mass in density. For example, a bowling ball and a volley ball. Both substances are similar in size but the bowling. All feels heavier than the volley ball. Label the volleyball for less density and the bowling ball with more density.
The efficiency of a machine indicates how well its input energy is converted to useful output energy or work. It is a major factor in the usefulness of a machine and is the fraction or percentage of the output divided by the input.
According to the Law of Conservation of Energy, the total output energy or work must equal the total input energy. However, some of the input energy does not contribute to the output work and is lost to such things as friction and heat.
Examples of machine efficiency include a lever, automobile, and perpetual motion machine.