The question asked for the definition of a joule. Let’s state, and restate, the elementary concepts regarding this definition...
One joule is equivalent to the energy expended, or work done, by a force of one newton accelerating a one-kilogram mass through a distance of one meter in one second. Essentially, a one-newton force, acting on a one-kilogram mass, will accelerate that 1-kg mass through one meter in one second. One newton is the force, one kilogram is the mass, and one meter is the distance moved in one second time; one joule is the energy expended, or work done, in this action. This energy expenditure is equal to exactly one watt.
Work occurs through a force acting over a distance. Energy is expended. Therefore, one joule is the work done, or energy expended, when a force of one newton acts through a distance of one meter. The energy required to complete this action is exactly one watt. If this energy expenditure happens in one second, then it is defined as one joule/second or one watt-second, or one watt/second. These units are typically given as J/s and W-s, or W/s. Also note the outcome: our 1-kg mass has a velocity of one meter per second, and if the one newton force continues, the rate of acceleration will continue at 1 meter per second per second, which is the same as one meter per second squared.
Consequently, a force of one newton acting on a 100 kilogram mass will accelerate that 100 kilogram mass through a distance of one centimeter in one second. The energy expenditure in doing so will still be equal to one joule. Note, however, in this case the mass is 100 times as great as the previously stated 1 kg, yet the distance moved is one one-hundredth of that previously stated distance of 1 m. Everything is in proportion. The energy expenditure, one joule, or one watt, is the same.
We need to also understand that concepts like heavy are related to weight, not mass. When we are talking about mass in the essence of definitions in physics we are talking about actions imparted on objects having mass (not weight) in a frame of reference without gravity. In such a frame, we can sense mass through momentum; if the object is hard to move, it is massive.
Or, if gravity is present, we are talking about the force of gravity acting on objects having mass where such objects are accelerated by gravity in free fall, or where such objects are stationary and exert a force on a stationary, horizontal platform (i.e. the force of weight, if massive they are heavy), or where objects are accelerated by gravity along a frictionless inclined plane.
Students in elementary physics classes are asked to make measurements of force, acceleration, and mass, using the classical definitions given above. The tools used in these determinations are an air table with a measured metric grid, an air rail with an attendant metric scale, a kilogram-mass air puck along with others of various masses, a spring scale, a timed-repeater strobe, and a camera for time exposures of strobe-lit experiments on the air table or rail, or for an object in free fall.
Aspects of force, mass, and acceleration, such as the resultant velocity an object gains, and distance an object is displaced, are presented to the students through the use of the differential and integral calculus, and the analysis of their measurements. These realizations are essential to understanding the concepts of potential and kinetic energy and their relation to force, mass, and acceleration.
Classic definitions of joule, a unit of work, can be found in any physics text, or in the following reference -
Sims, Frank, Engineering Formulas: Conversions, Definitions, and Tables. Industrial Press, Inc., New York, 1996. 386 pp.