Which of the following is NOT a unit of energy?

To determine which option is not a unit of energy, it's essential to understand what each of the provided choices represents:

• Joule is a well-established unit of energy in the International System of Units (SI). One joule is defined as the amount of energy transferred when one newton of force is applied over a distance of one meter.

• Newton, on the other hand, is a unit of force, not energy. While it is essential in mechanics and is often used to describe the force acting on an object, it does not measure energy itself.

• Calorie is another unit of energy, commonly used in the context of heat and nutrition. One calorie is the amount of energy required to raise the temperature of one gram of water by one degree Celsius.

• Watt is a unit of power, which is the rate at which energy is transferred or converted. One watt is equal to one joule per second.

In conclusion, the correct answer is identified as a unit that does not measure energy, which is the newton. The other options all relate to energy in some direct manner, either as a measurement of energy itself (joule and calorie) or as the rate of energy transfer (watt).