What is the kinetic energy of an object when it is at rest in a relativistic context?

In a relativistic context, the kinetic energy of an object is given by the equation ( KE = \gamma mc^2 - mc^2 ), where ( \gamma ) is the Lorentz factor defined as ( \gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}} ), ( m ) is the rest mass of the object, and ( c ) is the speed of light. When an object is at rest, its velocity ( v ) is zero. This results in the Lorentz factor becoming ( \gamma = 1 ).

Substituting ( \gamma = 1 ) into the kinetic energy equation simplifies it to ( KE = 1 \cdot mc^2 - mc^2 = 0 ). Therefore, the kinetic energy of an object at rest is zero because it has no motion to contribute to its kinetic energy. This aligns with classical concepts where an object's kinetic energy depends on its velocity; if the object's velocity is zero, its kinetic energy is also zero. Thus, the correct answer is that the kinetic energy equals zero when the object is at rest in a relativistic context.