______ is the external agency applied on a body to change its state of rest or uniform motion.

The correct answer is Force.

• Force is the external agency applied on a body to change its state of rest or uniform motion.

Key Points

• Newton's first law of motion:
  • Newton's first law states that if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.
    • This postulate is known as the law of inertia.
  • The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.

Additional Information

• In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter.
• Power is defined as the rate of doing work.
  • It is the ratio of work done (W) and time taken (t).
  • The SI unit of power is the watt (W), in honor of the physicist James Watt.
• In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it.