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A body remains at rest, or in motion at a constant speed in a straight line, except insofar as it is acted upon by a force. At any instant of time, the net force on a body is equal to the body's acceleration multiplied by its mass or, equivalently, the rate at which the body's momentum is changing with time.
Inertia is the natural tendency of objects in motion to stay in motion and objects at rest to stay at rest, unless a force causes the velocity to change. It is one of the fundamental principles in classical physics, and described by Isaac Newton in his first law of motion (also known as The Principle of Inertia). [1]
A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force. (This is known as the law of inertia .) Force ( F → {\displaystyle {\vec {F}}} ) is equal to the change in momentum per change in time ( Δ m v → Δ t {\displaystyle {\frac {\Delta m{\vec {v}}}{\Delta t}}} ).
Hence, with respect to an inertial frame, an object or body accelerates only when a physical force is applied, and (following Newton's first law of motion), in the absence of a net force, a body at rest will remain at rest and a body in motion will continue to move uniformly—that is, in a straight line and at constant speed.
2: By its intrinsic force (alone) every body would progress uniformly in a straight line to infinity unless something external hinders that. (Newton's later first law of motion is to similar effect, Law 1 in the Principia.) 3: Forces combine by a parallelogram rule. Newton treats them in effect as we now treat vectors.
Motion (also path or trajectory) is a function r : Δ → R 3 that maps a point in the interval Δ from the time axis to a position (radius vector) in R 3. The above four concepts are the "well-known" objects mentioned by Isaac Newton in his Principia: I do not define time, space, place and motion, as being well known to all. [13]
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An object resting on a surface and the corresponding free body diagram showing the forces acting on the object. The normal force N is equal, opposite, and collinear to the gravitational force mg so the net force and moment is zero. Consequently, the object is in a state of static mechanical equilibrium.