Off the shore of Pusan, southern Korea, July 7, 1999 -- one F/A-18 Hornet assigned to Strike Fighter Squadron One 5 One (VFA-151) breaks the sound barrier in the skies end the Pacific Ocean. VFA-151 is deployed board USS Constellation (CVN 64).(Image credit: U.S. Navy photograph by Ensign john Gay)
Isaac Newton"s first Law of motion states, "A body at remainder will remain at rest, and also a body in motion will remain in activity unless the is acted upon by an outside force." What, then, happens to a body when an outside force is applied to it? That instance is explained by Newton"s second Law of Motion. 


According come NASA, this regulation states, "Force is equal to the change in inert per change in time. For a constant mass, force amounts to mass time acceleration." This is written in mathematical form as F = ma

F is force, m is mass and a is acceleration. The math behind this is rather simple. If you dual the force, you double the acceleration, yet if you dual the mass, you reduced the acceleration in half. 


Newton released his laws of motion in 1687, in his seminal job-related "Philosophiæ Naturalis Principia Mathematica" (Mathematical values of herbal Philosophy) in which the formalized the summary of how huge bodies relocate under the influence of outside forces. 

Newton increased upon the earlier work the Galileo Galilei, who developed the first accurate regulations of movement for masses, according to Greg Bothun, a physics professor in ~ the university of Oregon. Galileo"s experiments proved that all bodies advice at the same rate regardless of dimension or mass. Newton additionally critiqued and also expanded ~ above the job-related of Rene Descartes, who also published a collection of regulations of nature in 1644, 2 years ~ Newton was born. Descartes" legislations are very similar to Newton"s very first law of motion.

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Acceleration and also velocity

Newton"s 2nd law claims that as soon as a constant force acts upon a enormous body, it reasons it to accelerate, i.e., to adjust its velocity, at a consistent rate. In the simplest case, a force applied to an item at rest reasons it to advice in the direction of the force. However, if the thing is currently in motion, or if this instance is perceived from a relocating inertial recommendation frame, the body might appear to rate up, slow-moving down, or adjust direction depending on the direction of the force and also the directions the the object and also reference framework are relocating relative to every other.

The bold letters F and a in the equation show that force and also acceleration space vector quantities, which means they have both magnitude and direction. The pressure can it is in a solitary force or it can be the combination of an ext than one force. In this case, we would certainly write the equation as ∑F = ma

The large Σ (the Greek letter sigma) to represent the vector sum of every the forces, or the network force, acting on a body. 


It is rather difficult to imagine applying a continuous force come a body for an indefinite size of time. In most cases, pressures can just be used for a minimal time, creating what is called impulse. For a substantial body moving in one inertial reference frame without any type of other forces such as friction exhilaration on it, a particular impulse will cause a details change in that is velocity. The body might speed up, sluggish down or change direction, after which, the human body will continue moving in ~ a new constant velocity (unless, of course, the impulse causes the body to stop).

There is one situation, however, in which we do encounter a consistent force — the force due to gravitational acceleration, which causes massive bodies to exert a downward pressure on the Earth. In this case, the consistent acceleration as result of gravity is created as g, and Newton"s second Law i do not care F = mg. An alert that in this case, F and g space not conventionally written together vectors, since they are always pointing in the very same direction, down.


The product that mass time gravitational acceleration, mg, is well-known as weight, i m sorry is just an additional kind that force. Without gravity, a enormous body has no weight, and also without a substantial body, heaviness cannot develop a force. In order to get rid of gravity and lift a massive body, girlfriend must develop an upward pressure ma that is higher than the bottom gravitational pressure mg

Newton"s 2nd law in action

Rockets travel through an are encompass all 3 of Newton"s legislations of motion.

If the rocket needs to sluggish down, rate up, or adjust direction, a force is used to give it a push, generally coming indigenous the engine. The quantity of the force and the ar where that is providing the press can readjust either or both the rate (the magnitude component of acceleration) and direction.

Now that us know just how a substantial body in one inertial reference frame behaves when it subjected to an outside force, together as just how the engines developing the push maneuver the rocket, what wake up to the body the is exerting the force? That situation is explained by Newton’s 3rd Law of Motion. 

Additional reporting by Rachel Ross, Live science contributor.

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Jim Lucas is a contributing writer because that Live Science. He covers physics, astronomy and engineering. Jim graduated from Missouri State University, whereby he deserve a bachelor the science level in physics v minors in astronomy and technical writing. After ~ graduation he operated at Los Alamos nationwide Laboratory together a network equipment administrator, a technical writer-editor and also a nuclear defense specialist. In enhancement to writing, the edits clinical journal write-ups in a variety of object areas.