Newton's laws of motion
Newton's laws of motion
[1], [2], [3] Newton's laws of motion are 3 physical laws describing the relationship between an object's motion and forces acting on it:
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Law 1: A body is at rest or in motion at constant speed in a straight line, unless it is acted by a force.
Law 2: At any instant of time, a body's net force is its acceleration times its mass or the rate its momentum changes overtime.
Law 3: If 2 bodies exert forces on each other, they have the same magnitude but opposite directions.
Law 1: Inertia
Law 1: Inertia
Newton’s 1st Law: Inertia is the tendency to resist changes in a state of motion--any object is at rest or in uniform motion in a straight line unless compelled to change its state by an external force. If all external forces cancel each other out, then no net force is on the object. If there is no net force acting on the object, then the object keeps constant velocity.
Inertia in aerodynamics examples:
The motion of an airplane when a pilot changes the throttle setting of an engine.
The motion of a ball falling down through the atmosphere.
A model rocket being launched up into the atmosphere.
The motion of a kite when the wind changes.
Law 2: Force
Law 2: Force
Newton’s 2nd Law: Force equals to momentum change (mass times velocity) per change in time. Momentum is an object's mass (m) of an object times its velocity (V).
Law 2 formula: F = ma
F = force applied
m = object's mass
a = object's acceleration
An object's acceleration depends on its mass and how much force applies.
Suppose an plane at point '0' at location X0 and time t0m, with m0 mass and V0 velocity. An external force F to the plane above moves it to point 1 and it snew location is X1 and time t1.
Its mass and velocity changes in flight to values m1 and V1. Law 2 helps to find the new V1 and m1 values, if we know the size of force F.
Calculate the difference between point 1 and the conditions at point 0.
Law 3: Action and reaction
Law 3: Action and reaction
[3], [5] Newton’s 3rd Law: Any action (force) in nature has an equal and opposite reaction from interactions.
in nature: occur naturally/without human intervention
Law 3 formula: →FAB = -→FAB
E.g. If object A exerts a force on object B, which also exerts an equal and opposite force on object A.
Action and reaction involving aerodynamics examples:
The motion of lift from an airfoil, the air is deflected downward by the airfoil’s action, and in reaction, the wing is pushed upward.
The motion of a spinning ball, the air is deflected to one side, and the ball reacts by moving in the opposite direction.
The motion of a jet engine produces thrust and hot exhaust gases flow out the back of the engine, and a thrusting force is produced in the opposite direction
If a bus driving on a road hits a fly, both have the same force--Each force is the same size.
A gun's recoil or kickback, is the backward movement a shooter feels when the bullet is discharged.
A rifle recoils, if fired, is the result of action-reaction force pairs. A gunpowder explosion makes hot gases outward for the rifle to push forward bullets. Consistent to law 3 of motion, the bullet pushes backwards upon the rifle. The acceleration of the recoiling rifle is smaller than bullet's acceleration--The rifle's force is the bullet's force, but acceleration depends on both force and mass. Bullet has a higher acceleration due to smaller mass.
Note: acceleration and mass are inversely proportional.
History
History
[1], [2] Age 23 Newton did the gravitation theories in 1666.
1686, he presents his 3 laws of motion in the “Principia Mathematica Philosophiae Naturalis.” (Mathematical Principles of Natural Philosophy). He used them to explain motion of many physical objects and systems.
Limitations to his laws are; new theories are needed if objects move at high speed (special relativity), are very big (general relativity), or are very tiny (quantum mechanics).
1543, Nicolaus Copernicus says the Sun, instead of Earth, is universe's centre.
Then Johannes Kepler and Descartes laid a new science's foundations that replace the Aristotelian worldview from the ancient Greeks and explain workings of a heliocentric universe. In the Principia Newton created that new science. He succeeds to explain why planets' orbits are ellipses, not circles, by his 3 laws and explained more.
The series of events from Copernicus to Newton is the Scientific Revolution.
20th century, Newton’s laws are replaced by quantum mechanics and relativity as most fundamental physics law. Regardless, his laws is still gives accurate account of nature, except tiny bodies (electrons/bodies almost fast as light). Quantum mechanics and relativity reduce to the laws for larger bodies or for bodies moving slower.
Quizzes
Quizzes
[Q1] Flashcard
[Q2]
[Q3]
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