Newton’s laws of motion-Physics
Newton’s laws of motion
Newton’s
laws of motion:
Relations between the forces acting on a body and the motion of
the body, first formulated by English physicist and mathematician Sir Isaac Newton.
Newton’s first
law:
It 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.
Before Galileo it had been thought that all horizontal motion required a direct
cause, but Galileo deduced from his experiments that a body in motion would
remain in motion unless a force (such as friction) caused it to come to rest.
Newton’s second law:
It is a quantitative description of the changes
that a force can produce on the motion of a body. It states that the time rate
of change of the momentum of
a body is equal in both magnitude and direction to the force imposed on it. The
momentum of a body is equal to the product of its mass and its velocity.
Momentum, like velocity, is a vector quantity,
having both magnitude and direction.
A force applied to a body can change the
magnitude of the momentum, or its direction, or both. Newton’s second law is
one of the most important in all of physics.
For a body
whose mass m is constant,
it can be written in the form F = ma, where F (force) and a (acceleration) are
both vector quantities. If a body has a net force acting on it, it is
accelerated in accordance with the equation. Conversely, if a body is not
accelerated, there is no net force acting on it.
A
lesson proving immovable objects and unstoppable forces are one and the same.
That when two bodies interact, they apply forces to
one another that are equal in magnitude and opposite in direction. The third
law is also known as the law of action and reaction. This law is important in
analyzing problems of static equilibrium,
where all forces are balanced, but it also applies to bodies in uniform or
accelerated motion. The forces it describes are real ones, not mere bookkeeping
devices.
For example, a book resting on a table applies a downward force equal
to its weight on the table. According to the third law, the table applies an
equal and opposite force to the book. This force occurs because the weight of
the book causes the table to deform slightly so that it pushes back on the book
like a coiled spring.
In the 20th
century Newton’s laws were replaced by quantum mechanics
and relativity as
the most fundamental laws of physics. Nevertheless, Newton’s laws continue to
give an accurate account of nature, except for very small bodies such as
electrons or for bodies moving close to the speed of light. Quantum mechanics and
relativity reduce to Newton’s laws for larger bodies or for bodies moving more
slowly.
mechanics:
Newton’s laws of motion and
equilibrium
science
concerned with the motion of bodies under the action of forces, including the
special case in which a body remains at rest. Of first concern in the problem
of motion are the forces that bodies exert on one another. This leads to the
study of such topics as gravitation, electricity.
evolution:
Genetic equilibrium: the
Hardy-Weinberg law
They were, evolution could not occur. Why, then, is
the law significant if its assumptions do not hold true in nature? The answer
is that it plays in evolutionary studies a role similar to that of Newton’s
first law of motion in mechanics. Newton’s first law says that a body not acted
upon by a net external force remains at rest or maintains a constant velocity.
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