Motion (Physics)
Motion in physics refers to the change in position of an object over time relative to a frame of reference. It is a fundamental concept in physics, encompassing various aspects such as distance, speed, velocity, and acceleration. Motion occurs due to the influence of forces acting upon objects, and the study of motion is divided into several branches: kinematics focuses solely on motion, dynamics examines the interplay of motion and forces, and mechanics encompasses motion, forces, and energy. Historically, significant contributions to the understanding of motion were made by figures like Aristotle, Galileo, Kepler, and Newton, each refining the concepts over time.
Newton's three laws of motion form the cornerstone of classical mechanics, explaining how objects behave in motion and the forces that affect them. These laws describe how an object remains at rest or in uniform motion unless acted upon by an external force, how force equals mass times acceleration, and how every action has an equal and opposite reaction. While these principles effectively describe motion at everyday speeds and scales, Einstein's theories of relativity and quantum mechanics introduce different rules applicable at high speeds and subatomic levels, illustrating the complexity and richness of the study of motion in physics.
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Motion (Physics)
Motion in physics is a change in the position of an object over time relative to a frame of reference. Motion is one of the fundamental building blocks of physics and can be observed in terms of distance, speed, velocity, and acceleration. For motion to occur or change, an object must be acted upon by a force, an interaction with another object. The study of motion by itself is called kinematics, the study of motion and force is referred to as dynamics, while the study of motion, force, and energy is called mechanics. In general, motion follows laws discovered by Isaac Newton in the seventeenth century. Other laws of motion take effect when examining subatomic particles or when traveling close to the speed of light.
There are generally considered to be four types of motion. Linear motion occurs when an object moves in a straight line. Rotary motion is when an object moves in a circular path, such as a wheel or a merry-go-round. Oscillating motion is when an object swings or moves side to side in a repetitive manner. Examples of this are a pendulum or the movement of a rotating fan. Reciprocating motion is a back-and-forth motion in a straight line, such as the cutting motion of a saw. Some scientists add a fifth category called random motion, which is a type of motion that does not adhere to a fixed pattern.
Brief history
In the fourth century BCE, Greek philosopher Aristotle attempted to understand the concept of motion in his scientific work The Physics, a name taken from the Greek term for "lessons on nature." To Aristotle, motion was an eternal force and involved a change from potentiality to actuality. Natural motion, he argued, was the movement of an object without being forced, such as the rising of the sun or the downward movement of a rock when it is dropped. Violent motion occurred when a "mover," or outside influence, pushed an object. While Aristotle's thinking was advanced for his time, his ideas on motion and physics were fundamentally flawed and incomplete. Nevertheless, they remained the scientific standard for almost two thousand years.
During the Renaissance, scientists began reexamining the accepted scientific methods and developed new ways to view the physical world. In the late sixteenth century, Italian astronomer Galileo Galilei recorded his own theories on motion, determining that objects dropped from a height will fall at the same speed no matter what their weight. In the early seventeenth century, German astronomer Johannes Kepler applied the concept of motion to heavenly bodies, developing his three laws of planetary motion. He found that the orbit of planets around the sun is elliptical, or oval, in shape. Kepler also said that planets move more slowly in their orbits the further they are from the sun. Despite this, he noted that a planet covers the same distance in equal intervals of time as it orbits the sun.
Overview
In 1687, English physicist Isaac Newton revolutionized science when he published the Mathematical Principles of Natural Philosophy, which included his three laws of motion. The first law states that 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 means that objects will not move, change direction, or stop moving unless they are influenced by another force. For example, a baseball on the ground will remain motionless unless it is picked up and thrown by a pitcher. If that same baseball is hit by a batter, the ball would continue to move unless it encounters another object or is slowed by the force of friction caused by the air.
Newton's second law states that the force acting on an object is equal to the mass of that object times its acceleration. The equation is written out as F=ma, with F standing for force, m for mass, and a for acceleration. Mass is the amount of matter in an object, and acceleration is the rate at which an object changes its velocity. While speed is the distance an object travels over a certain period, velocity refers to the distance an object travels over time in a given direction. According to Newton's second law, if a constant force is applied to an object, that object will accelerate at a constant rate. It also states that the more mass an object has, the more force is needed to move it. Using the baseball analogy, if a pitcher throws a baseball, it will travel toward the batter at a certain speed. Assuming the batter makes solid contact, when the ball encounters the force of the bat, it will move in a different direction at a faster speed. If a pitcher throws a softball, which has a larger mass, and the batter makes the same contact, the softball would travel at a slower speed than the baseball due to its larger mass. To move both the baseball and softball at the same speed, the batter would have to use more force on the softball.
Newton's third law states that for every action, there is an equal and opposite reaction. This means that one force is always accompanied by another, acting in the opposite direction. For example, when a rocket lifts off, its fuel ignites behind it and pushes downward at the ground, propelling it upwards.
Newton's laws of motion work very well when referring to conditions on Earth or with planetary bodies. However, German physicist Albert Einstein showed in his theories on relativity that different rules apply when traveling close to the speed of light—186,000 miles per second. Einstein's famous equation, E=mc2, means that energy (E) is equal to mass (m) times the speed of light squared (c2). At speeds approaching that of light, an object's energy will increase, as will its mass. Very small subatomic particles such as electrons, protons, neutrons, and quarks do not adhere to Newton's laws at all. They are governed by a different set of physicals laws called quantum mechanics.
Bibliography
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