The Relationship between Inertia and Mass
Newton's first law and friction, and; Discuss the relationship between mass and inertia. The key to understanding why, for example, a sliding box slows down. Mass and inertia are directly related but mass is not equal to inertia. Newton's First Law of Motion: Inertia. Newton's first law of motion states that "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction.
Buridan's position was that a moving object would be arrested by the resistance of the air and the weight of the body which would oppose its impetus. Despite the obvious similarities to more modern ideas of inertia, Buridan saw his theory as only a modification to Aristotle's basic philosophy, maintaining many other peripatetic views, including the belief that there was still a fundamental difference between an object in motion and an object at rest.
Buridan also believed that impetus could be not only linear, but also circular in nature, causing objects such as celestial bodies to move in a circle. Buridan's thought was followed up by his pupil Albert of Saxony — and the Oxford Calculatorswho performed various experiments that further undermined the classical, Aristotelian view.
Their work in turn was elaborated by Nicole Oresme who pioneered the practice of demonstrating laws of motion in the form of graphs. Shortly before Galileo's theory of inertia, Giambattista Benedetti modified the growing theory of impetus to involve linear motion alone: Classical inertia[ edit ] Galileo Galilei The principle of inertia which originated with Aristotle for "motions in a void" states that an object tends to resist a change in motion.
According to Newton, an object will stay at rest or stay in motion i. The Aristotelian division of motion into mundane and celestial became increasingly problematic in the face of the conclusions of Nicolaus Copernicus in the 16th century, who argued that the earth and everything on it was in fact never "at rest", but was actually in constant motion around the sun.
A body moving on a level surface will continue in the same direction at a constant speed unless disturbed.
Inertia and Mass
The first physicist to completely break away from the Aristotelian model of motion was Isaac Beeckman in Unless acted upon by a net unbalanced force, an object will maintain a constant velocity.
Note that "velocity" in this context is defined as a vectorthus Newton's "constant velocity" implies both constant speed and constant direction and also includes the case of zero speed, or no motion. Since initial publication, Newton's Laws of Motion and by inclusion, this first law have come to form the basis for the branch of physics known as classical mechanics.
Kepler defined inertia only in terms of a resistance to movement, once again based on the presumption that rest was a natural state which did not need explanation.
Using Inertia to Measure Mass
It was not until the later work of Galileo and Newton unified rest and motion in one principle that the term "inertia" could be applied to these concepts as it is today.
In fact, Newton originally viewed the phenomenon he described in his First Law of Motion as being caused by "innate forces" inherent in matter, which resisted any acceleration. Given this perspective, and borrowing from Kepler, Newton attributed the term "inertia" to mean "the innate force possessed by an object which resists changes in motion"; thus, Newton defined "inertia" to mean the cause of the phenomenon, rather than the phenomenon itself.
However, Newton's original ideas of "innate resistive force" were ultimately problematic for a variety of reasons, and thus most physicists no longer think in these terms. As no alternate mechanism has been readily accepted, and it is now generally accepted that there may not be one which we can know, the term "inertia" has come to mean simply the phenomenon itself, rather than any inherent mechanism.
Thus, ultimately, "inertia" in modern classical physics has come to be a name for the same phenomenon described by Newton's First Law of Motion, and the two concepts are now considered to be equivalent.
Slide a book across a table and watch it slide to a rest position. The book in motion on the table top does not come to a rest position because of the absence of a force; rather it is the presence of a force - that force being the force of friction - that brings the book to a rest position.
In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! Or at least to the end of the table top. A force is not required to keep a moving book in motion.
In actuality, it is a force that brings the book to rest. Mass as a Measure of the Amount of Inertia All objects resist changes in their state of motion.
All objects have this tendency - they have inertia. But do some objects have more of a tendency to resist changes than others?
The tendency of an object to resist changes in its state of motion varies with mass.
Inertia - Wikipedia
Mass is that quantity that is solely dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion. Suppose that there are two seemingly identical bricks at rest on the physics lecture table.
Yet one brick consists of mortar and the other brick consists of Styrofoam. Without lifting the bricks, how could you tell which brick was the Styrofoam brick?
You could give the bricks an identical push in an effort to change their state of motion. The brick that offers the least resistance is the brick with the least inertia - and therefore the brick with the least mass i.
A common physics demonstration relies on this principle that the more massive the object, the more that object resist changes in its state of motion. The demonstration goes as follows: A wooden board is placed on top of the books and a hammer is used to drive a nail into the board.