This is demonstrated by the fact that the teacher does not feel the hammer blow. Due to the large mass of the books, the force of the hammer is sufficiently resisted (inertia). A wooden board is placed on top of the books and a hammer is used to drive a nail into the board. The demonstration goes as follows: several massive books are placed upon a teacher's head. The brick that offers the least resistance is the brick with the least inertia - and therefore the brick with the least mass (i.e., the Styrofoam brick).Ī common physics demonstration relies on this principle that the more massive the object, the more that object resist changes in its state of motion. 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. Yet one brick consists of mortar and the other brick consists of Styrofoam. Suppose that there are two seemingly identical bricks at rest on the physics lecture table. A more massive object has a greater tendency to resist changes in its state of motion. The more inertia that an object has, the more mass that it has. Mass is that quantity that is solely dependent upon the inertia of an object. But do some objects have more of a tendency to resist changes than others? Absolutely yes! The tendency of an object to resist changes in its state of motion varies with mass. All objects have this tendency - they have inertia. Mass as a Measure of the Amount of InertiaĪll objects resist changes in their state of motion. an object in motion would continue in motion. And if the opposing incline was not even inclined at all (that is, if it were oriented along the horizontal), then. Galileo's reasoning continued - if the opposite incline were elevated at nearly a 0-degree angle, then the ball would roll almost forever in an effort to reach the original height. If the slope of the opposite incline were reduced, then the ball would roll a further distance in order to reach that original height. Galileo further observed that regardless of the angle at which the planes were oriented, the final height was almost always equal to the initial height. Galileo postulated that if friction could be entirely eliminated, then the ball would reach exactly the same height. Galileo reasoned that any difference between initial and final heights was due to the presence of friction. If smoother planes were used, the ball would roll up the opposite plane even closer to the original height. In experiments using a pair of inclined planes facing each other, Galileo observed that a ball would roll down one plane and up the opposite plane to approximately the same height. Galileo reasoned that moving objects eventually stop because of a force called friction. Galileo, a premier scientist in the seventeenth century, developed the concept of inertia. But if left to itself, a moving object would eventually come to rest and an object at rest would stay at rest thus, the idea that dominated people's thinking for nearly 2000 years prior to Newton was that it was the natural tendency of all objects to assume a rest position. Moving objects, so it was believed, would eventually stop moving a force was necessary to keep an object moving. The dominant thought prior to Newton's day was that it was the natural tendency of objects to come to a rest position. Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. Inertia: the resistance an object has to a change in its state of motion. This tendency to resist changes in their state of motion is described as 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 unless acted upon by an unbalanced force." Objects tend to "keep on doing what they're doing." In fact, it is the natural tendency of objects to resist changes in their state of motion.
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