Inertia The First Law is sometimes called the law of inertia. We define inertia as the tendency of an object to remain at a constant velocity, or its resistance to being accelerated. Inertia is a fundamental property of all matter and is important to the definition of mass. Newton’s Second Law To understand Newton’s Second Law, you must understand the concept of mass. Mass is an intrinsic scalar quantity: it has no direction and is a property of an object, not of the object’s location. Mass is a measurement of a body’s inertia, or its resistance to being accelerated. The words mass and matter are related: a handy way of thinking about mass is as a measure of how much matter there is in an object, how much “stuff” it’s made out of. Although in everyday language we use the words mass and weight interchangeably, they refer to two different, but related, quantities in physics. We will expand upon the relation between mass and weight later in this chapter, after we have finished our discussion of Newton’s laws. We already have some intuition from everyday experience as to how mass, force, and acceleration relate. For example, we know that the more force we exert on a bowling ball, the faster it will roll. We also know that if the same force were exerted on a basketball, the basketball would move faster than the bowling ball because the basketball has less mass. This intuition is quantified in Newton’s Second Law:
Stated verbally, Newton’s Second Law says that the net force, F, acting on an object causes the object to accelerate, a. Since F= macan be rewritten as a= F/m, you can see that the magnitude of the acceleration is directly proportional to the net force and inversely proportional to the mass, m. Both force and acceleration are vector quantities, and the acceleration of an object will always be in the same direction as the net force. The unit of force is defined, quite appropriately, as a newton (N). Because acceleration is given in units of m/s2 and mass is given in units of kg, Newton’s Second Law implies that 1 N = 1 kg · m/s2. In other words, one newton is the force required to accelerate a one-kilogram body, by one meter per second, each second. Newton’s Second Law in Two Dimensions With a problem that deals with forces acting in two dimensions, the best thing to do is to break each force vector into its x- and y-components. This will give you two equations instead of one:
The component form of Newton’s Second Law tells us that the component of the net force in the direction is directly proportional to the resulting component of the acceleration in the direction, and likewise for the y-component. Newton’s Third Law Newton’s Third Law has become a cliché. The Third Law tells us that: To every action, there is an equal and opposite reaction. What this tells us in physics is that every push or pull produces not one, but two forces. In any exertion of force, there will always be two objects: the object exerting the force and the object on which the force is exerted. Newton’s Third Law tells us that when object A exerts a force Fon object B, object B will exert a force –F on object A. When you push a box forward, you also feel the box pushing back on your hand. If Newton’s Third Law did not exist, your hand would feel nothing as it pushed on the box, because there would be no reaction force acting on it. Anyone who has ever played around on skates knows that when you push forward on the wall of a skating rink, you recoil backward.英语作文
【在百度搜索更多与“Newton’sLaws”相关英语作文】