![]() ![]() ![]() We add all the vectors using our "head-to-tail" method to find the net force.Īgain, we start at the origin and end at the origin, meaning that the net force vector is zero. Imagine the origin as some object, and the vectors each represent a force on the object. Let's try this with a slightly more complicated (but similar) set of vectors. Thus, the tail and head of the resulting vector are both at the origin, meaning that it is a vector of magnitude zero. Note that if we follow the vectors like a path, we start at the origin and end at the origin. Since vectors have no location, what if we simply attach the tail of one vector to the head of another? Let's use the following graphical approach we'll simply translate one of the vectors such that its tail is at the same point as the head of the other vector, as shown below. Note from our example above that two vectors equal in magnitude and opposite in direction sum to zero. What happens in cases where multiple forces have different magnitudes and directions? To handle this case, we must determine how to add (and subtract) vectors. The above case is simple the forces are equal in magnitude and opposite in direction, so it is fairly obvious that they cancel. These two situations are illustrated below. If the table is removed, however, the net force is downward because of gravity-the object then falls. In this latter case, the table exerts an upward force on the object that exactly matches gravity-the object therefore remains at rest, because the net force is zero. For instance, gravity tends to pull an object down towards the Earth, but if that object is supported by a table, for instance, then it doesn't fall. What is a net force? A net force is the sum of all the forces acting on an object. A common way of stating this principle is that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, unless acted upon by a net force. Newton's first law of motion (sometimes called the law of inertia ) states that if no net force acts on an object, then that object will not experience a change in its motion (that is, an acceleration). The direction of the acceleration can be parallel to the velocity (which increases the speed of the object in its "forward" direction), antiparallel (opposite in direction) to the velocity (which decreases the speed of the object in its "forward" direction), or it can be at an angle oblique to the velocity (which causes the object to change its "forward" direction). Acceleration is simply the rate of change of the velocity acceleration also has a magnitude and a direction. Likewise, acceleration can be represented using vectors. We will consider forces in terms of Newton's laws of motion, and in doing so, we will further discuss the properties of vectors and how they can be used to study the motion of objects.įorce, Vectors, and Newton's First Law of MotionĪnother important quantity that we will represent using vectors is velocity, which is the speed of an object in a particular direction. ![]() Thus, a force is a prime candidate for representation as a vector. We can think of forces as being stronger or weaker (that is, they have a magnitude), and we can think of forces as being directed one way or another (that is, they have direction). A force, then, is an influence on the motion (or lack thereof) of an object. We can see forces at work when an object falls under the influence of gravity, or when two billiard balls collide, causing changes in their motion. Although we may have a difficult time attempting to define this term, we have a pretty good idea of what is meant when someone talks of "applying a force" to some object. O Apply vectors and their sums to understanding Newton's first law of motionĪ fundamental concept in physics is the idea of a force. O Recognize the relationship between a net force and the sum of vectors O Newton's first law of motion (law of inertia) ![]()
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