While the person may not have made the numerical calculation we did, they intuitively knew they had to push with a force greater than the number we calculated. Newton’s first law tells us that any pushing force greater than 20 Newtons will get the piano moving. Using Newton’s first law for the x-direction, we can calculate the net frictional force to determine the minimal force the person must push with. Let’s say the frictional force between the wheels and the floor is 10 Newtons and the total friction in the bearings of the wheels is 10 Newtons. Thus, during the time when the velocity is changing, the net external force causes an acceleration, and Newton’s second law comes into play.įor the sake of completion, let’s toss some numbers into our equation to get an idea of the numerical value of the acceleration. When the person pushes with enough force to overcome the frictional forces resisting motion, the piano goes from a zero velocity to a non-zero velocity, and any change in velocity constitutes an acceleration. In the \(x\)-direction, we have the push force of the person in the positive \(x\)-direction and the force of the piano pushing back in the negative \(x\)-direction. The forces in the \(y\)-direction, as we have seen, are the force of gravity downward and the force of the floor pushing up. Let’s set up the situation in which the first law holds that is, the situation of translational equilibrium. In this example, we are interested in the moment when the person pushes the piano with just enough force to get it moving. Let’s say you have someone pushing a piano across a stage. Let’s take a look at both a one-dimensional and a two-dimensional example to illustrate some applications of Newton’s second law. As with Newton’s first law, the internal forces are not included, and it can only be applied in an inertial frame of reference. Newton’s second law can be considered an extension of the first law for the situation where the sum of the net external forces is non-zero. Since \(m\) is a positive quantity, the acceleration vector points in the same direction as the net external force vector. Newton’s second law is generally written in the form \(F=ma\), where \(F\) is the net external force causing a mass, \(m\), to undergo an acceleration, \(a\). In other words, more force generates more acceleration for a given mass, but more mass means less acceleration from a given force. Newton’s second law states the acceleration of an object is directly proportional to the net external force applied, and it is indirectly proportional to its mass. Hi, and welcome to this video on Newton’s second law of motion! In this video, we will look at Newton’s second law, compare it with his first law, and look at a couple of simple, common applications.
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