![]() ![]() Generally, just write Newton’s second law in components along the different directions.Tabber requires Javascript to function. It is almost always convenient to make one axis parallel to the direction of motion, if this is known. For example, when an incline is involved, a set of axes with one axis parallel to the incline and one perpendicular to it is most convenient. As seen in previous examples, the choice of axes can simplify the problem. We do this by projecting the force vectors onto a set of axes chosen for convenience. If the problem is two-dimensional, then it must be broken down into a pair of one-dimensional problems. ![]() If the problem is one-dimensional-that is, if all forces are parallel-then the forces can be handled algebraically. In general, once external forces are clearly identified in free-body diagrams, it should be a straightforward task to put them into equation form and solve for the unknown, as done in all previous examples. This is done in (Figure)(d) for a particular situation. Once a free-body diagram is drawn, we apply Newton’s second law. Note that no internal forces are shown in a free-body diagram. (Figure)(c) shows a free-body diagram for the system of interest. We have drawn several free-body diagrams in previous worked examples. Only forces are shown in free-body diagrams, not acceleration or velocity. As illustrated in Newton’s Laws of Motion, the system of interest depends on the question we need to answer. (See (Figure)(c).) Newton’s third law may be used to identify whether forces are exerted between components of a system (internal) or between the system and something outside (external). We can then determine which forces are external and which are internal, a necessary step to employ Newton’s second law. It is particularly crucial to identify the system of interest, since Newton’s second law involves only external forces. Whenever sufficient information exists, it is best to label these arrows carefully and make the length and direction of each correspond to the represented force.Īs with most problems, we next need to identify what needs to be determined and what is known or can be inferred from the problem as stated, that is, make a list of knowns and unknowns. Then, as in (Figure)(b), we can represent all forces with arrows. Once we have determined that Newton’s laws of motion are involved (if the problem involves forces), it is particularly important to draw a careful sketch of the situation. Let’s apply this problem-solving strategy to the challenge of lifting a grand piano into a second-story apartment. Check the solution to see whether it is reasonable.If necessary, apply appropriate kinematic equations from the chapter on motion along a straight line. Apply Newton’s second law to solve the problem.The result is a free-body diagram that is essential to solving the problem. Sketch the situation, using arrows to represent all forces.Identify the physical principles involved by listing the givens and the quantities to be calculated.Problem-Solving Strategy: Applying Newton’s Laws of Motion ![]()
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