4.6 Problem-Solving Strategies

4.6 Problem-Solving Strategies

  • Earth is nearly an insturment because of its slow rotation.
    • The effect just described is an example of how you must perform precise experiments to observeNewton's laws.
    • The effects of weather systems and ocean currents can be observed on a large scale.
  • The crucial factor in determining whether a frame of reference is in fact in motion is whether it rotates relative to a known insturment frame.
    • All phenomena discussed in this text are considered in frames.
  • There are a number of real forces that are not discussed in this section, such as lift and thrust.
    • It is not necessary to discuss every type of force because they are more specialized.
    • To ask where the basic simplicity we seek to find in physics is in the long list of forces is natural.
    • The answer to both questions is yes, as will be seen in the next section and in the treatment of modern physics later in the text.
  • When trying to push a filing cabinet, look at the forces at work.
    • If you apply an applied force, you can see the force acting on the cabinet.
    • The forces, position, velocity, and acceleration are shown in the charts.
    • You can see a free-body diagram of all the forces.
  • Success in problem solving requires understanding and applying physical principles, as well as passing exams.
    • The basics of problem solving are followed, but specific strategies useful in applying the laws of motion are emphasized.
    • The techniques reinforce concepts that are useful in other areas of physics.
    • Many problem-solving strategies are stated in the worked examples, and so the following techniques should reinforce skills you have already begun to develop.
  • Identifying the physical principles is the first thing to do.
    • If the problem involves forces, it is important to draw a careful sketch of the situation.
  • The force of a breeze is assumed to be negligible.
    • We draw a free-body diagram after defining the system of interest.
  • If Tarzan is not moving, it is obvious.
  • What is known or inferred from the problem is what needs to be determined.
    • List knowns and unknowns.
    • Determine the system of interest.
    • The decision is crucial since the second law only involves external forces.
    • It is possible to determine which forces are external and which are internal once the system of interest has been identified.
    • Newton's third law can be used to determine whether forces are exerted between components of a system or between the system and something outside.
    • The system of interest depends on the question we need to answer.
    • This choice develops into an almost unconscious process with practice.
    • In later chapters, skill in clearly defining systems will be beneficial.
  • Force is shown on free-body diagrams.
    • Several of these were drawn in worked examples.
    • There are no internal forces shown in a free-body diagram.
  • Newton's second law can be applied to solve a problem if a free-body diagram is drawn.
    • This is done for a situation.
    • Once external forces are clearly identified in free-body diagrams, it should be easy to put them into equation form and solve for the unknown.
    • If the problem is one-dimensional, then they add parallel forces.
    • If the problem is two-dimensional, it must be broken down into two problems.
    • The force vectors are projected onto the axes for convenience.
    • The choice of axes can simplify the problem.
    • A set of axes with one axis parallel to the incline is the most convenient.
    • If it's known, it's easy to make one axis parallel to the direction of motion.