To most people, technology seems mysterious and incomprehensible. Elementary physics, however, explains everything from GPS to hybrid cars to smoke detectors. If theoretical physicists successfully develop a unified field theory, physics will be explaining a lot more than just how your neighbor's lawn mower works. We may understand everything that's happened in the universe right back to the moment it was created.
A good course in general physics will take you through the topics listed here:
What follows was contributed by our leading staff physicist here at 24HourAnswers.com, who has a Ph.D. in astrophysics. Here, he offers bits of wisdom on various topics.
Kinematics is the study of motion. In a first year general physics course, this is one of the first topics covered in detail. Keep in mind that the point of physics is to learn a process for solving a wide variety of problems, not memorizing the solutions to individual problems. To fully understand kinematics requires a bit of foundation.
First we start with a basic unit for length (the meter) and a basic unit for time (the second). The next step is to define a speed (the ratio of the distance traveled to the length of time required) and an acceleration (the rate at which the speed is changing). The latter definition can be written as follows:
Acceleration = (change in speed) / (change in time)
a = (v – v0) / (t – t0)
where the subscript 0 refers to the initial value. Since we are free to choose our initial value for the time, it is convenient to set t0 = 0. This yields
a = (v – v0) / t
This expression can be cast into the following form
a * t = v – v0
v = v0 + a * t (1)
This is the first equation of kinematics.
In order to start with the simplest type of problem, we assume that the acceleration is constant. This can be written as an equation
(change in position) = (average speed) * (total time)
x – x0 = (1/2) * (v + v0) * t (2)
This is the second equation of kinematics. It is important to note that the first equation is general and holds true for all cases. The second equation, however, assumes constant acceleration and, as such, is only valid when the acceleration does not change.
By combining these two equations in various ways, any first year kinematics problem for two or three dimensions can be solved, given that the acceleration is constant.
Newton's First Law states that, in the absence of an outside force, an object will continue to stay in its current state of motion. This means that either (1) it will remain at rest in the current reference frame, or (2) it will continue moving in a straight line at constant speed (this is moving at constant velocity). Newton's Second Law is an equation, but it is instructive to consider it in two different forms:
Force = Mass * Acceleration
This can be thought of as the force required to give an object of some mass a specific acceleration. On the other hand, look at the equation this way:
Acceleration = Force / Mass
Try thinking about this one as the acceleration given to an object of a given mass as the result of applying an external force.
Newton's Third Law states that two objects in contact with one another exchange forces of equal magnitude in opposite directions.
Typically, there are a few general forces that are considered in a first year physics course. These are the normal force, the force of friction, the force of tension, the force of gravity, and externally applied forces (pushing a crate along the floor).
The biggest trick is simply making certain that you understand which forces act in what direction, and then adding the components up according to Newton's laws.
Students interested in kinematics should visit The Physics Classroom and Practice Questions for 2D Kinematics. Students interested in Newton's laws should visit Newton's Laws of Motion and Newton's Laws and the Causes of Motion.
Students with a general interest in physics might want to follow the American Institute of Physics and the American Journal of Physics. There is a useful general physics tutorial developed by the The Physics Classroom. In addition, there are good textbooks available from Amazon.com. These resources may also be able to offer some basic college physics homework help.
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