Задание 3. (10 баллов). 1. The purpose of a free-body force diagram is to assist you in trying to determine the net force acting on a body

3.1 Electromagnetic wavesare predicted by … equations. A) Maxwell’s B) Ampere’s C) Lorentz’s D) Faraday’s E) Hertz’s

3.2 An isolated system that is not affected by any external influences is called A) Closed system B) Law of conservation of energy C) Conservative system D) Work E) Power

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1. The purpose of a free-body force diagram is to assist you in trying to determine the net force acting on a body. It is only the net force to which Newton's Second Law applied and not each individual force seperately.

Useful questions to reflect on are:
How shall I define the system?

What are the forces acting on the system?

In which directions are they pushing or pulling on the system?

Do I have them all? Do I have too many?

Are any of the forces I have sketched non-existent? What is the source of the force?

Constructing a free-body force diagram:
* Select an object or group of objects to focus on as the "body", i.e. the system.

* Sketch the body by itself, "free" of its surroundings. The body could be represented by a single point located at the body's center of mass.

* Draw only those forces that are acting directly on the body. Include both the magnitude and the direction of these forces.

* Except for rotational problems, you can normally sketch the forces as though they were acting through a single point at the center of mass of the body. It is useful to draw the force-vectors with their tails at the center of mass.

* Do not include any forces that the body exerts on it surroundings; they do not act on the body.

*For a compound body you do not need to include any internal forces acting between the body's subparts, since these internal forces come in action-reaction pairs which cancel each other out because of Newton's Third Law.

*Choose a coordinate system and sketch it on the free-body diagram. If you choose one of the axes to be parallel to the object's acceleration, it can sometimes simplify the equations you have to solve.

2.A free body diagram, sometimes called a force diagram, is a pictorial device, often a rough working sketch, used by engineers and physicists to analyze the forces and moments acting on a body. The body itself may consist of multiple components, an automobile for example, or just a part of a component, a short section of a beam for example, anything in fact that may be considered to act as a single body, if only briefly. A whole series of such diagrams may be necessary to analyze forces in a complex problem. The free body in a free body diagram is not free of constraints, it is just that the constraints have been replaced by arrows representing the forces and moments they generate.

3.In physics, net force is the overall force acting on an object. In order to calculate the net force, the body is isolated and interactions with the environment or other constraints are represented as forces and torques in a free-body diagram.

The net force does not have the same effect on the movement of the object as the original system forces, unless the point of application of the net force and an associated torque are determined so that they form the resultant force and torque. It is always possible to determine the torque associated with a point of application of a net force so that it maintains the movement of the object under the original system of forces.

With its associated torque, the net force becomes the resultant force and has the same effect on the rotational motion of the object as all actual forces taken together. It is possible for a system of forces to define a torque-free resultant force. In this case, the net force when applied at the proper line of action has the same effect on the body as all of the forces at their points of application. It is not always possible to find a torque-free resultant force.

4. The photoelectric effect is the observation that many metals emit electrons when light shines upon them. Electrons emitted in this manner can be called photoelectrons. The phenomenon is commonly studied in electronic physics, as well as in fields of chemistry, such as quantum chemistry or electrochemistry.

The theory of the photoelectric effect must explain the experimental observations of the emission of electrons from an illuminated metal surface.

For a given metal, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted. This frequency is called the threshold frequency. Increasing the frequency of the incident beam, keeping the number of incident photons fixed (this would result in a proportionate increase in energy) increases the maximum kinetic energy of the photoelectrons emitted. Thus the stopping voltage increases. The number of electrons also changes because the probability that each photon results in an emitted electron is a function of photon energy. If the intensity of the incident radiation of a given frequency is increased, there is no effect on the kinetic energy of each photoelectron.

5.Pascal's law or the principle of transmission of fluid-pressure is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same. The law was established by French mathematician Blaise Pascal.

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