# Advice 1: How to find kinetic energy

Kinetic energy is the energy of the mechanical system, which depends on the speed of movement of each of its points. In other words, the kinetic energy represents the difference between the total energy and the rest energy of the system, that part of the total energy of the system, which is caused by movement. Kinetic energy divided by the energy of translational and rotational motion. The unit of measurement of kinetic energy in SI system is Joule.
Instruction
1
In the case of translational motion all points of the system (body) have the same speed, which is equal to the velocity of the center of mass of a body. While the kinetic energy of the system Tpost equal to:
Tpost = ? (mk Vс2)/2,
where mk is the body mass, VC is the speed of the center of mass.Thus, when the forward movement of the body kinetic energy is equal to the product of body weight to the square of the velocity of the center of mass, divided by two. The value of the kinetic energy does not depend on the direction of movement.
2
In rotational motion, when the body rotates around any axis Oz, the speed of any point determines the equation: Vk = ?hk, where hk is the distance of this point to the axis of rotation ? - the angular velocity of the body. If we substitute the equation that determines the velocity of a point at the expression and make the overall multipliers of the bracket, we will obtain the equation of the kinetic energy of the system while the rotational motion: TVR = ? (mk ?2 hk2)/2 = ? (mk hk2) ?2/2Выражение made in brackets represents the moment of inertia of the body about the axis around which the rotation of the body. Here you will receive: TVR = (Iz ?2)/2, where Iz is the moment of inertia of the body. Thus, when the rotational motion of the body, its kinetic energy is equal to the product of the moment of inertia of the body about the rotation axis to the square of its angular velocity divided in half. The direction of rotation of the body does not affect the value of its kinetic energy.
3
In the case of a perfectly rigid body is full of kinetic energy is equal to the sum of the kinetic energies of translational and rotational motion:T = (mk Vc2)/2 + (Iz ?2)/2
Note
Kinetic energy is always positive quantity.

# Advice 2 : How to calculate the amperage

Current, voltage, power and resistance are linked by defined relations. Any of these four quantities can be calculated if you know at least two others. When the other three known variables, the information becomes redundant.
Instruction
1
Before performing any calculations, be sure to move all the existing condition of the problem data to the SI system. The voltage must be expressed in volts, current in amperes, resistance in ohms, power in watts. Most often these values are used the prefixes "micro" (one millionth, sokraschenno - MK), "Milli" (one thousandth, abbreviated m), "kilo" (one thousand, abbreviated K), mega (million, abbreviated as - M) and "Giga" (one billion, short - G).
2
To find the force of the current at a known voltage and resistance, use Ohm's law to the partial circuit by the calculation according to this formula:I=U/R where I - current, U - voltage, R - resistance.
3
If you know power and resistance, use the following ratio:U=RI, P=UI, hence P=R(I^2)Hence, I^2=P/R and so I=sqrt(P/R), where I - current, P - power, R is the resistance.
4
At a known voltage and power calculations spend so:P=UI, hence I=P/U where I - current, P - power, U - voltage.
5
After the calculation is finished, set the result of SI in the units in which it is required to Express the conditions of the problem (often it is milliamperes, or microamperes).
6
If the calculations are made in the report for the laboratory work, the result of their if necessary, check on a real laboratory plant, because the voltage and force current can be changed easily, respectively, by a voltmeter and ammeter. If used with high voltage measurement be made with caution. Measure resistance by ohmmeter when the power is off installation. As for allocated load heat output, then its measure is not so easy, because it requires a calorimeter.
7
If you are studying in high school or in higher education, the teacher may require you in the design of the problem solution to calculate the error of measurements and calculations the conventional manner.

# Advice 3 : How to calculate reactive power

Reactive power current can be obtained only in circuits with alternating current, in which there are inductors, capacitors, or both. The vast majority of cases, the reactive power does not perform useful work, and is spent on generation of electromagnetic fields. Many devices specify the power factor, which is denoted Cos(φ). It is easy to calculate the reactive power consumed by the device knowing power. If such a coefficient, it can be calculated independently.
You will need
• - power factor;
• tester.
Instruction
1
To calculate the reactive power of the appliance, carefully read its documentation it should be given the power factor Cos(φ). With a multimeter measure the power consumption of the device, then from number subtract 1 power factor, and the resulting number multiply by the measured power (PP=P•(1 - Cos(φ)). The result will be the reactive power of the device. In some devices develops significant reactive power, for example, arc furnaces or welding machine AC its value can reach 40% of the nominal power.
2
If the device does not indicate the power factor, calculate the reactive power independently. For this, use a tester that is configured in the mode voltmeter, measure the voltage drop across the device, the effective value. Find out the frequency of the AC network where the connection device, for standard home network, this value is 50 Hz.
3
Switch the tester to the measurement of inductance and find out its value for this device in Henry. Then switch the tester to measure the capacity to learn it, expressed in Farads. In both cases, the tester connect a parallel device to its clips.
4
Calculate the reactance for this:

1. Multiply the number of 6.28 for the frequency of the current and the inductance, the result will be the inductive reactance XL=6,28•f•L.
2. The number 1 divide by 6.28, the frequency of the current in the network and the capacitance of the device, the result is a capacitive resistance XC=1/(6,28•f•C).
3. Find the reactance of the folding of the results obtained in PP.1 and 2.
4. Find the reactive power by dividing the square of the voltage on the reactance RR=U2/Rp.
Thus, the reactive power depends on the frequency of the current in the network, inductance and capacitance in the load.
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