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Mechanical energy and its types

Source: licencja: CC 0.

Energia mechaniczna i jej rodzaje

You will learn
  • to develop your language skills in talking about mechanical, kinetic and potential energy in English,

  • English vocabulary related to the mechanical, kinetic and potential energypotential energypotential energy.

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Pokaz multimedialny - kręgle i katapulta. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).
Transformation of mechanical energy
Source: GroMar, licencja: CC BY 3.0.

On the basis of the presented slides the following conclusions can be drawn:

  1. To accelerate the ball while bowling, it is necessary to do work.

  2. A speeding ball also does work while turning over bowling pins.

  3. To bend an elastic metal strip, work should be done.

  4. An elastic metal strip also does work while returning to its original shape and gives the kinetic energy to the plasticine ball.

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nagranie abstraktu

The above situations can be described more precisely by introducing the notion of energyenergyenergy.

Definition of energy
Definition: Definition of energy
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nagranie abstraktu

EnergyenergyEnergy – scalar physical quantity which characterizes the state of the physical system as its ability to do work.

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nagranie abstraktu

EnergyenergyEnergy occurs in various forms, e.g. kinetic energykinetic energykinetic energy, elastic energy, thermal energy, nuclear energy.

EnergyenergyEnergy can only change its form, but it cannot be created or destroyed (the principle of energy conservationenergy conservationenergy conservation), for example: „energyenergyenergy production” in a coal‑fired power plant only means the transformation of chemical energy into electricity.

Work is one of the ways of converting the energyenergyenergy of one type into another. One of the most important formulas in physics is the relationship between work and the change of energyenergyenergy.

W=ΔE

The work done always equals the change of the energyenergyenergy of the system.

Definition of kinetic energy
Definition: Definition of kinetic energy
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nagranie abstraktu

The kinetic energykinetic energykinetic energy of the body is connected with motion; however, the body with the mass m has certain velocity v.

Ek=mv22
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nagranie abstraktu

An accelerating passenger car certainly has kinetic energykinetic energykinetic energy. A large truck moving at a slightly lower speed can have even greater kinetic energykinetic energykinetic energy because its weight is much greater than the weight of the passenger car.

Definition of potential (gravitational) energy
Definition: Definition of potential (gravitational) energy
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nagranie abstraktu

Potential energypotential energyPotential energy is related to the gravitational connection between the body with mass m and the Earth. This energyenergyenergy depends on the height on which the body is located. It is expressed by the following formula:

Ep=m·g·h

Constant g is called gravitational acceleration (acceleration of freefall) and its value for the Earth is:

g=9,81ms2
Definition of mechanical energy
Definition: Definition of mechanical energy
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nagranie abstraktu

The sum of the kinetic energykinetic energykinetic energy and the potential energypotential energypotential energy of a body is called mechanical energymechanical energymechanical energy.

Em=Ek+Ep
Task 1
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nagranie abstraktu

Calculate the kinetic energykinetic energykinetic energy of a bullet with the mass of 10 g moving at the speed of 800 ms. Compare this energyenergyenergy with the kinetic energykinetic energykinetic energy of a running boy whose mass is 50 kg and who is moving at the speed of 8 ms.

Task 2
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nagranie abstraktu

Calculate the change in the potential energypotential energypotential energy of a 0,5 kg book lifted from the floor to a shelf placed on the height of 2 m. What is the smallest possible work that must be done?

Task 3
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nagranie abstraktu

The car whose mass is 1000 kg was moving at the speed of 72 kmh and hit the roadside tree. From what altitude should this car fall down to hit the Earth with the same kinetic energykinetic energykinetic energy? Write appropriate conclusions about the consequences of such collision.

Exercises

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Exercise 1
Wersja alternatywna ćwiczenia: Decide which sentences are true. Możliwe odpowiedzi: 1. A plane which is flying at a certain altitude does not only have kinetic energy., 2. While falling down the body reduces its potential energy but increases the kinetic one., 3. While falling down the body retains its mechanical energy., 4. A plane which is flying at a certain altitude has only kinetic energy., 5. A plane which is flying at a certain altitude has only potential energy., 6. While braking suddenly, the energy of the car is lost forever.
zadanie
Source: GroMar, licencja: CC BY 3.0.
Exercise 2

Calculate the greatest altitude from which a 10 kg body is falling down if it has a kinetic energy of 60 J and a potential energy of 40 J. Calculate the value of the velocity which the body can hit the Earth.

Exercise 3

Calculate the power which you obtain while running up to the second floor. Write about the necessary equipment, write all necessary formulas and describe your activities.

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Exercise 4
Wersja alternatywna ćwiczenia: Indicate which pairs of expressions or words are translated correctly. Możliwe odpowiedzi: 1. energia - energy, 2. energia kinetyczna - kinetic energy, 3. energia potencjalna - potential energy, 4. energia mechaniczna - energy conservation, 5. zachowanie energii - mechanical energy
zadanie
Source: GroMar, licencja: CC BY 3.0.
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Interaktywna gra, polegająca na łączeniu wyrazów w pary w ciągu jednej minuty. Czas zaczyna upływać wraz z rozpoczęciem gry. Jeden ruch to odkrywanie najpierw jednej potem drugiej karty z wyrazem. Każdy wyraz jest odczytywany. Kolejny ruch to odkrywanie trzeciej i czwartej karty. W ten sposób odsłuchasz wszystkie wyrazy. Nawigacja z poziomu klawiatury za pomocą strzałek, odsłuchiwanie wyrazów enterem lub spacją. Znajdź wszystkie pary wyrazów.
Source: Zespół autorski Politechniki Łódzkiej, licencja: CC BY 3.0.

Glossary

energy
energy

energia

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wymowa w języku angielskim: energy
energy conservation
energy conservation

zachowanie energii

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wymowa w języku angielskim: energy conservation
kinetic energy
kinetic energy

energia kinetyczna

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wymowa w języku angielskim: kinetic energy
mechanical energy
mechanical energy

energia mechaniczna

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wymowa w języku angielskim: mechanical energy
potential energy
potential energy

energia potencjalna

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wymowa w języku angielskim: potential energy

Keywords

energyenergyenergy

energy conservationenergy conservationenergy conservation

kinetic energykinetic energykinetic energy

mechanical energymechanical energymechanical energy

potential energypotential energypotential energy