Topicmc0c3fde51d59498b_1528449000663_0Topic

Mechanical energy and its types

Levelmc0c3fde51d59498b_1528449084556_0Level

Second

Core curriculummc0c3fde51d59498b_1528449076687_0Core curriculum

III. Energy. The student:

1) uses the term of mechanical work together with its unit; uses in calculations the relationship between the work done and the force or the displacement with/on which it was done.

Timingmc0c3fde51d59498b_1528449068082_0Timing

45 minutes

General learning objectivesmc0c3fde51d59498b_1528449523725_0General learning objectives

Presenting the concept of energy and its relationship with work.

Key competencesmc0c3fde51d59498b_1528449552113_0Key competences

1. Defining the concept of energy.

2. Presenting different possibilities of changing the energy of one type into another one.

3. Defining mechanical energy as the sum of potential and kinetic energy.

Operational (detailed) goalsmc0c3fde51d59498b_1528450430307_0Operational (detailed) goals

The student:

- defining energy as a scalar physical quantity associated with work,

- presenting mechanical energy as the sum of potential and kinetic energy.

Methodsmc0c3fde51d59498b_1528449534267_0Methods

1. Talk and brainstorming.

2. Learning through the application of acquired rules and solving problem tasks.

Forms of workmc0c3fde51d59498b_1528449514617_0Forms of work

1. Individual cooperation between the student and the teacher.

2. Working in groups on solving problem tasks.

Lesson stages

Introductionmc0c3fde51d59498b_1528450127855_0Introduction

What does work mean?

Give examples of doing work in everyday life.

What do you need to do work?

Conclusion:

To do work you need: ... .

Proceduremc0c3fde51d59498b_1528446435040_0Procedure

[Slideshow]

On the basis of the presented slides the following conclusions can be drawn:mc0c3fde51d59498b_1527752263647_0On 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 kinetic energy to the kinetic ball.

The above situations can be described more precisely by introducing the notion of energy.mc0c3fde51d59498b_1527752256679_0The above situations can be described more precisely by introducing the notion of energy.

Definition of energy.

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

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

Energy can only change its form, but it cannot be created or destroyed (the principle of energy conservation), for example: „energy 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 energy of one type into another. One of the most important formulas in physics is the relationship between work and the change of energy:

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

Definition of kinetic energy.

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

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

Definition of potential (gravitational) energy.

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

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

Definition of mechanical energy.

The sum of the kinetic energy and the potential energy of a body is called mechanical energy:

Task 1

Calculate the kinetic energy of a bullet with the mass of 10 g moving at the speed of 800 $\frac{m}{s}$. Compare this energy with the kinetic energy of a running boy whose mass is 50 kg and who is moving at the speed of 8 $\frac{m}{s}$.

Task 2

Calculate the change in the potential 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

The car whose mass is 1000 kg was moving at the speed of 72 $\frac{km}{h}$ and hit the roadside tree. From what altitude should this car fall down to hit the Earth with the same kinetic energy? Write appropriate conclusions about the consequences of such collision.mc0c3fde51d59498b_1527712094602_0The car whose mass is 1000 kg was moving at the speed of 72 $\frac{km}{h}$ and hit the roadside tree. From what altitude should this car fall down to hit the Earth with the same kinetic energy? Write appropriate conclusions about the consequences of such collision.

Lesson summarymc0c3fde51d59498b_1528450119332_0Lesson summary

Energy is a scalar physical quantity which characterizes the state of the physical system as its ability to do work.

Energy can be neither destroyed nor created. It is possible, however, to convert one form of energy into another.

One way to convert energy is to do work.

Mechanical energy is the sum of the kinetic energy (related to motion) and the potential energy (associated with gravitational interactions).

Selected words and expressions used in the lesson plan

energyenergyenergy

energy conservationenergy conservationenergy conservation

kinetic energykinetic energykinetic energy

mechanical energymechanical energymechanical energy

potential energypotential energypotential energy