Presentation on the topic of efficiency. simple mechanisms. Efficiency of simple mechanisms Preparation for GIA. Inclined plane is useless

circuit diagram heat engine

Heater T1

Refrigerator T2

working body

problem

use of TD

• argument
• example

disadvantageous

TOPIC OF THE LESSON

"Efficiency

thermal engines"

Lesson objectives:

Task number 1.

What is a heater?

transmitted by the heater?

Task number 1.

Determine the efficiency of the tractor engine, which required 1.2 kg of fuel with a specific heat of combustion of 42 MJ to perform work of 15 MJ.

To solve this problem, you need to answer the following questions:

What is useful work?

What is a heater?

What thermal processes take place in the heater?

transmitted by the heater?

Which of the three efficiency formulas is better to use in this

Q: What does "Tractor engine efficiency is 30%" mean?

• In the internal combustion engine, 0.5 kg of fuel was consumed, the calorific value of which was 46 106 J/kg, while the engine performed 7 106 J of useful work. What is its efficiency?
• In a heat engine, 300 J of work is done due to each kilojoule of energy received from the heater. Determine the efficiency of the machine.
• The useful power of the aircraft engines is 2300 kW. What is the efficiency of engines if, at an average speed of 250 km / h, they consume 288 kg of kerosene per 100 km of track?

Efficiency of modern serial gas turbine engines

for different power classes

• Can the efficiency be equal to or greater than 100%?
• How can efficiency be increased?
• Will an increase in Qn lead to an increase in useful work? To increase efficiency?
• Will a decrease in Qx lead to an increase in useful work? To increase efficiency?
• What is more profitable: to increase Qn or to decrease Qx? (Mathematical analysis is carried out - it is more convenient to do this on the last efficiency formula)
• What is technically easier (more possible): to increase Qн or to decrease Qх? What are these problems related to?

QUESTIONS

WAYS TO CHANGE EFFECTIVENESS (warm-up)

• HIGH QUALITY FUEL APPLICATION
• LACK OF LUBRICATION IN THE WORKING PARTS OF THE MECHANISMS
• REDUCTION OF HEAT TRANSFER THROUGH CYLINDER WALLS
• REDUCING THE “REFRIGERATOR” TEMPERATURE
• IMPROVE CASE TIGHTNESS
• PREVENTION OF LEAKAGE OF GASOLINE VAPOR FROM THE FUEL TANK BY ADSORPTION AND SUCTION OF VAPOR INTO THE INTAKE SYSTEM.

Pick up a proverb

What helps improving the quality of education	What hinders improving the quality of education

Task for self-study: learn the theoretical part according to the abstract in the notebook, problem book A.P. Rymkevich No. 679, task No. 2

“The heat engine receives 100 J from the heater for a cycle of work and gives 40 J to the refrigerator. What is the efficiency of the heat engine?”

Optional: evaluate the efficiency of a marine diesel engine (see below)

simple mechanisms. Efficiency of simple mechanisms

1. The lever is in balance under
by the action of two forces, if the moment
force that rotates it clockwise
arrow, ... moment of force rotating
it counterclockwise.
A. is directly proportional.
B. is inversely proportional.
C. is equal.

2. Movable block...
A. gives a gain in strength of 2 times.
B. does not give a gain in strength.
C. gives a gain in strength of 4 times.

3. Using the lever, the worker raises
load weighing 200 kg. What strength does he
applies to the larger shoulder
lever 2 m long, if less
shoulder is 0.5 m?
A. 200 N.
B. 400 N.
C. 500 N.

A.
b.
C.
4. How much weight can be lifted with
using a movable block, applying
force 200 N?
200 N.
400 N.
100 N.

A.
b.
C.
5. Applying a force F = 100 N, a load of mass
m lifted with a movable
block to a height h = 3 m.
distance stretched end of rope
(rice.)?
3m.
6 m
1.5 m

A.
b.
C.
6. Determine what the mass m is
lifted load (Fig. 3).
40 kg.
20 kg.
80 kg.

A.
b.
C.
7. Load weighing 1000 N with a lever
raised to height h. Define the job
perfect force F = 200 N, h = 20 cm
(rice.).
400 J
250 J
200 J

8. Compare
gravity work with work
applied force F (Fig. 2).
A.
b.
C.
The work of gravity
more
work
attached
strength:
loss at work.
The work of gravity
less
work
attached
strength:
gain at work.
The work of gravity
is equal to
work
attached
strength:
no gain, no
loss at work.

A.
b.
9. Coefficient of useful
action is called attitude...
Work to... work.
useful; complete.
complete; useful.

A.
b.
10. In practice perfect with
using mechanism complete work
always... useful work.
less.
more.

slide 2

1. Does a simple mechanism give a gain in work? Justify the answer. 2. The content of the "Golden Rule" of mechanics. 3. What is the relationship between the paths traveled by the points of application of forces on the lever and these forces? 4. What are simple mechanisms used for? 5. What do they lose when using a lever that gives a gain in strength? Repetition:

slide 3

6. How many times do they lose on the way, using a movable block to lift loads. 7. Specify formulas for calculation: Power A = F*S Work V = S / t Speed ​​P = F / S Density p = m / v Pressure N = A / t

slide 4

Plan for the study of the topic: "Efficiency of mechanisms."

1. For what simple mechanisms are used. 2. The concept of useful work and complete work and their comparison. 3. The concept of the efficiency of the mechanism, its comparison with 100%. 4. Ways to improve efficiency.

slide 5

Simple mechanisms are used to…

slide 6

The concept of useful work and complete. Apples for processing into juice, the loader pours out of the baskets into the back of the car. The full job is loading apples. It consists of lifting the apples themselves and lifting the baskets. The work of lifting the apples themselves is useful, but that of lifting the baskets is useless, because they must be lowered or thrown down.

Slide 7

Lifting work using an inclined plane, height h and length ℓ.

F Useful work A n = F *h = m *q *h But at the same time we overcome the friction force, the force of gravity of other devices, we do additional work. The work expended is greater than the useful work Az > A n. Useful work is only a part of the total work.

Slide 8

The characteristic of the mechanism, which determines what proportion of useful work is from the total, is called efficiency.

A p Az 100% Can the efficiency be 100%, > 100%? Justify the answer. How to increase efficiency? Reduce the mass of moving parts, reduce friction in parts. efficiency =

Slide 9

Solving problems for calculating efficiency.

Determine the efficiency of devices and mechanisms in the following situations: 1. A barrel is rolled on an inclined platform, applying a force of 240N. Barrel weight 100kg, platform length 5m, platform height 1m. 2. A bucket of sand weighing 200N is lifted with a fixed block to a height of 10m, acting on a rope with a force of 250N.

View all slides

Objectives: educational: to form the skills of experimental determination of efficiency and gain in the force of an inclined plane; to consolidate the skills of measuring forces using a dynamometer; educational: the formation of communication skills of working in a team (mutual respect, mutual assistance and support). developing: to develop the thinking and practical skills of students. Equipment: laboratory: wooden ruler, wooden block, dynamometer, tripod; projector, screen, laptop.

View document content
“Presentation for the lesson “Measuring the efficiency of an inclined plane”. 7th grade."

From ancient times

To facilitate his work, a person uses various mechanisms.

(Greek "mekhane" - machine, tool)

Simple mechanism- inclined plane.

Instead of lifting a heavy load to a certain height,

it is rolled in or dragged to the same height along an inclined plane.

It is always easier to use a gentle slope than a steep one.

The gain in strength does not arise "for nothing": you have to roll in barrels

along a longer path.

The inclined plane is indispensable!

The inclined plane is useless!

Our task:

build an inclined plane;

Mechanical work: A = Fs

useful work is the work required to lift a body to a height 𝗵.

The work is done by a force directed upwards and equal in absolute value to the force of gravity.

Work expended is work done on an inclined plane.

The work is done by the force with which we pull the body up along the inclined plane - Fthrust.

The path traveled by the body is the length of the inclined plane 𝓵 :

Efficiency factor (COP):

𝝶 = · 100 %

Power gain k:

𝗸 =

How do we measure gravity?

How do we measure traction force?

∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣ ∣∣∣∣ ∣

Value of division:

C. d. = = 0.1

𝓵 , m

𝓵 , m

𝝶 , %

𝝶 , %

1 row: h = 7 cm

2nd row: 𝗵 = 10 cm

3rd row: 𝗵 = 15 cm

We conclude (general):

-about efficiency dependencies inclined plane

from the angle of its inclination;

- on the dependence of the gain in the strength of the inclined plane on the angle of its inclination.

slide 1

The efficiency of the mechanism. At home: §61

Repeat " Golden Rule» mechanics. To get acquainted with the concept of efficiency as the main characteristic of the working mechanism.

The purpose of the lesson:

slide 2

1. Does a simple mechanism give a gain in work? Justify the answer. 2. The content of the "Golden Rule" of mechanics. 3. What is the relationship between the paths traveled by the points of application of forces on the lever and these forces? 4. What are simple mechanisms used for? 5. What do they lose when using a lever that gives a gain in strength?

Repetition:

slide 3

6. How many times do they lose on the way, using a movable block to lift loads. 7. Specify formulas for calculation: Power A = F*S Work V = S / t Speed ​​P = F / S Density p = m / v Pressure N = A / t

slide 4

Plan for the study of the topic: "Efficiency of mechanisms."

1. For what simple mechanisms are used. 2. The concept of useful work and complete work and their comparison. 3. The concept of the efficiency of the mechanism, its comparison with 100%. 4. Ways to improve efficiency.

slide 5

Simple mechanisms are used to…

slide 6

The concept of useful work and complete.

Apples for processing into juice, the loader pours out of the baskets into the back of the car.

The full job is loading apples.

It consists of lifting the apples themselves and lifting the baskets.

The work of lifting the apples themselves is useful, but that of lifting the baskets is useless, because they must be lowered or thrown down.

Slide 7

Lifting work using an inclined plane, height h and length ℓ.

Useful work A p \u003d F * h \u003d m * q * h

But at the same time we overcome the force of friction, the force of gravity of other devices, we do additional work.

The work expended is greater than the useful work Az > A p.

Useful work is only a part of a complete work.

Slide 8

The characteristic of the mechanism, which determines what proportion of useful work is from the total, is called efficiency.

Can efficiency be 100%, > 100%? Justify the answer.

How to increase efficiency?

Reduce the mass of moving parts, reduce friction in parts.

Slide 9

Solving problems for calculating efficiency.

Determine the efficiency of devices and mechanisms in the following situations: 1. A barrel is rolled on an inclined platform, applying a force of 240N. Barrel weight 100kg, platform length 5m, platform height 1m. 2. A bucket of sand weighing 200N is lifted with a fixed block to a height of 10m, acting on a rope with a force of 250N.