What is the Principle of a Jet Engine?

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Grade Level:

Class 7

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

The principle of a jet engine is based on Newton's Third Law of Motion, which states that 'for every action, there is an equal and opposite reaction'. A jet engine works by taking in air, compressing it, mixing it with fuel and burning it, then pushing out hot gases at high speed to create forward thrust.

Simple Example

Quick Example

Imagine you're standing on a skateboard and you throw a heavy cricket ball forward with all your might. What happens? You move backward! The action is throwing the ball forward, and the equal and opposite reaction is you moving backward. A jet engine does something similar but with hot gas instead of a ball.

Worked Example

Step-by-Step

Let's understand how a jet engine applies Newton's Third Law:

Step 1: Air Intake – A fan at the front of the engine sucks in a large amount of air from the atmosphere, just like a big vacuum cleaner.
---Step 2: Compression – This air is then squeezed tightly by spinning blades called compressors, increasing its pressure and temperature.
---Step 3: Combustion – The compressed air is mixed with jet fuel and ignited in a combustion chamber. This creates very hot, high-pressure gases.
---Step 4: Expansion & Thrust – These hot gases rush backward through a turbine (which spins the compressor and fan) and then are forced out of the engine's nozzle at extremely high speed.
---Step 5: Reaction – The action is the engine pushing hot gases backward. The equal and opposite reaction is the engine, and thus the aeroplane, being pushed forward with great force (thrust).
---Answer: The jet engine generates thrust by expelling hot gases backward, causing a forward reaction force.

Why It Matters

Understanding jet engine principles is crucial for designing faster aeroplanes, rockets for space technology (like ISRO missions), and even advanced drones. Careers in aerospace engineering, aviation, and defence rely heavily on this knowledge, helping us travel faster and explore space.

Common Mistakes

MISTAKE: Thinking the engine pulls the plane forward. | CORRECTION: The engine pushes the plane forward by expelling gases backward, due to Newton's Third Law.

MISTAKE: Believing the engine uses air only for cooling. | CORRECTION: Air is primarily used as a working fluid – it's compressed, heated, and expelled to create thrust.

MISTAKE: Confusing jet engines with propeller engines. | CORRECTION: Jet engines create thrust by expelling hot gases, while propeller engines create thrust by pushing air with spinning blades.

Practice Questions

Try It Yourself

QUESTION: Which law of motion is the main principle behind a jet engine? | ANSWER: Newton's Third Law of Motion.

QUESTION: What is the 'action' in a jet engine that creates thrust? | ANSWER: The action is the engine pushing hot gases backward out of its nozzle.

QUESTION: If a jet engine expels 100 kg of gas backward every second, why does the plane move forward? Explain using the principle. | ANSWER: According to Newton's Third Law, if the engine exerts a force to push 100 kg of gas backward, the gas exerts an equal and opposite force, pushing the engine (and thus the plane) forward.

MCQ

Quick Quiz

What is the primary role of the hot gases expelled from a jet engine?

To cool down the engine parts

To provide light for night flying

To create a forward pushing force (thrust)

To make a loud sound

The Correct Answer Is:

The hot gases are expelled at high speed to create a strong backward action force, which results in an equal and opposite forward reaction force, known as thrust, propelling the aircraft.

Real World Connection

In the Real World

Whenever you see an aeroplane taking off from an airport like Delhi's IGI or Mumbai's Chhatrapati Shivaji, you are witnessing the principle of a jet engine in action. The powerful roar you hear is the sound of hot gases being pushed out, generating the immense thrust needed to lift the massive aircraft into the sky for your next vacation or business trip.

Key Vocabulary

Key Terms

THRUST: The forward pushing force that propels an aircraft or rocket | COMPRESSOR: A part of the jet engine that squeezes air, increasing its pressure | COMBUSTION CHAMBER: Where fuel is mixed with compressed air and burned to create hot gases | NEWTON'S THIRD LAW: For every action, there is an equal and opposite reaction | NOZZLE: The opening at the back of the engine where hot gases are expelled.

What's Next

What to Learn Next

Great job understanding how jet engines work! Next, you can explore 'How do rockets work?' You'll find that rockets use a very similar principle but carry their own oxygen, which is essential for space travel beyond Earth's atmosphere.