The Working of a Hot Air Balloon
IELTS Academic Writing Task 1 -Diagram (Illustration)

IELTS Writing Task 1 Question
The two diagrams describe the main parts of a hot air balloon and indicate how it works. Write a report for a university lecturer describing the information given below.

Common Questions for Data Summary
1. Graph Type: Diagram (Illustration)
2. Title: The Working of a Hot Air Balloon
3. What are the units of measurement? No specific units of measurement (illustration of mechanical processes)
4. Who: Passengers in the hot air balloon (controlling the ascent and descent)
5. When: Not specified (general working mechanism of a hot air balloon)
6. Where: Not specified (the hot air balloon is generally used worldwide)
7. Topic: Description of the parts and working of a hot air balloon
Comparison Showing and Trends Any change over time (such as an increase or a decrease) is a trend.
Comparison 1: Ascending Balloon
Details:
- The first diagram shows the balloon ascending. The gas cylinder tank at the bottom fuels the burners, which heat the air inside the balloon envelope, causing it to inflate. The passengers control the valve at the top by pulling the cord to regulate the balloon’s ascent.
Comparison 2: Descending Balloon
Details:
- In the second diagram, the balloon is descending. To lower the balloon, the burners are turned off, and the valve cord is pulled by the passengers to open the valve at the top, releasing hot air. This causes the balloon to deflate and descend.
Sample Answer
The given diagrams illustrate the operation of a hot air balloon and the mechanisms that allow it to ascend and descend.
Overall, the hot air balloon’s design allows the passengers to control its ascent and descent by regulating the burners and the valve.
In the first diagram, the hot air balloon is seen ascending. The gas cylinder at the base provides fuel to the burners, which heat the air inside the balloon’s envelope. As the heated air rises, it inflates the envelope, causing the balloon to lift. The passengers control the ascent by pulling the cord attached to the valve at the top of the envelope, which remains closed during the ascent.
The second diagram depicts the descending balloon. The burners are switched off to lower the balloon, and the passengers pull the valve cord to open the valve at the top. This releases the hot air from the envelope, causing it to deflate and the balloon to descend gradually.
Top 25 Vocabulary
Vocabulary | Meaning | Synonyms | Examples | Type |
Ascend |
To rise or go up |
Rise, climb |
The hot air balloon ascends when the burners are on. |
Verb |
Descend |
To move downward |
Fall, drop |
To make the balloon descend, the burners must be turned off. |
Verb |
Envelope |
The large fabric bag of a hot air balloon |
Balloon skin, covering |
The balloon envelope inflates as the air inside is heated. |
Noun |
Valve |
A device for controlling the flow of air or gas |
Regulator, control |
The valve is controlled by the passengers to regulate the balloon’s height. |
Noun |
Deflate |
To let out air or gas, causing something to shrink |
Shrink, collapse |
Pulling the valve cord deflates the balloon and causes it to descend. |
Verb |
Mechanism |
A system of parts working together to perform a function |
System, device |
“The mechanism of the balloon allows passengers to control ascent and descent.” |
Noun |
Control |
To manage or direct the operation of something |
Regulate, direct |
“Passengers control the balloon’s ascent by managing the burners.” |
Verb |
Fuel |
A substance that provides energy for a machine |
Energy source, propellant |
“The gas cylinder supplies fuel to the burners.” |
Noun |
Inflate |
To fill something with air or gas, making it expand |
Inflate, expand |
“The balloon inflates as the air inside becomes hot.” |
Verb |
Lift |
To raise or elevate something |
Raise, elevate |
“The heated air inside the balloon lifts it off the ground.” |
Verb |
Regulation |
The act of controlling or adjusting something |
Control, adjustment |
“Regulation of the burner ensures the balloon rises smoothly.” |
Noun |
Cylinder |
A cylindrical container used to hold a substance |
Tank, container |
“The gas cylinder at the base provides fuel for the burners.” |
Noun |
Cord |
A flexible string or rope used for control |
Rope, string |
“Passengers pull the cord to open the valve.” |
Noun |
Deflation |
The process of releasing air or gas to shrink something |
Shrinking, collapsing |
“Deflation occurs when the valve is opened and hot air escapes.” |
Noun |
Temperature |
The degree of heat present in a substance |
Heat, warmth |
“The heated air causes the balloon to rise.” |
Noun |
Descent |
The act of moving downward |
Drop, fall |
“The balloon’s descent is controlled by opening the valve.” |
Noun |
Envelope |
The fabric part of the balloon that holds the hot air |
Balloon skin, covering |
“The envelope inflates as the balloon ascends.” |
Noun |
Ascent |
The action of rising or going up |
Rise, climb |
“The ascent is controlled by adjusting the burners and valve.” |
Noun |
Adjust |
To make changes to achieve a desired result |
Modify, change |
“The passengers adjust the burners to control the balloon’s height.” |
Verb |
Buoyancy |
The ability of an object to float in a fluid |
Floating, lift |
“The balloon’s buoyancy is affected by the temperature of the air inside.” |
Noun |
Pressure |
The force exerted on a surface or object |
Force, tension |
“The pressure inside the balloon increases as the air heats up.” |
Noun |
Gradually |
In small steps or increments |
Slowly, progressively |
“The balloon descends gradually as air is released from the envelope.” |
Adverb |
Vent |
An opening that allows air or gas to escape |
Opening, outlet |
“The vent at the top of the balloon allows hot air to escape.” |
Noun |
Release |
To let something go or escape |
Free, discharge |
“Releasing the air from the balloon causes it to descend.” |
Verb |
Envelope |
A protective covering or container, especially for hot air in a balloon |
Cover, casing |
“The balloon’s envelope is made of heat-resistant material.” |
Noun |
Shortlisted | Selected from a larger group for further consideration | Selected, chosen | “The shortlisted candidates will proceed to the next stage.” | Verb/Adjective |

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