Key relationship
vjet=√(2gh); horizontal range=2√(hH); Δp=½ρair(vupper²−vlower²); Flift=ΔpA.
Physics · Class 11
Drain a tank and compare lift pressure
Mechanical Properties of Fluids
A liquid head becomes jet kinetic energy, giving an exit speed proportional to the square root of head. In the separate air example, faster flow above than below gives lower pressure above and a net upward pressure force.
Open the interactive experiment →Drain a tank and compare lift pressure
திரவ உயரத்தின் நிலை ஆற்றல் பாய்ச்சலின் இயக்க ஆற்றலாக மாறும். மேற்புறக் காற்று வேகம் அதிகமானால் அங்கு அழுத்தம் குறைந்து தூக்கு விசை ஏற்படும்.
Key notes, relationships and model limits
Remember
A liquid head becomes jet kinetic energy, giving an exit speed proportional to the square root of head. In the separate air example, faster flow above than below gives lower pressure above and a net upward pressure force.
Common trap
A real wing’s lift requires solving its flow and circulation; equal transit-time reasoning is not used.
Model limits
Large tank with small horizontal outlet and fixed head. Separately, imposed steady inviscid air speeds at equal height give a Bernoulli pressure difference (ρair=1.225 kg/m³); this is not a full real-wing flow model.
What you will learn
Relate head to jet speed and imposed airflow differences to dynamic lift.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
At h=2 m, jet speed=6.264 m/s and range from 1 m height is 2.828 m. Air speeds 20 m/s above and 10 m/s below give Δp=183.75 Pa and lift 183.75 N on 1 m².
Why this matters
The model connects drain a tank and compare lift pressure with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
If liquid head becomes four times larger, what happens to exit speed?
- It becomes four times larger
- It doubles
- It stays unchanged
Read the explanation
The exit speed is proportional to √h.
Course connection: Class XI Chapter 9. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.