Mechanics & Simple Machines · GCSE Physics Topic 5
Atmospheric Pressure & Torricelli Barometer Simulator
Key exam takeaway: The vertical mercury height remains strictly 760mm regardless of tilt, lift, or diameter. Puncturing the top drops the column immediately.
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- Live Derivation
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3D Simulation Stage● 60 FPS
Parameter Controls
kPa
°
cm
Live Derivations & Metrics
Vertical Height h
--
Slanted Column Length L
--
Top Vacuum State
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Piston Water Lift Limit
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: In a Torricelli experiment tilted at 30°, how do vertical height and column length change?
Step-by-Step Derivation:
- Vertical height is determined by atmospheric pressure and remains 760mm; column length increases to 760/cos(30°) ≈ 877.6mm.
Worked Problem
Problem: If water replaced mercury in Torricelli experiment, how tall is the water column? Can a piston pump lift water 15m?
Step-by-Step Derivation:
- Water column h = p/(ρg) = 1.013*10^5 / (1000*9.8) ≈ 10.33m. Piston pumps rely on atmospheric pressure and cannot exceed 10.33m.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: If a bubble of air leaks into the top Torricellian space, does the measured pressure read high or low?
Answer Key: Reads low! Trapped air exerts downward pressure p_air, so mercury column ρgh = p0 - p_air < p0.
Q2. Variant 2: Carrying a Torricelli barometer to a mountain peak, how does the mercury column change?
Answer Key: It drops lower. Air density decreases with altitude, lowering atmospheric pressure and supported mercury height.
Q3. Variant 3: What force pulls apart two 30cm diameter evacuated Magdeburg hemispheres? (p=10^5 Pa)
Answer Key: Effective cross-section area S = πr² = 0.0707 m². Pull force F = p*S = 10^5 * 0.0707 ≈ 7070N.
Frequently Asked Questions & Misconceptions
Why doesn't mercury fountain out when the tube top is pierced?
Liquids fountain only if internal pressure exceeds external pressure. The top is a vacuum (0 Pa). Piercing lets 101 kPa air rush in, letting gravity drop the mercury.
Does using a wider glass tube change mercury height?
No! Hydrostatic pressure p = ρgh depends solely on density ρ and vertical height h, independent of cross-sectional area.
Does slightly lifting the tube change the mercury elevation difference?
No! The vertical elevation difference between column top and basin level remains 760mm. The top vacuum space expands.
Can astronauts drink with straws in space?
Inside a pressurized space station, yes; in the vacuum of outer space, no, because there is no atmospheric pressure to push liquid up.