🔍 Key Concepts

• How a U-tube manometer measures pressure as the difference in height between the two liquid columns • How to decide if the pressure is positive or negative by seeing which leg (the one connected to pressure or the one open to atmosphere) has the lower liquid level • Remember that the reading is in inches of water (in. H₂O), not from one surface to the bottom but surface to surface

💭 Think About

• Look at the exact water levels on both sides: by how many inches are they different on the scale? • If the side connected to the pressure source is pushed down compared with the atmospheric side, does that mean the applied pressure is greater or less than atmospheric? • Imagine the tube with no pressure difference (both sides at atmospheric). Where would the levels be, and how would they shift when you apply a higher or lower pressure on the left side?

✅ Before You Answer

• Measure the vertical distance between the two liquid surfaces using the ruler, not the distance from the bottom of the U • Determine which side is connected to the pressure source and which side is open to atmosphere • Decide the sign: if the pressure side’s liquid level is lower, the pressure is above atmospheric (positive); if it is higher, the pressure is below atmospheric (negative)