Twenty minutes or less.

Week 8 carries three live assessments: the tutorial portfolio item, the Mastering Physics modules, and — distinctively this week — an assessed Lab/Practical worksheet that feeds the 10% Lab Report. Plan to be at the lab session. Bring the worksheet.

5-minute version

Three pillars. One sentence each.

• Fluid properties — density, specific weight, specific gravity, and Newton’s law of viscosity $\tau =\mu du/dy$.
• Hydrostatic pressure — $\Delta p=\rho g\Delta h$ + Pascal’s law isotropy. Walk manometer paths: down adds, up subtracts.
• Buoyancy — $F_B={\rho }_{\text{fluid}}g{V}_{\text{displaced}}$. Always use the fluid’s density and the displaced volume.

Open the cheatsheet quiz, do 3 easy questions, close it. You’re prepped enough for the tutorial.

20-minute prep plan

Time	Action
0–5 min	Skim the cheatsheet tables.
5–10 min	Re-do Tutorial Ex 4 (oil-over-water gauge pressures) by hand.
10–15 min	Take the cheatsheet quiz. Don’t worry about the score.
15–20 min	Read “Common mistakes” + the exam-style sample in the in-depth note.

Lab-specific prep

The Lab/Practical class this week is assessed — your data + worksheet feed the 10% Lab Report. Before you walk in:

• Re-read the lab brief / worksheet (check LMS for the document).
• Be confident with $\rho =m/V$, $F_B=\rho gV$, and how to convert a measured submerged length / mass to a density.
• Know the difference between gauge and absolute pressure — instruments usually read gauge.
• Bring a calculator, a pen, the worksheet, and (if relevant to your lab) the data table from your prep.

In the session itself:

• Record numbers as you measure them — don’t trust memory.
• Note units beside every measurement.
• Sanity-check each result before moving on (does the buoyant force roughly equal the weight of displaced fluid?).
• Submit the worksheet at the end. This is the assessment artefact — don’t leave with it.

What to revise first

Most students slip on these in Week 8 problems:

1. Forgetting the “displaced” in $F_B$. Use ${\rho }_{\text{fluid}}$, not ${\rho }_{\text{object}}$. For a floating body, $V$ is the submerged part only.
2. Sign errors in manometer walks. Going down through a fluid adds $\rho g\Delta h$; going up subtracts. Pick a direction at the start and commit.
3. Treating $SG$ as a density. $SG=13.55$ means $\rho =13550kg/{\mathrm{m}}^3$. Convert first, plug second.
4. Inclined manometer geometry. The inclined length is not the vertical drop; multiply by $\sin \theta$ first.

Key formulas

$$\rho =\frac{m}{V},\gamma =\rho g,SG=\frac{\rho }{{\rho }_{\text{water}}}$$ $$\tau =\mu \frac{du}{dy}\stackrel{\text{integrate}}{\to }{V}_{\text{shear}}=\tau A$$ $$\Delta p=\rho g\Delta h\stackrel{\text{walk path}}{\to }\text{pressure at any point}$$ $$F_B={\rho }_{\text{fluid}}g{V}_{\text{displaced}}$$

Likely workshop tasks

Task type	What the setup usually looks like
Density / volume warm-up	Trapezoidal pool, irregular tank — compute $V$ then $m=\rho V$.
Viscosity bearing	Plate or concentric cylinders sliding through a thin oil film; find $\tau$, $V_{\text{drag}}$, $P$.
Manometer walk	Mixed-fluid path with mercury, oil, water; find pressure at a labelled point in gauge or absolute.
Buoyancy / Archimedes	Submerged block on a cable, floating iceberg, hydrometer calibration.
Pressure to height conversion	Express a given pressure as a column of mercury, water, or named fluid.

Mistakes to avoid

• Mixing $g=9.8$ and $g=9.81$ within a single problem.
• Treating gauge pressure as absolute (or vice versa) without converting via $p_{\text{abs}}=p_{\text{atm}}+p_{\text{gauge}}$.
• Including the air-column $\rho gh$ when it’s a few Pa and the rest of the path is kPa.
• Using object density in the buoyancy formula.
• In hydrometer / floating-body questions, using total volume instead of submerged volume.
• Skipping the unit check on the final answer.

Mini self-test

Try these without notes. Ten minutes total.

1. A fluid has $\rho =850kg/{\mathrm{m}}^3$. Compute $\gamma$ and $SG$.
2. A horizontal plate area $0.4{\mathrm{m}}^2$ slides at $0.1m/s$ over a stationary surface separated by a $2\mathrm{mm}$ oil film ($\mu =0.1\mathrm{Pa}\cdot \mathrm{s}$). Find the drag force.
3. A U-tube manometer connects two air containers. Mercury column height difference $0.20\mathrm{m}$. What is $|\Delta p|$?
4. A $0.05{\mathrm{m}}^3$ wooden block ($\rho =600kg/{\mathrm{m}}^3$) floats in fresh water. What fraction of its volume is submerged?

Answers:

Question	Answer
1	$\gamma =8330N/{\mathrm{m}}^3$; $SG=0.85$
2	$\tau =\mu \Delta u/\Delta y=0.1\times (0.1/0.002)=5\mathrm{Pa}$; $V=5\times 0.4=2.0\mathrm{N}$
3	$
4	Submerged fraction $=600/1000=60\%$

Done checklist

• Read the cheatsheet tables.
• Tutorial Ex 4 worked by hand.
• Cheatsheet quiz attempted.
• Mini self-test attempted.
• Lab brief / worksheet re-read; calculator, pen, worksheet ready for the lab session.

That’s it. Close the laptop.

Source files used

• EGD102-Physics/Lecture8_CTP1.pdf
• EGD102-Physics/EGD102 - Lecture8 - Notes.pdf
• EGD102-Physics/Tutorial 8.pdf
• EGD102-Physics/Tutorial 8_Solutions.pdf