QiLing Tools

⚖️Density Lab - Balance, Measuring Cylinder, Displacement, Error Analysis

A virtual lab for the mass and density chapter of middle-school physics. Level an unbalanced beam balance, put the object on the left, add weights with tweezers and slide the rider to read the mass. Drag the eye up and down beside a measuring cylinder to see why looking down reads high. The method pages draw the displacement, remainder, pin, sinker and overflow-can methods step by step, and an error-analysis quiz asks whether each mistake makes the density too big or too small.

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How to use Density Lab

  1. 1On Balance, follow the hints: level with the nuts, place the object, add weights, slide the rider and read the mass
  2. 2On Measuring cylinder, drag the eye to compare eye level, looking down and looking up
  3. 3On Measure density, pick a method and step through the procedure and the calculation
  4. 4Practise with Error analysis and Practice; wrong answers show the reason and the working

FAQ

The pointer leans left while levelling. Which way do I turn the nut?
Turn the balance nut to the right. A pointer to the left means the left side is heavier. Zero the rider before levelling, and never touch the nuts once you have started weighing - use weights and the rider instead.
Can I still get the mass if the object and weights were swapped?
Yes. At balance, left pan = right pan + rider reading. With the weights on the left, the object mass = total weights - rider reading.
Why use the remainder method for a liquid?
If you weigh an empty beaker, then beaker plus liquid, then pour everything into the cylinder, some liquid stays on the beaker wall, so the volume is too small and the density too big. The remainder method uses only the mass poured out, m1 - m2, and its volume, so leftovers do not matter.
Why does looking down at a measuring cylinder read too high?
Read with your eye level with the bottom of the meniscus. Looking down, the sight line through the meniscus bottom meets the scale on the near wall higher up, so the reading is too high; looking up gives a low reading. When measuring out a set volume it is reversed: looking down gives too little liquid.
What happens if I measure the volume before the mass?
The stone comes out of the cylinder wet, so its measured mass is too big and the density comes out too big. Measure the mass first, then the volume.

Features

  • A working beam balance: balance nuts, weight box, draggable rider and a pointer that follows the imbalance
  • Catches common mistakes: rider not zeroed, weighing before levelling, touching the nuts mid-weighing, swapped pans
  • Read and measure-out modes for the cylinder, with sight-line geometry showing the parallax error
  • Six density methods drawn step by step, with the material guessed from a density table
  • 14 error-analysis questions and least-squares m-V lines through the origin
  • Eight types of random calculation questions; density accepted in g/cm³ or kg/m³