How Do You Measure the Density of a Rubber Eraser?

What steps would you take to determine the density of a rubber eraser?

Use a balance for mass and a graduated cylinder for volume. Density is mass divided by volume, written as rho = M/V, according to NASA Goddard Institute for Space Studies. That is the whole job: get two defensible measurements, then do one division.

1. Measure mass. Place the dry eraser on the balance and record its mass in grams.
2. Set a starting volume. Add enough water to a graduated cylinder that the eraser can be completely submerged. Record the initial volume at the center of the bottom of the concave meniscus.
3. Submerge without drama. Gently lower the eraser below the surface. Do not drop it in; splashing loses water and changes the number you need.
4. Record the final volume. Wait for the water to come to rest, check for bubbles, then read the meniscus again.
5. Calculate volume and density. Subtract initial volume from final volume. Divide the mass by that difference.

Use this data layout. It keeps the calculation visible instead of burying it in a line of notes.

For a check on the arithmetic, the Maine Geological Survey gives a specimen example of 42 g displacing 11.6 mL, which produces about 3.62 g/mL. That is not a target result for an eraser; it is a clean model for the calculation. NASA lists rubber at about 1.10 to 1.19 g/cm3 as an approximate comparison range, so a result far outside that range is a reason to inspect the procedure before declaring the eraser unusual.

How do you find the volume of an eraser if it is not a perfect shape?

Find an irregular eraser’s volume by measuring the water it displaces when it is fully submerged. You do not need to force a lumpy or worn eraser into a length-times-width-times-height formula; the water-level change does the volume measurement directly.

The Florida State University Department of Chemistry and Biochemistry explains that the displaced-water volume of a fully submerged object equals the object’s volume. If the cylinder rises from one marked level to another, subtract the first reading from the second. NOAA Ocean Explorer adds the useful unit shortcut: 1 mL equals 1 cm3, so the result can go straight into a density calculation with grams.

Run the two-reading rule: record the water level before the eraser enters, then record it after the eraser is fully under. Do not use the final reading alone. The difference is the measurement that carries the decision.

Read the meniscus consistently. Water forms a concave curve, and FSU directs students to read the center of the curve’s bottom. For a cylinder marked in 1 mL increments, estimate one additional digit and record to the nearest 0.1 mL. That small discipline reduces cognitive load when you compare repeated trials, much like checking every input before you verify a Toyota deal by comparing the out-the-door total.

Why does the water level rise when an object is put in a graduated cylinder?

The water level rises because a submerged object takes up space and pushes aside its own volume of water. That is why displacement works: the increase in the cylinder is the object volume, provided the object is completely submerged and no water is lost.

NOAA Ocean Explorer connects this observation to Archimedes’ principle: an object in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid. The practical version is simpler. An eraser that sinks displaces its full volume on its own; an object that floats must be held under water before you take the final reading.

Use the quiet-cylinder check before writing the final number: water settled, object fully submerged, no bubbles clinging to it, and no splash marks suggesting lost water. Truman State University specifically directs students to gently tap the cylinder to dislodge attached air bubbles. A bubble adds apparent volume. Your division then produces a density that looks precise but is wrong.

If the object dissolves in water or absorbs it, this water-displacement method is a poor fit because its mass or shape can change during the test. The provided sources do not give a substitute method for those materials. State that limitation in a lab report rather than presenting an unstable result as a clean measurement.