Newton meter reading and buoyancy against how far the object is lowered. The buoyancy grows while more of
the object goes under, then stays constant once it is fully submerged. A floating object makes the reading drop to zero.
#
object
liquid
W / N
reading / N
Fb / N
displaced / g
its weight / N
How to use this simulation
Choose the object (a cylinder 4.0 cm across), its volume and the liquid in the eureka can.
Set each value with ▼ and ▲ (hold to go faster; the ↑ ↓ keys or the mouse wheel in the box also work, Shift = ×10), or type a value in the box. ↺ puts it back to its start value. Outside the classroom range the box turns amber ⚠: fine to explore, but the lab can't do this.
Move the pointer over any graph (or tap it): a dashed line shows the values where it cuts each curve, or the values of the nearest data point.
Lower it with d (▲ ▼; how far the bottom of the object is below the surface). Read the newton meter. The liquid it
pushes out runs into the beaker on the balance.
Press ● Record to save weight, reading and displaced liquid. ✋ Let go releases the object: does it sink, float or hover?
The physics
Archimedes' principle: the upward buoyancy force equals the weight of the fluid displaced.
Fb = ρfluidVsubg, where Vsub is the volume under the surface.
Newton meter: T = W − Fb (the "apparent weight").
Floating: Fb = W ⇒ fraction under the surface = ρobject / ρfluid.
Sinks if ρobject > ρfluid, floats if less, hovers if equal.
After ✋ Let go the motion is shown in slow motion (×⅕), with water drag slowing it. Model: the eureka can starts full to the spout, so every cm³ the object pushes under the surface overflows into the
beaker. "Station 4 metal cylinder" reproduces the Station 4 sample: 2.50 N in air, 1.88 N in water.
Newton's laws
The badge above the scene says which law applies at this moment: 1st law — at rest or moving at a constant velocity, the resultant force is zero (ΣF = 0); 2nd law — accelerating, ΣF = ma. The table under the free-body diagram adds up the forces (ΣF) and compares them with m a (▾ folds it). Tick 3rd-law pairs to see every force with its partner: the same size and type, in the opposite direction, acting on the other body (the Earth, the floor, the string, the fluid…).