The Mystery of the Broken Straw

Look at the straw. Above the water it looks continuous, but where it crosses the surface the submerged
part looks shifted, almost as if there were two pieces. Is it broken, or is the light tricking us?

The remote lab uses a real laser, a transparent container of water and two views
of the same setup: from above and from the side. We won't peek at the answer ahead of
time: first choose what you think the beam will do when it enters the water at an angle.

In the three selectable cards in the question, the light area is the air, the blue area is the water and the dashed line
marks a reference direction: it crosses the surface at a right angle exactly where the beam enters.
The only thing that differs from card to card is the red path of the light.

You are going to change just one thing: the tilt of the laser. First you will observe Water at 0°
(entering head-on) and then Water at 60° (entering at an angle). Don't measure the beam or read the
protractor: just decide whether it keeps going straight or changes direction.

The lab interface stays in Spanish; each important label is translated below.

Quick route before you open the lab: Agua (Water) + Normal → observe 0° → press once
and wait → repeat until 60° → return to TEACH. You do not need to measure angles or
understand every technical word on screen.

Fill in the two rows with what you saw, not with what you predicted. If you couldn't follow
the beam, return to 60° using step 7. If it still isn't clear, ask your teacher for the two
backup clues before answering.

Now create one two-panel report — drawn or written — and submit it only once:

- Panel 1 · Water at 0°: show the surface and the path you saw. Mark where the beam enters and add a clue word for what it did there.
- Panel 2 · Water at 60°: show the same surface and the path you saw. Mark where the beam enters and add a clue word for what it did there. Optionally add the dashed reference line from cards A, B and C.

Now compare both materials at 60°: change only the material, then bring the setting back to
60° when you return to Observation. The dashed reference line has a scientific name:
the normal, the line perpendicular to the surface exactly where the beam enters.
That way you can compare whether two transparent materials bend light in exactly the same way.

Don't mix up the names: Normal, with a capital letter, is a setup option on the lab
screen; the normal is the dashed line in the drawing.

Your two clues let you close the case. First write your own explanation without hunting for a
perfect sentence: use what you recorded at 0° and at 60°.

Now compare your verdict with the scientific explanation: at 0°,
the beam enters head-on and does not change direction; at 60°, it enters at an angle and
changes direction as it crosses from the air into the water. That change is called refraction.

In the lab you only decided whether the beam changed direction; now complete the comparison: as
it enters the water, it moves toward the dashed reference line. The card that matches the
observation is B. If you predicted A or C, that's fine: predicting before observing and
correcting an idea with evidence is exactly what investigators do.

With the straw, the journey happens in reverse. Light from the submerged part travels out of the
water into the air and bends the opposite way, away from that reference direction. Our eyes tend to assume it arrived in a straight
line, which is why the submerged part looks shifted. The straw is whole; what changed was the
path of the light.