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GCSE weather · 15 minutes · no login

Wind, PGF and Coriolis

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Field photograph or official scientific figure for teaching wind. A second photograph for the projector script — not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CC

Why this lesson, and why the 3D

Wind, PGF and Coriolis is a fifteen-minute projector lesson, not a homework packet and not a film with a quiz bolted on. Put this hook on the board before you dim the lights: Air starts downhill on the pressure slope. Earth then twists the path. By the end of the slot a pupil should be able to name PGF, switch Coriolis on, compare NH and SH, and add friction near the surface. Curriculum tags in the header (GCSE weather; A-level atmosphere; NGSS HS-ESS2) are filters, not a flag. The room is worldwide; SI first; International English. Ages on the card (GCSE, A-level, NGSS MS, HS Earth Sci) are a suggested band, not a gate.

Met Office isobars are this lab printed on a chart. A UK depression approaching London, a Great Plains nocturnal jet arguing with friction, and a Denver lee trough are the same three ideas: pressure-gradient force, Coriolis, friction. GCSE wants the names and the spin. A-level wants geostrophic balance and why surface winds cut across isobars toward low. NGSS wants a rotating Earth that deflects, not a magic force in the room. If pupils think Coriolis swirls a sink, they will never trust a weather chart. If they skip friction, they will never see why air piles into a low at the ground. Start downhill on the pressure slope. Then twist. Then slow it. Florida’s latitude still has Coriolis; a playground sea breeze does not need it. Scale first, then the keys.

The 3D is a named, inspectable object. Click the part, not a caption. If the model will not spin, the Why panel still carries the mechanism, the two photographs, and the film. Do not apologise for the model. Drive it. A silent spin teaches a screensaver. A named mesh that changes under a slider teaches the process.

Fifteen minutes on the projector

Toggle Coriolis off. PGF only: high to low, straight down the pressure slope. Toggle Coriolis on. In the northern hemisphere the path deflects right. Toggle Southern hemisphere. Deflection flips left. Coriolis is an apparent deflection because we measure on a rotating Earth. You cannot point at it in the room. Toggle Friction on. Surface flow cuts across isobars toward low. Geostrophic is PGF versus Coriolis with friction neglected. Ask which arrow a textbook pair is missing. Coriolis does not make water swirl in a sink. Basin scale is too small. Weather systems are large enough. Sinks are not. Coriolis is zero at the equator and largest at the poles. London feels it; a washbasin does not. Finish in Check.

Open the lab full screen (F). Labels on (L). Speak the first step before you touch a slider: High to low: the PGF arrow. No spin yet, so flow is straight down the slope. Then the second: Coriolis on. NH left-looking-downslope becomes a right deflection. Toggle SH. Add friction: surface flow cuts across isobars toward low. Then the third: Geostrophic is PGF vs Coriolis, no friction. The ground slows the wind and lets PGF win a bit.

The sliders that earn their keep are Coriolis; Friction; Southern hemisphere. Space plays; arrows nudge time; R resets. Parameters the URL can remember: coriolis, friction, sh. If you only have eight minutes, skip the last step and finish in Check. Projector layout (P) is for the back row: one idea, large type, the model still live.

Toggle Coriolis off first so PGF is the only arrow. Space plays the flow. Arrow keys nudge time. L hides labels; ask which way is downhill before you reveal. R resets Coriolis, friction, and hemisphere. P is projector. Then Coriolis on, then Southern hemisphere, then Friction. Time is not a year clock; the drive is the three toggles and a pause for the geostrophic pair. Share the URL when the surface arrows cut across isobars, and again with friction off so the textbook balance is a link the class can reopen.

The in-site film is “Where Does Wind Come From? Crash Course Geography #8” (Crash Course Geography, about 11 min, Crash Course / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off.). Autoplay is off. Play one minute if you need a second voice; do not let the film eat the slot. The 3D still has to move under your hand.

What the third row will get wrong

You will hear the misconception before you have finished the first sentence. Write the false claim on the board and leave it there until the model has contradicted it. Do not skip this. A fluent pupil can recite the hook and still believe the false sentence.

“Coriolis makes water swirl in a sink.” — no. Basin scale is too small. Weather systems are large enough. Sinks are not.

“Coriolis is a real force you can point at in the room.” — no. It is an apparent deflection because we measure on a rotating Earth. You cannot hang a label on a bit of air and call it Coriolis.

“Friction makes the wind faster.” — no. Friction slows the wind. Weaker Coriolis then lets PGF pull the surface flow across isobars toward low.

Pitfalls to keep in your pocket: Coriolis as a real force you can point at in the room. NH vs SH mix-up. Sinks and toilets as evidence. Teaching friction as something that speeds the wind. Do not let a pupil leave thinking the 3D is a photograph. It is a teaching model. Where vertical exaggeration exists, T collapses it and the caption says so. A labelled lie of scale is honest. An unlabelled one is a cartoon.

Two places, not a slogan

Air starts because pressure is uneven: the pressure-gradient force (PGF) points from high to low, downhill on the pressure surface. With no rotation and no friction, flow would run straight down that slope. We measure on a rotating Earth, so the path appears to deflect: right of the motion in the northern hemisphere, left in the southern. That apparent deflection is Coriolis. It is zero at the equator and largest at the poles. It is not a force you can point at in the room, and it does not run a bathroom sink; basin scale is too small, weather systems are large enough. Geostrophic wind is PGF balanced by Coriolis with friction neglected, flow along the isobars. Near the ground, friction slows the wind. Weaker wind means weaker Coriolis, so PGF wins a bit and the surface flow cuts across isobars toward low. That is why lows fill from below and why a UK surface chart is not a replica of the 500 hPa chart. Toggle Southern hemisphere and the deflection flips. Toggle Friction and the arrows bite toward the low. Leave Coriolis off once so the class sees the naked slope.

The first place to land is Met Office isobars. The second is US Great Plains. Same process, different rock or climate. If a pupil can only name one place, they have a postcard, not a mechanism. Atlas entries for those names are a click from the case list; send them back to the lab with one sentence they can say in Check.

Do not flatten the comparison into “this country versus that country.” Name the landform. Holderness is till, not chalk. Hawaii is a hotspot, not an island arc. Yosemite is a glacial trough, not a river canyon. The 3D is allowed to be schematic; the place names are not allowed to be sloppy.

Figures and the film

Field photograph: Ripples on sand: wind as a visible agent. Pressure gradient plus Coriolis plus friction. Credit: Wikimedia Commons, CC BY.

Mechanism photograph: Field photograph or official scientific figure for teaching wind. Field photograph or official scientific figure for teaching wind. A second photograph for the projector script — not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC. Credit: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.

Two photographs, two jobs. The field picture is the place. The mechanism picture is the process. Do not run the lesson on a single Apollo Earth disc. A carbon-cycle class is a forest and a seam, not a blue marble. An ENSO class is a Pacific temperature map, not Africa from Apollo 17.

Words they must be able to say

Say these out loud once while you click the matching mesh. If a word has no mesh, it still has a photograph in Terms.

Coriolis: Apparent deflection because we measure on a rotating Earth. Right in NH, left in SH. Zero at the equator. PGF: Force from high to low pressure, downhill on the pressure surface. Exam language also accepts “Pressure-gradient force”. Geostrophic wind: PGF balanced by Coriolis. Friction neglected. Flow along the isobars. Friction: Surface drag that slows the wind, weakens Coriolis, and lets PGF pull across isobars toward low. Isobar: A line of equal pressure on a chart. Tight packing means a steep PGF. Buys Ballot’s law: In the northern hemisphere, with your back to the wind, low pressure is on the left. School rule of thumb. Pressure gradient: How pressure changes with distance. Steep gradient, strong PGF, strong wind.

Exam-language toggle (the Teacher tab) swaps UK/US pairs where they exist — levée/levee, arête/arete — so a mixed room is not punished for spelling.

Close the slot

If JavaScript or WebGL dies, the 2D fallback still shows high, low, and isobars. Teach from the steps: PGF downhill, Coriolis on, friction across the isobars. Check still names PGF, northern-hemisphere deflection, friction, and the equator. Print the teacher script. The glossary still carries geostrophic wind and Buys Ballot’s law. You lose the moving arrows, not the sink-scale warning. A printed Met Office chart can stand in for the canvas; point downhill, then right, then across the isobars toward low.

Finish in Check — ten questions, not a mood. The bank mixes definition, process, the misconception you just killed, a named place, and a read-the-model item (click the part; T). If a pupil can only recite the hook, they have not used the geometry. Wrong answers still show the one-line explain. Do not skip the explain.

Sources on the Teacher tab are the trail, not a bibliography to copy. Met Office charts; NOAA jet stream.

Link back to the live lab and keep the same slug. Do not invent a parallel worksheet that contradicts T, SI, or the named parts.

This note is worldwide. Curriculum tags (GCSE weather; A-level atmosphere; NGSS HS-ESS2) are filters, not a flag. A class in Nairobi, London, or Shanghai can use the same 3D. Ages (GCSE, A-level, NGSS MS, HS Earth Sci) are a suggested band. If a sentence only works in one exam board, rewrite it before you project it.

Write these three lines on the board before you dim the lights. One: Air starts downhill on the pressure slope. Earth then twists the path. Two: the misconception “Coriolis makes water swirl in a sink.”. Three: the named parts they must click. Then drive the model. Check is ten questions covering definition, process, the misconception, a place, and a read-the-model item. Do not skip the explain on a wrong answer.

Board, units, and what not to say

SI first. Metres, kilometres, degrees Celsius, metres per second. A conversion in brackets is courtesy, not a second system. Do not let a pupil leave thinking the 3D is a photograph. It is a teaching model. Where vertical exaggeration exists, T collapses it and the caption says so.

Do not say “teaching mesh”, “sprinkle”, or “thin free surface not a fat pipe” out loud. Say the landform. Seasons are ~23.44° of axial tilt, not Earth–Sun distance. The outer core is liquid; S-waves do not pass. Yosemite is a glacial U-trough. San Andreas is a transform. Hawaiʻi and Yellowstone are hotspots. Florida is not a glacial trough.

If the room is noisy, projector layout (P) is the back-row setting: one idea, large type, the model still live. Full screen (F). Labels (L). Space plays. Arrows nudge time. R resets. The URL can remember coriolis, friction, sh. Send them home with the same link; there is no login.

In-site film

Where Does Wind Come From? Crash Course Geography #8. Crash Course Geography. Crash Course / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off. Autoplay off.