Teaching with a Projector: Simulations for the Whole Class

Teaching with a projector is still the fastest way to get thirty students looking at the same idea at the same moment. A simulation on the big screen turns that moment into an experiment: you change one thing, the whole class sees what happens, and everyone has something to argue about. This guide shows how to run that kind of whole-class demo well with Simulic. You will set up present mode, move students onto their own devices with a QR code, run a demo step by step, and use questioning techniques that make every student think, not just the three who always raise their hands. It ends with three worked demos in physics, chemistry and biology, with the real values each simulation shows.

If you are new to simulations in class, start with the broader guide to interactive simulations in the classroom. This article goes deeper into the projector part.

Why a whole-class demo is worth the time

A projector demo is not a lecture with moving pictures. Done well, it does three jobs that individual work does badly:

• It creates a shared question. When everyone predicts the same event, the discussion has a focus. With thirty students on thirty screens, you get thirty different explorations and no common point to discuss.
• It surfaces misconceptions in public. If half the class predicts that the heavier ball lands first, you know it right away and everyone sees the evidence together.
• It models how to use the simulation. Students who watch you change one variable at a time copy that habit when they work alone.

The trade-off is that students only watch. Keep demos short (8–12 minutes per cycle) and hand the simulation over to students as soon as the shared question is answered.

Set up present mode before class

Present mode shows a simulation on the class screen without the clutter students need on their own devices.

1. Open the simulation page, click Share and, on the Simulation tab, set the starting values for your demo. These values are pinned to the link you create next.
2. On the Share Links tab, under New link, name the link ("Period 4 · demo") and click Create link.
3. On the link card, click Present. The link opens in a new tab in present mode, which is the play link with ?present=1 at the end. You can also type ?present=1 after any play link yourself.
4. Use Fullscreen so the simulation fills the projector, and Restart to run it again from the start.

Present mode shows only the simulation. Questions and prediction locks attached to the link do not appear, so the demo never stalls on a question meant for students. When students open the same link on their own devices, they do see the questions.

Before the lesson, open the present link on the classroom computer, not just your laptop. Check three things: text is readable from the back row (zoom the browser to 125–150% if it isn't), the projector shows the whole simulation, and the school network does not block simulic.com.

Move students onto their own devices: Show QR code

At some point the class should stop watching and start testing. In present mode, click Show QR code. A large QR code fills the screen with the short address underneath. Students scan it with a phone or tablet, or type the address on a laptop, and the simulation opens on their device with any questions you attached. Close the QR code with the × and carry on with the demo.

This takes about 30 seconds and needs no accounts. Students type a nickname only if the link has questions. For older classes you can skip the QR code and post the link in your LMS or Teams instead; see how to share a simulation in Microsoft Teams.

Running a whole-class demo step by step

This routine follows the Predict–Observe–Explain cycle, adapted for one screen and a whole class.

1. Write one question on the board before the simulation is visible. "Will it fall back, circle the Earth or escape?" is a question. "Let's look at orbits" is not.
2. Show the setup without running anything. Name each control you will use and its current value. Point at the screen. Students cannot predict what they don't understand.
3. Make everyone commit. Use mini-whiteboards, think-pair-share or a hinge question (below). No one watches until everyone has an answer.
4. Run it once in silence. Ask students to watch one specific thing: the bulb, the graph, the landing point.
5. Press Restart and run it again while students narrate. "What do you see now? And now?"
6. Ask students to explain before you do. Take two or three explanations, including one that is wrong, then give the scientific model.
7. Change one variable and repeat steps 3–6 quickly. The second cycle takes half the time of the first.
8. Hand over. Show the QR code and give students a target to find on their own, such as a value, a threshold or a pattern.

Questioning techniques that involve everyone

Think-pair-share

Ask the question, then give 30 seconds of silent thinking (no talking, no writing on the board), one minute to compare with a neighbor, and then call on pairs. Pairs are more willing to share an answer they agreed on, and the silent time stops fast students from setting the answer for everyone. Use this for "why" questions and open predictions.

Hinge questions

A hinge question is a multiple-choice question where every wrong option points to a known misconception. The whole class answers at once with fingers (1–4) or ABCD cards, and within a minute you decide: move on, or deal with the misconception now. A good hinge question takes ten seconds to answer and ten seconds to read across the room. Each demo below includes one. For how to build these into a sequence, read using simulations for formative assessment.

Mini-whiteboards

Whiteboards are best for numbers and sketches: "Write the pH", "Sketch the graph you expect". Count down "3, 2, 1, show" so nobody copies. Scan the room, pick two different answers and ask both students to defend them before you run the simulation.

Whatever the technique, wait at least three seconds after a question before taking an answer, and choose who answers instead of taking hands. Both habits raise the number of students who actually think.

Demo 1: Newton's cannon (physics, about 12 minutes)

Use Newton's Cannon 3D, which fires a ball horizontally from an imaginary mountain on a 3D Earth. Pin Mountain height h = 400 km and v₀ = 7 km/s, with "Keep old orbits" on. The simulation needs 3D graphics, so test it on the classroom computer first.

Commit. "The ball leaves the mountain at 7 km/s, about 25,000 km/h. Will it fall back, circle the Earth or escape?" Most students choose "circle": 7 km/s sounds impossibly fast.

Observe. Press Fire. The ball falls back to Earth thousands of kilometers away. The panel shows why: at 400 km, the circular orbital speed is 7.67 km/s and the escape speed is 10.85 km/s.

Vary. Press the "v₀ = vI (circular)" button and fire again: a circular orbit with a period of about 92 minutes, the same height and period as a space station. Then set v₀ = 9 km/s: an ellipse whose farthest point is about 8,560 km up, with a period of about 3.1 hours.

Hinge question. "At 9 km/s, the period will be: A) shorter than 92 minutes, B) the same, C) longer, D) it won't come back." Answer C. A means students think "faster means a quicker lap", B means they think the period is fixed by the height, and D means they think anything faster than orbit escapes. Then fire at 11 km/s to settle D: above 10.85 km/s, the ball escapes.

Demo 2: Strong vs weak acids (chemistry, about 10 minutes)

Use Strong vs Weak Acids. Pin the weak acid as CH₃COOH (ethanoic acid) and the concentration at 0.1 M. The screen shows two beakers side by side: HCl and ethanoic acid at the same concentration.

Commit (mini-whiteboards). "Both acids are 0.1 M. Write the pH you expect for each." Many students write the same number twice.

Observe. HCl has a pH of 1.00. Ethanoic acid has a pH of about 2.88, with a degree of ionization α of about 1.3%, roughly 1 molecule in 76. The HCl bulb glows bright and the ethanoic acid bulb is dim, because there are about 76 times more H⁺ ions in the HCl beaker.

Vary. Press Add Mg. HCl bubbles much faster. Then ask the hinge question before the reaction finishes: "Which beaker gives more hydrogen in the end? A) HCl, B) ethanoic acid, C) the same, D) neither, because the weak acid won't react." Answer C: both beakers hold the same amount of acid, so the final volume of H₂ is the same. The weak acid is just slower.

Extend. Press Dilute 10×. Ethanoic acid at 0.01 M has a pH of about 3.39, and α rises to about 4.1%. Ask pairs to explain how α can go up while [H⁺] goes down.

Demo 3: Herd immunity (biology, about 12 minutes)

Use Disease spread and herd immunity, an SIR model of 100,000 people. Pin the disease as COVID-19 (original strain, R₀ ≈ 3), vaccination at 0% and contact reduction at 0%.

Observe first. Show the unchecked outbreak: note the peak day, the peak size and whether the red line crosses hospital capacity.

Think-pair-share. "What percentage of people must be vaccinated so the outbreak cannot take off?" Pairs usually guess 50% or 100%.

Reveal. The panel shows the herd-immunity threshold 1 − 1/R₀ = 67%. But the vaccine here is about 70% effective, so the panel asks for at least 96% coverage. Drag Vaccination up and watch the curve flatten. At 95% the outbreak still just takes off (Rₑ is a hair above 1); at 96% the text changes to "The outbreak does not take off". Ask why 95% isn't quite enough: that near miss is a discussion point in itself.

Vary. Set contact reduction to 20% (masks, distancing). Now the outbreak stops at about 84% vaccination, because Rₑ = 3 × 0.8 × (1 − 0.7 × 0.84) ≈ 1. Then try measles (R₀ ≈ 15): the threshold is 93%, and with a 97% effective vaccine the panel asks for at least 97%. Seasonal flu (R₀ ≈ 1.5) needs only about 56%.

Hinge question. "Contact reduction 50% and vaccination 30%. Does the COVID-19 outbreak take off? A) yes; B) no, because 50% + 30% is above the 67% threshold; C) no, because halving contacts is enough on its own; D) it starts, then stops within a week." Answer A: Rₑ = 3 × 0.5 × (1 − 0.3 × 0.7) ≈ 1.2, still above 1. B means students add percentages instead of multiplying the effects; C means they forget that R₀ = 3 halved is still 1.5.

After the demo: hand it to the students

The demo answers one shared question. Students learn more when they then answer their own. Show the QR code and set a target that needs the same simulation:

• Physics: "Find the lowest speed that still gives an orbit from a 1,000 km mountain."
• Chemistry: "Find a concentration where ethanoic acid's α is above 10%." (At 0.001 M it is about 12%.)
• Biology: "Find the lowest vaccination rate that stops measles with 30% contact reduction."

Attach a question set to the link to collect the answers: up to five questions, including number questions checked automatically with a tolerance. Students answer under the simulation with a nickname, and you see the results table on the Share page. For writing those questions, see how to add simulations to quiz questions.

Common projector problems

• Text too small. Zoom the browser before the lesson, and use Fullscreen.
• The 3D simulation shows a WebGL message. The classroom computer cannot run 3D graphics. Try another browser, or turn on hardware acceleration.
• The projector cuts off the edges. Set the computer to duplicate (mirror) the display at the projector's resolution.
• Students' devices can't open the link. A school filter may block simulic.com. Ask IT to allow it, and keep the demo running on the projector in the meantime.

FAQ

What is present mode?

It is a share link opened with ?present=1 at the end, or with the Present button on the Share page. It shows the simulation for the class screen, with Restart, Fullscreen and Show QR code buttons, and hides the questions.

Do students need accounts to join from the QR code?

No. They scan the code and the simulation opens. If the link has questions, they type a nickname.

Can I use present mode in an online lesson?

Yes. Share your screen in the video call, and post the play link in the chat instead of showing the QR code.

How long should a projector demo take?

One predict-observe-explain cycle takes 8–12 minutes. Two cycles with a change of variable is a good maximum before students take over.

Can I show a simulation without creating a link first?

You can project any simulation page, but present mode and the QR code work on share links. Creating a link takes a few seconds and lets you pin the starting values.