Launching soon on Google Play
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Charge-Drop is coming to Android. Follow us for previews, physics challenges and launch day.
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What is Charge-Drop?
Charge-Drop is a physics game for Android in which you are an electron. Reflexes alone won’t get you far: you need to understand how electric charges attract and repel.
- Real physics: because the electron is negatively charged, positive charges attract it and negative charges repel it.
- A worldwide leaderboard to measure your score against players everywhere.
- Class codes: your teacher can give you a code so your points reach their gradebook. It’s optional: the game is fully playable without one.
- Free, with adverts and an optional purchase to remove them.
- Respects your privacy: it doesn’t ask for your name, email address, phone number or location.
Try it now: the charge lab
Warm up before launch. The electron shoots off to the right: place positive (+) or negative (−) charges to bend its path into the goal. There are three levels, and the last one is a real challenge.
The arrows show the electric field: the direction it would push a positive charge. Being negative, the electron accelerates the opposite way. Beat level 3? Record it and tag us on TikTok: @extropiahoy.
Physics
Charge-Drop grew out of classroom physics. This section gathers the theory behind the game, starting with electromagnetism.
Electromagnetism
1. Electric charge
Electric charge is a property of matter, and it comes in two kinds: positive and negative. Like charges repel and opposite charges attract. The electron carries the negative elementary charge, e = −1.602 × 10⁻¹⁹ C. Charge is always conserved and comes in whole multiples of e: we say it is quantised.
2. Coulomb’s law
F = k · |q₁ · q₂| / r²k ≈ 8.99 × 10⁹ N·m²/C² · r = distance between the charges
The force between two charges falls with the square of the distance: double the distance and the force drops to a quarter. That’s why, in the lab, the charges closest to the electron dominate its path.
3. Electric field
E = F / q ⟶ F = q · EUnits: N/C. The field points in the direction of the force on a positive test charge.
The electric field describes how a charge changes the space around it. With several charges, the total field is the vector sum of each one’s field (the superposition principle). Because the electron’s charge is negative, the force it feels points against the field.
4. Energy and motion
Each charge creates an electric potential V = kq/r, and a charge q at that point has potential energy U = qV. Without friction, total energy is conserved: the speed the electron gains approaching a positive charge is lost again as it moves away. That’s why it sometimes overshoots or orbits instead of stopping.
Test yourself
If the distance between two charges triples, what happens to the force?
It drops to 1/9 of its original value, because the force depends on 1/r² and 3² = 9.
An electron sits in an electric field pointing right. Which way does it accelerate?
To the left. With F = qE and q negative, the force points against the field.
What is the force between two electrons 1 nm apart?
F = k·e²/r² = (8.99 × 10⁹)(1.602 × 10⁻¹⁹)² / (10⁻⁹)² ≈ 2.3 × 10⁻¹⁰ N, and it is repulsive because both charges are negative.
Coming soon: electric potential, capacitors, magnetic fields and the Lorentz force.
For teachers
Charge-Drop is designed for the classroom too. You can give each student a one-time class code: once they enter it, the points they score are reported to your gradebook. Because the game is fully playable without a code, it also works as an extra challenge or optional homework.
Interested in using it with your class? Get in touch.
FAQ
When does Charge-Drop come out?
Very soon, on Google Play for Android. Follow us on TikTok or YouTube, or leave your email above, and we’ll let you know on launch day.
How much does it cost?
It’s free, with adverts. There’s an optional purchase to remove them.
What data does the app collect?
It doesn’t ask for your name, email address, phone number or location. Adverts are supplied by Google AdMob, and players under 16 are never shown personalised adverts. See the Charge-Drop privacy policy for details.
Do I need a class code to play?
No. The code is optional; it only sends your points to your teacher.
Why don’t you ask for my phone number?
We ask for the minimum. Following us needs no data at all, and the email is optional, used once and then deleted.
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Development updates, physics challenges and the launch announcement, first on our channels.