The Flipping Physics Blog

New Video: Electric Potential due to Scalar Superposition

10/5/2026

Electric potential is a scalar, which makes superposition refreshingly simple. No components, no angles, just add the values together.

In my newest video the class works a problem with two point charges on the x axis. One is a positive 6.0 microcoulomb charge at the origin, the other is unknown, and the total electric potential at 0.40 meters is zero. Before we touch the algebra, I stop the class and ask what we can already say about that unknown charge. It turns out we can pin down both its sign and whether it is bigger or smaller than the first charge, purely by reasoning. Then we solve it and the math agrees.

My favorite part is the end, where Billy asks whether we needed to convert microcoulombs to coulombs, and the answer is no.

New Video: What Does Constant Acceleration Really Mean?

10/4/2026

Acceleration is measured in meters per second squared, but I find a lot of students have an easier time with it when I read those units out loud a different way: meters per second every second. Same units, much clearer meaning.

In my newest video I roll a basketball down an incline with a constant acceleration of 2 meters per second every second, and you can watch the velocity climb by exactly 2 every single second while the acceleration arrow never changes. Then I give the ball an initial velocity of negative 10 meters per second so it rolls up the incline first, slows down, and stops. The acceleration still does not change one bit.

New Video: Adding a Dielectric to a Non-Electrically Isolated Capacitor

9/29/2026

We already know what happens when you add a dielectric to an electrically isolated capacitor. This time the capacitor is connected to a constant power supply, so the electric potential difference is what stays fixed instead of the charge. The capacitance goes up, the charge on the plates goes up, and yet the electric field between the plates does not change at all. Bobby asks the obvious question, which is how that can possibly be true, and Billy follows it up by asking what happened to the induced electric field from the polarized dielectric. Working through both questions is really the heart of this lesson.

New Video: Building a Real Parallel Plate Capacitor

9/28/2026

Aluminum foil, printer paper, a large dictionary, and about 120 pounds of mass. That is all it takes to build a real parallel plate capacitor. In this short video I walk through the build, explain why the dielectric has to extend past the edges of both plates, and measure the capacitance with a multimeter. The reading comes in at 11.73 nanofarads. Check out the video below!

New Video: Capacitor Electric Field Derivation

9/22/2026

In this new lesson, Bobby, Billy, Bo and I derive the equation for the uniform electric field between the plates of a parallel plate capacitor. We start from the capacitance equation we already know, combine it with the definition of capacitance and the relationship between electric potential difference and electric field, and arrive at E = Q divided by the quantity kappa times epsilon naught times area. Then we apply it to the homemade aluminum foil and printer paper capacitor from the previous lesson, solving for both the magnitude of the electric field and the number of excess charge carriers on each plate. We close by answering a great question from Bo: why does the power supply read zero amps?

New Video: Zero Work Along an Equipotential Surface: The Gravitational Comparison

9/21/2026

Why does it take zero work to move a charge at a constant speed along an equipotential surface? Because both forces acting on the charge are perpendicular to its displacement, making the work done by each force zero. A gravitational comparison reinforces the concept: moving a point mass horizontally at constant speed along a surface of uniform gravitational potential also requires zero work. Two different fields, same idea, zero work every time. Check out the video below!

New Video: Electric Field Lines Are Always Perpendicular to Equipotential Surfaces

9/14/2026

In this short video, I demonstrate that electric field lines are always perpendicular to equipotential surfaces across three different cases: a uniform electric field between parallel plates, a positive point charge with radially outward field lines and spherical equipotential surfaces, and an electric dipole with complex curved equipotential surfaces. In every case the angle is always 90 degrees. And that relationship means that if you know one map, you can construct the other. Check out the video below!

New Video: Drop a Ball from a Moving Car: A Projectile Motion Demo for Your Class

9/7/2026

This one is for physics teachers! I have a video where I drop a ball out of a moving car and it lands in a bucket. Several teachers have successfully done this with their own classes and it is a fantastic way to demonstrate projectile motion in real life. In this video I walk through exactly how to set it up, what equipment you need, how to time the drop, and what to watch out for. If you do this with your students, please share the video with me! I would love to create a collage of everyone's attempts. Check out the video below!

New Video: 3 Parts of a Force Graph: Newton's 2nd Law in Real Time

9/6/2026

A cart on a track is pulled by a hanging mass through a string over a pulley. As the cart is held at rest, released to accelerate, and then stopped, a force sensor measures the tension in the string in real time. Three different situations produce three different tension values, and a live force graph captures all of it. Physics demonstrated! Check out the video below!

New Video: AP Physics 1 YouTube Live Kahoot Schedule 2026-2027

9/3/2026

Join Mr. P for a full year of live AP Physics 1 Kahoot quizzes on YouTube! Once a month on a Monday evening, we go live with a 10-question multiple-choice Kahoot covering that unit's content. Every session starts at 7pm Eastern Time, except Review #2 which starts at 8pm. The full schedule for the 2026-2027 school year is in the video description. Check out the video below!