Reveal the Invisible Force! Exploring Action and Reaction with a Force Sensor

Hi, I’m Ken Kuwako, your Science Trainer. To me, every day is a new experiment!

“If only we could actually see force…” Have you ever felt that way while sitting in a science class—or perhaps while teaching one? In the world of physics, “force” is the foundation of everything. However, because it is invisible, trying to imagine it solely in your head is a monumental task. For many middle school students, mechanics becomes the first major wall they hit in their studies.

Digital sensor technology is the tool that vividly brings this “invisible world” to light. While people often shy away from these devices thinking they are too expensive or difficult to set up, having just one for demonstrations can dramatically increase how much a lesson resonates with students. Today, I want to introduce an experiment using my favorite tools—Narika’s “EasySense” and “Force Sensors”—to visualize a vital principle of physics: Newton’s Third Law, also known as the Law of Action and Reaction.

Visualizing Invisible Force: The Magic of the Force Sensor

A major turning point in understanding physics is whether or not a person can perceive force as a “vector” (something with both direction and magnitude). This is exactly where the Force Sensor comes to the rescue.

The most iconic example of a force you can “see” through data is the Law of Action and Reaction. You know the one: “If you punch a wall, the wall punches you back with the same amount of force.” Even if we understand the logic, it is difficult to capture the exact moment two identical forces act in opposite directions. In this experiment, we use two sensors and set them up so that one moves in a positive direction while the other moves in a negative direction on the graph. This allows us to visualize the movement of force as if it were reflecting in a mirror.

Science Recipe: Witnessing Action and Reaction

What You Need

EasySense, 2 Force Sensors, Windows PC, Ultrasonic Sensor, 2 Dynamics Carts, and weights.

This is the Force Sensor.

The Method

Attach a force sensor to each of the two dynamics carts.

Face the carts toward each other and let them collide.

Add a weight to one of the carts (changing its mass) and try the collision again.

Experiment Results: The Mirror World Appears in Real-Time

When you perform the experiment, the changes in force are recorded on the computer screen in real-time. First, let’s look at what happens when we gently press the two force sensors against each other.

In the video, you can see the green and blue lines appearing in opposite directions as the pressure is applied. When one line creates a peak, the other creates a valley. The graph perfectly highlights the reality of “pushing and being pushed back.”

In this specific trial, the zero-point calibration on one sensor was a bit off, so the numbers look slightly misaligned. However, you can still clearly see that “forces of almost identical magnitude occur at the exact same timing in opposite directions.”

The Scientific World Revealed by This Experiment

The fascinating thing about this experiment is how a law that seems “obvious” on paper manifests as a complex, dancing curve. No matter how irregularly a human applies force, the opposing sensor reacts instantly, returning a mirror-image force without a hair’s breadth of difference.

The Law of Action and Reaction is the reason we can walk by pushing off the ground, and it’s the principle that allows rockets to blast off into space. “Whenever you apply a force, you are always receiving a force in return.” Once you experience this universal rule through a graph, you’ll start to see every phenomenon around you as an “exchange of force.”

While we focused on action and reaction today, force sensors are useful in many other scenarios. For example, if you attach one to the weight of a pendulum, you can graph the changes in tension and acceleration as it swings.

I highly encourage everyone to try these sensor experiments in your classrooms or for independent research projects to capture these invisible forces. If any teachers out there have other creative ways to use these tools, I’d love to hear them! Let’s enjoy “visualizing” science together.

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