Two BeeSpies, One Trick! A Mind-Blowing Experiment to Visualize Motion Equations
I’m Ken Kuwako, your science trainer. Every day is an experiment!
Did you know that every movement around us is actually governed by a single, elegant law? From the resistance you feel when pushing a heavy box to the thrilling acceleration of a bike speeding down a hill—these experiences were unlocked through the language of mathematics by Isaac Newton as his Laws of Motion (The Equation of Motion). Today, I want to show you how we can reveal this fundamental rule of the universe using simple tools you’d find in a typical classroom.
The Magic of Two Speedometers
In Japanese science classrooms, the Bee-Spi is a well-known tool for measuring speed.
Usually, it’s used to measure the velocity of an object passing through it. However, if you line up two of these devices, you can accurately calculate acceleration—the rate at which an object’s momentum increases.
The setup is surprisingly simple. Fix two Bee-Spis at a measured distance from each other, and attach a simple wooden chopstick to the front of your cart. As the chopstick passes through the first Bee-Spi, we get the initial velocity; as it hits the second, we get the final velocity. Here is where the physics gets exciting: by plugging those numbers into this formula,
we can calculate acceleration, a force that is usually invisible to the naked eye. You can see the experiment in action here:
The Challenge of Constant Force
The biggest hurdle in this experiment is pulling the cart with a perfectly consistent force. If you try to pull it by hand, the force inevitably fluctuates, making it impossible to gather precise data. To solve this, I used a professional piece of equipment called the Yagami Constant Force Device. This allows us to apply a steady, unwavering pull throughout the entire experiment.
By refining the setup like this, the beautiful laws of nature finally begin to show themselves.
The Rules of the Universe on a Graph
During the experiment, we collect data repeatedly by changing the mass (adding weights to the cart) or adjusting the amount of pulling force. When you plot these values on a graph, a strikingly clear relationship emerges:
a = k F / m
This tells us that acceleration is directly proportional to force and inversely proportional to mass. This very equation, ma = F, discovered by Newton in the 17th century, is the same one used today to launch rockets to the moon and control the brakes on self-driving cars. Isn’t it incredible to think that simple tools like chopsticks and speedometers can connect us to the grand laws that rule the cosmos?
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