{"id":67889,"date":"2026-09-29T04:46:19","date_gmt":"2026-09-28T19:46:19","guid":{"rendered":"https:\/\/phys-edu.net\/wp\/?p=67889"},"modified":"2026-09-29T04:46:19","modified_gmt":"2026-09-28T19:46:19","slug":"we-crashed-a-dynamics-cart-into-a-target-what-the-graphs-reveal-about-the-secret-of-speed-squared-a-kinetic-energy-experiment","status":"publish","type":"post","link":"https:\/\/phys-edu.net\/wp\/?p=67889&lang=en","title":{"rendered":"We Crashed a Dynamics Cart into a Target! What the Graphs Reveal About the Secret of “Speed Squared” (A Kinetic Energy Experiment)"},"content":{"rendered":"

“If your speed doubles, how much harder is the crash?”<\/p>\n

When car accidents make the news, “excessive speed” is often blamed. That’s because even a small increase in speed makes the impact far worse than you’d expect. The secret behind it is something familiar from physics class: kinetic energy<\/b>.<\/p>\n

So what does kinetic energy depend on? When I asked my students for their hypotheses, the words “mass” and “velocity” came up.<\/p>\n

This experiment is usually done on a small scale, rolling a marble down a rail into a target. My twist this time was to crash a 1 kg dynamics cart<\/b> into a target box and work out the answer from how far the box gets pushed. Going bigger makes the results much easier to interpret. Here’s how it works.<\/p>\n

What You’ll Need<\/h3>\n

\"\"<\/p>\n

    \n
  • Dynamics cart\u2026 It has a mass of 1 kg.<\/li>\n
  • Weights (500 g) x 2\u2026 I used two 500 g blocks of oil-based clay as a substitute. Put one on the cart and it becomes 1.5 kg, put on two and it’s 2 kg, so you can easily change the cart’s mass<\/b>.<\/li>\n
  • Beespi\u2026 A simple speedometer.<\/li>\n
  • Bamboo ruler<\/li>\n
  • Disposable chopsticks<\/li>\n
  • Ticker timer<\/li>\n
  • Masking tape\u2026 Used to mark spots on the desk.<\/li>\n
  • Target (box)\u2026 I made mine by stuffing some oil-based clay into a bento lunch container. It’s nice that you can build it from everyday items.<\/li>\n<\/ul>\n

    How to Do It<\/h3>\n

    1. Tape a chopstick to the dynamics cart with masking tape. Then set up the target and run the cart through the Beespi to measure its speed right before it hits the target<\/b>.<\/p>\n

    \"\"<\/p>\n

    2. Vary the speed (between 0.20 and 0.80 m\/s), crash the cart into the target, and record how far the target gets dragged.<\/p>\n