Skateboards, Hills, and the Energy That Never Disappears

Hi, I'm Lumi! Let's talk about energy — the ability to make something happen or move. When an object is moving, it carries kinetic energy. A rolling skateboard, a thrown ball, even you running all have kinetic energy. Two things decide how much: mass (how much stuff is in the object) and speed (how fast it moves). Here is the key pattern: if you double the mass of a moving object while keeping speed the same, its kinetic energy doubles. But if you double the speed while keeping mass the same, kinetic energy quadruples — it goes up by four times. Speed is squared in the formula, so even a small speed boost gives a big energy boost. That is why a fast car in a crash does far more damage than a slow one. See the compare table below: | Change | Effect on kinetic energy | |---|---| | Mass ×2 (speed same) | KE ×2 | | Speed ×2 (mass same) | KE ×4 | Now look at a skateboard resting at the top of a ramp. It has no kinetic energy yet, but it has stored energy called potential energy because of its high position. The higher it sits, the more potential energy it holds. The big idea: energy is never created out of nothing and never truly destroyed. As the skateboard rolls down, potential energy converts into kinetic energy — so it speeds up. Rolling back up, kinetic energy converts back into potential energy as it slows. (Some of that energy also turns into heat from friction — the rubbing between the skateboard wheels and the ramp — but the total amount of energy stays the same.) If this feels tricky, try the sorting activity below, then take the quiz one question at a time.