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Learning the difference between energy that is waiting to be used and energy in motion.
Imagine you are standing at the very top of a giant slide. You aren't moving yet, but you can feel the 'power' waiting inside you. Did you know that just by sitting there, you are actually full of energy?
Energy isn't just about running and jumping. Sometimes, energy is just sitting still, waiting to be used! We call this Potential Energy. Think of it as 'stored' energy. The higher up an object is, or the more it is stretched, the more potential energy it has.
Imagine a rubber band. When it is just sitting on the table, it has very little energy. But when you pull it back and stretch it, it is now packed with Potential Energy. It is 'waiting' to snap back! In physics, we often look at how much energy is stored based on an object's position. If we used a simple scale, we might say:
when you are at the top of a hill!
Let's look at how height changes stored energy: 1. Pick up your backpack and hold it 1 inch off the floor. It has a little bit of Potential Energy. 2. Now, lift it high above your head. 3. Because it is higher up, it now has much more Potential Energy. If you let go, it has a long way to fall!
Quick Check
If a ball is sitting on the floor and another ball is sitting on a high shelf, which one has more potential energy?
Answer
The ball on the high shelf has more potential energy because it is higher up.
What happens when that 'waiting' energy finally starts to move? It turns into Kinetic Energy. Kinetic energy is the energy of motion. Anything that is moving—a flying bird, a rolling car, or a buzzing bee—has kinetic energy.
The amount of kinetic energy depends on two things: how heavy the object is and how fast it is moving. A fast runner has more kinetic energy than a slow walker. If we were to write it like a scientist, we would see that speed is very important for energy:
This means if you double your speed, your energy actually goes up by four times!
Imagine two balls rolling down a lane: 1. A light tennis ball rolls at miles per hour. 2. A heavy bowling ball rolls at the same miles per hour. 3. The bowling ball has more Kinetic Energy because it has more 'mass' (it is heavier), even though they are going the same speed!
Quick Check
Does a parked car have kinetic energy?
Answer
No, because it is not moving. Kinetic energy is only for objects in motion.
Energy is like a shapeshifter; it loves to change forms! On a playground, you are constantly switching between Potential and Kinetic energy.
When you climb to the top of a slide, you are building up your Potential Energy. As soon as you nudge forward and start to slide down, that stored energy 'transforms' into Kinetic Energy. By the time you reach the bottom, you are going your fastest, which means your kinetic energy is at its highest!
In a perfect world, the total amount of energy stays the same; it just moves from the 'stored' bucket to the 'moving' bucket.
A swing is the perfect energy machine: 1. At the very highest point of the swing (the back), you stop for a split second. Here, Potential Energy is at . 2. As you swing forward, you speed up. Your Potential Energy is turning into Kinetic Energy. 3. At the very bottom of the arc, you are moving fastest. Here, Kinetic Energy is at its highest point! 4. As you rise up again, you slow down, turning that motion back into stored Potential Energy.
Which of these is the best example of Potential Energy?
If you increase the speed of a moving object, what happens to its Kinetic Energy?
Energy can change from potential energy into kinetic energy.
Review Tomorrow
Tomorrow morning, look at three objects in your room. Can you tell which ones have potential energy and which ones have kinetic energy?
Practice Activity
Find a rubber band. Gently stretch it (Potential) and let it go (Kinetic) toward a safe target. Notice how the further you stretch it, the faster it flies!