Conservation of Energy
Conservation of energy is a key idea in physics, and we can explore this using common items.
If we consider dropping a bouncy ball from a set height, we notice that the ball does not rebound to the same height. With each bounce, the ball loses height until it eventually stops bouncing. Why is this?
When the ball is raised by our hand in the air, it gains “potential energy” (this means that it will move downwards when it is dropped). Once the ball is dropped, it falls and its potential energy becomes “kinetic energy” (energy from movement). When the ball hits the floor and begins to travel back upwards, the kinetic energy is converted to potential energy as the ball gains height.
At the highest point, all the ball’s energy is potential; when the ball is on the floor, all the energy is kinetic. If the transition of potential to kinetic energy were perfect, the ball would return to its starting height and would bounce in this way forever. This is because energy cannot be created or destroyed; it is conserved. So why does the ball stop bouncing in real life?
When the ball strikes the ground, some of the energy is transferred to sound and heat energy, meaning that the amount of kinetic energy decreases, so at its highest point, the ball must have a lower amount of potential energy. This means that the maximum height reached by the ball must decrease. As this happens repeatedly, the ball eventually comes to a stop.
In the image below, we can see that the height of the ball at the top of each bounce decreases as some energy is transferred to heat and sound energy as the ball hits the floor.
Similarly, the height a swing reaches will reduce over time until the swing comes to a stop. This is because energy is transferred from the swing to the surrounding air particles.
