A ball bounces after hitting the ground due to the law of conservation of energy. When the ball falls, its potential energy is transformed into kinetic energy. When it hits the ground, some of this kinetic energy is stored in the ball, causing it to bounce.
When a ball hits the ground, it temporarily deforms upon contact. This deformation directly depends on the elastic properties of the material it is made of. Some materials store this deformation energy very well, like rubber, and efficiently release it by returning to their original shape — somewhat like the ball being a mini invisible spring. The more efficiently this energy is released, the higher the ball bounces. Other materials, like a modeling clay ball, absorb the energy without returning it, resulting in almost no bounce. This ability to regain its shape after being compressed is called elasticity. The more elastic a material is, the better its chances of bouncing high and hard.
When you drop a ball, it starts with energy called gravitational potential energy, related to its height. As it falls, this energy transforms into kinetic energy, the energy of movement. Upon impact with the ground, the kinetic energy causes the ball to deform for a moment, temporarily storing the energy in elastic form. Then the ball quickly returns to its original shape, releasing this elastic energy and pushing the ball back up. Of course, it doesn’t bounce back as high because some of this energy is lost: vibrations, noise, heating of the material... This is referred to as an imperfect bounce, as the energy is not fully conserved in a form usable by the ball.
When the ball hits the ground, it exerts an upward reaction force. It’s like an invisible spring that compresses for a moment and then pushes the ball upwards. This reaction force comes from the principle of action-reaction: the ball pushes on the ground, and the ground responds by pushing back on the ball. The harder the ball hits, the more intense this reaction is, which explains why a bounce is more pronounced if the fall was from a greater height. Without this push, it's impossible for the ball to go back up. That's why a soft surface, like a thick carpet, offers a weaker reaction and thus a less impressive bounce.
Gravity constantly brings the ball back to the ground after its bounce and concretely determines the maximum height it can reach. The stronger the gravity (like on Jupiter), the faster the ball is pulled to the ground, limiting its bounce height. Conversely, weaker gravity (like on the Moon) allows for a higher, slower, and more expansive bounce. Air resistance gradually slows the ball down by absorbing some of its energy. If the ball is light or very low in density, the air slows its movement both downward and upward, clearly diminishing each subsequent bounce until it comes to a complete stop.
If the ball or the ground has small imperfections, such as scratches or tiny bumps, it can directly influence its bounce. These mini-local deformations change the way the ball interacts with the ground: a very rough surface or a dented ball loses more energy at the moment of the bounce, reducing the bounce height. Conversely, a very smooth surface and a perfectly round ball optimize energy conservation at impact, allowing the ball to bounce higher and more consistently. A textured surface, like that of a tennis ball with its tiny fibers, also slightly alters the friction during impact, affecting the bounce but also sometimes the trajectory after it.
On very soft surfaces like sand or thick grass, a ball will bounce less than it would on a wooden floor or concrete: this is because these surfaces dissipate a significant amount of the ball's energy by deforming or compressing in response.
The balls used in professional tennis must adhere to strict standards regarding their bounce. Indeed, a ball dropped from a height of 254 cm must bounce between 135 cm and 147 cm to be approved for official competitions.
The ambient temperature also affects the bounce of a ball: in cold weather, the material becomes stiffer and more brittle, reducing its elasticity and therefore the height of the bounce. Conversely, in warm weather, it typically bounces better.
There is a world record for the bounce of a rubber ball: when dropped from a height of 30 meters, it bounced back to over 22 meters! This kind of performance is closely related to the elastic properties and the weight of the ball.
Sure! Here’s the translation: "Yes, a hard and smooth surface returns the energy of the ball better, resulting in a higher bounce. In contrast, a soft or uneven surface absorbs more energy, thereby reducing the height of the bounce."
Generally, yes. When heated, a ball becomes softer and more elastic because the molecules move with more energy. This enhances its ability to effectively return energy during a bounce.
With each bounce, a portion of the ball's initial energy dissipates as heat and sound, due to elastic and plastic deformation as well as air resistance. This results in a gradual loss of energy, making an infinite bounce impossible.
At high altitudes, the air is less dense, which reduces the air resistance acting against the ball during the bounce. Thus, a ball will bounce slightly higher at high altitudes than at sea level.
The rebound capacity depends on the elastic properties of the material that makes up the ball. The more elastic a material is, the more efficiently it returns the energy absorbed during impact, thereby enhancing the rebound.
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