A spring works by storing and releasing potential energy. When an object is pressed down on a spring, the spring compresses and stores potential energy. When the object is released, the spring expands, releasing that stored potential energy and causing the object to bounce back up.

The key mechanisms are:

1. Elasticity: Springs are made of elastic materials that can be deformed and then return to their original shape. This allows them to compress and expand.

2. Potential energy: As the spring is compressed, the deformation of the spring material stores potential energy. This is similar to how compressing a rubber band stores energy.

3. Conservation of energy: When the spring is released, the stored potential energy is converted into kinetic energy, causing the object to accelerate upwards. This acceleration continues until the object reaches its peak height, at which point the kinetic energy is converted back into potential energy.

4. Oscillation: The object will then fall back down, compressing the spring again. This cycle of compression, expansion, and oscillation repeats, causing the bouncing motion.

The combination of elasticity, potential energy storage, and energy conversion allows springs to create this bouncing effect, enabling all sorts of devices and mechanisms that rely on the ability of objects to rebound.