Photon pressure is the force exerted by light when it strikes a surface. This phenomenon occurs because light consists of particles called photons, which carry momentum. When photons collide with an object, they transfer some of their momentum, creating a small but measurable pressure. This pressure is most noticeable in environments with little to no air resistance, such as in space. For example, solar sails utilize photon pressure to propel spacecraft by capturing sunlight. As photons reflect off the sail, they push it forward, demonstrating how light can exert force despite having no mass.