Overview
Collisions are common in many sports and play a significant role in performance, tactics, and injury risk. A collision occurs when two or more bodies or objects come into contact with force, often involving a rapid change in momentum. Understanding the mechanics of collisions, through the lens of momentum, force, and energy transfer, is essential for analysing sporting situations such as tackles, impacts with equipment, or ball striking.
When a collision happens, momentum is a key factor. According to the principle of conservation of momentum, the total momentum of all objects involved before a collision is equal to the total momentum after the collision, provided there are no external forces acting (such as friction or air resistance). This principle helps explain what happens when two players collide in rugby, or when a bat strikes a ball in cricket or baseball.
There are two main types of collisions in sport:
Elastic collisions occur when objects collide and bounce apart, with no loss of kinetic energy. This is rare in human movement, but it may be observed when balls rebound from hard surfaces.
Inelastic collisions occur when objects collide and some of their kinetic energy is lost, typically being converted into heat, sound, or deformation. Most collisions in sports are inelastic- for example, a rugby tackle, where players remain in contact or fall together, losing some momentum due to heat and impact force.
The outcome of a collision depends on the mass and velocity of the objects involved. A heavier or faster-moving athlete will typically generate more momentum and may dominate the collision. However, the way momentum is absorbed or redirected can be influenced by body position, centre of mass, and timing, making technique critical for both safety and effectiveness.
Impulse, defined as force multiplied by time, also plays a significant role in collision dynamics. Increasing the time over which a collision occurs reduces the force experienced by the object. This is why players bend their knees when landing, or why equipment such as pads, gloves, and mats is used—to extend contact time and reduce peak force, thereby lowering the risk of injury.
Collisions aren’t limited to physical contact between players. They also occur when an athlete strikes a ball, hits a target, or lands on the ground. In each case, force is transferred, momentum is changed, and energy is either absorbed or redirected. For example, in football, striking the ball at the right angle with the correct velocity produces an effective collision that transfers energy efficiently and accurately.
Understanding collisions allows for better coaching of tackling techniques, safer equipment design, and more effective movement strategies. It also helps explain how energy and momentum flow through the body or equipment to influence performance, from sprint starts to high-speed impacts in team sports. In all cases, controlling the collision is key to both success and safety.
