Collisions (physics)
Collisions in physics refer to events where two or more moving objects come into contact, exerting forces on each other for a brief moment. During these interactions, momentum—a measure of the motion of an object—is exchanged between the colliding bodies. The principle of conservation of momentum dictates that the total momentum of the system remains constant before and after the collision, although the momentum of individual objects may change. There are two primary types of collisions: elastic and inelastic. In an elastic collision, the total kinetic energy is conserved, while in an inelastic collision, some kinetic energy is transformed into other forms, such as thermal energy or sound. A specific case of inelastic collisions is a perfectly inelastic collision, where the colliding objects stick together post-collision, maximizing energy loss. Understanding these concepts is grounded in Newton's laws of motion, which describe how forces affect the motion of objects, emphasizing that a greater mass requires more force to achieve the same acceleration. Overall, the study of collisions is essential for analyzing interactions in various physical scenarios, from everyday objects to complex systems.
On this Page
Collisions (physics)
Collisions in physics occur when two or more moving objects exert forces on each other for a brief time. During a collision, these forces cause an exchange of energy known as momentum. Collisions adhere to a fundamental law of physics called the conservation of momentum. This law states that the total momentum of objects involved in a collision will remain the same before and after the collision. The momentum of individual objects may change, but the total must remain the same. Two types of collisions exist, each categorized by whether energy is conserved or converted to other forms during the impact.
Overview
The physics that govern collisions follow the laws of motion discovered by English physicist Isaac Newton in the seventeenth century. Newton's second law of motion states that the force acting on an object is equal to the mass of that object times its acceleration. This means that when a force acts on an object, acceleration is produced. The more mass an object has, the more force is needed to produce acceleration. Other important concepts in collisions—impulse and momentum—are offshoots of this law. Since collisions occur for only a brief time, an impulse is a measure of force multiplied by time. Momentum is equal to mass times velocity. For example, if a bowling ball and a baseball are rolling down a street at the same velocity, the bowling ball will have more momentum because it has more mass.
In a collision, the force exerted by moving objects causes a change of momentum. The size of this momentum change depends on the amount of time the force acts on the object. According to the law of conservation of momentum, the total momentum—mass times velocity—will not change during the collision but can shift between objects. An example of this can be seen on a pool table when the cue ball strikes another ball. The cue ball may lose velocity, but the target ball gains what the cue ball lost and moves in another direction. This example is not perfect, as the conservation of momentum applies only to a closed system, an environment in which no external forces are acting upon it. On a pool table, some momentum is lost to the external force of friction between the balls and the table surface.
While the same fundamental laws apply to all collisions, the two types of collisions depend on how kinetic energy is distributed during impact. Kinetic energy is the energy produced by the motion of an object. An elastic collision typically occurs between two objects that are solid, such as the balls on a pool table. When the balls collide, little or no loss of kinetic energy occurs. An inelastic collision occurs when kinetic energy is converted to another form of energy, such as thermal energy or sound. In a perfect inelastic collision, a maximum amount of kinetic energy is lost, allowing the two objects to stick together after colliding, such as when an arrow sticks into its target after being fired.
Bibliography
Avison, John. The World of Physics, 2nd ed. Oxford University Press, 2014.
"Conservation of Momentum." National Aeronautics and Space Administration, www.grc.nasa.gov/www/k-12/airplane/conmo.html. Accessed 3 Jan. 2023.
"Elastic and Inelastic Collisions." HyperPhysics, hyperphysics.phy-astr.gsu.edu/hbase/elacol.html. Accessed 20 Dec. 2016.
"Linear Momentum and Collisions." Tennessee Tech University, www2.tntech.edu/leap/murdock/books/v1chap7.pdf. Accessed 3 Jan. 2023.
Matolyak, John, and Ajawad Haija. "Linear Momentum and Collision." Essential Physics. CRC Press, 2014, pp. 121–138.
"Momentum and Collisions." Real World Physics Problems, www.real-world-physics-problems.com/momentum.html. Accessed 20 Dec. 2016.
"Momentum and Collisions—Background Material." School of Physics—University of New South Wales, www.animations.physics.unsw.edu.au/jw/momentum.html. Accessed 20 Dec. 2016.
Myers, Rusty L. The Basics of Physics. Greenwood Press, 2006.