Question

The value of the momentum for a system is the same at a later time as at an earlier time if there are no a) collisions between particles within the system. b) inelastic collisions between particles within the system. c) changes of momentum of individual particles within the system. d) internal forces acting between particles within the system. e) external forces acting on particles of the system.

Short answer

Answer: The conservation of momentum in a system is not maintained when external forces are acting on particles of the system.

Step-by-step solution

Review the principle of conservation of momentum

The principle of conservation of momentum states that the total momentum of a closed system remains constant if no external forces are acting on it. In other words, the sum of the momenta of all the particles in the system at an initial time is equal to the sum of the momenta of all the particles at a later time, provided there are no external forces.

Analyze the answer choices

To determine the correct choice, let's analyze the conditions given in each option. a) collisions between particles within the system: Collisions between particles can lead to a change in each particle's momentum, but the total momentum of the system is still conserved. b) inelastic collisions between particles within the system: Even in inelastic collisions, the total momentum of the system is conserved, though the internal energy of the system may change. c) changes of momentum of individual particles within the system: Individual particles' momentum can change due to internal forces, but this change does not affect the total momentum of the system. d) internal forces acting between particles within the system: Internal forces may cause individual particle's momentum to change, but the total momentum of the system is conserved as long as internal forces remain balanced. e) external forces acting on particles of the system: External forces can cause a change in the total momentum of the system, leading to a violation of momentum conservation.

Choose the correct answer

From the analysis above, the correct answer is (e) external forces acting on particles of the system. This is because momentum conservation holds if there are no external forces acting upon the system.

Key concepts

Physics Education

Physics education aims to impart a foundational understanding of the natural world through the study of matter, energy, and their interactions. Momentum, a key concept in physics, describes the quantity of motion an object has and is crucial for solving problems related to movement and collisions. To effectively educate students in physics, it is essential to present complex topics, like momentum conservation, in an accessible and engaging way.

One teaching strategy involves breaking down principles into real-world scenarios. For instance, by comparing momentum to the push needed to start a swing, students can visualize its impact without delving immediately into more abstract mathematical formulas. Hands-on experiments, such as car collision simulations with toy vehicles, help students observe the principles in action, enhancing the learning experience.

Momentum Conservation Principle

The momentum conservation principle is a fundamental concept in physics, asserting that within a closed system with no external forces, the total momentum remains constant over time. This means that if you add up the momentum of every object in the system at one moment, that sum will be the same at any other moment, despite individual changes in the objects' momenta.

To illustrate, imagine a game of pool. When the cue ball strikes other balls, each ball’s speed and direction might change, but the sum of their momenta, accounting for mass and velocity, remains the same as it was before the strike, unless friction or other outside influences act on them.

Inelastic Collisions

Inelastic collisions are encounters between two or more objects where they collide and move together as a single mass post-collision, meaning that they do not bounce off each other completely. This type of collision typically occurs when objects are sticky, or when they cause each other to deform, as with a lump of clay hitting the ground.

In terms of momentum conservation, inelastic collisions still adhere to the principle. Despite the appearance that some energy has been 'lost' to factors like heat or sound, the total momentum before and after the collision remains the same. It's a common misconception among students that inelastic collisions break the rules of momentum conservation when, in fact, they serve as perfect examples to solidify understanding of the principle in action.

External Forces

External forces are forces that originate outside of the system under consideration and have the potential to alter the state of motion of the objects within that system. Examples include forces such as gravity, friction, or a push or pull from an object not included in the system.

In the context of momentum conservation, it is important to recognize when external forces are acting because they can change the total momentum of a system. For example, if a ball rolling on the ground suddenly hits a sticky spot, the force of friction (an external force) would slow down the ball, changing its momentum. This interaction demonstrates that even though internal forces can redistribute momentum among components of a system, it's the external forces that can disrupt the conservation balance and alter the combined momentum.