AP Physics 1: Algebra-Based Flashcards: Conservation of Linear Momentum
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 16 cards to help you master important concepts.
State the principle of conservation of linear momentum.
If the net external force on a selected system is zero, the total momentum of the system is constant.
Card 1 of 16
All Flashcards (16)
State the principle of conservation of linear momentum.
If the net external force on a selected system is zero, the total momentum of the system is constant.
Two billiard balls collide. How can you use conservation of linear momentum to describe their behavior?
The total momentum of the two-ball system before the collision is equal to the total momentum of the system after the collision, assuming no external forces like friction.
How does the choice of a system's boundary affect whether its momentum is conserved?
The selection of a system determines which forces are external, and only a net external force can change the system's total momentum.
A person walks from the back to the front of a canoe resting in still water. Why does the canoe move backward?
The person-canoe system has zero initial momentum. As the person gains forward momentum, the canoe must gain an equal and opposite momentum to keep the system's total momentum conserved.
How can a system of many moving objects be simplified for analysis?
The collection of objects with their individual momenta can be described as one system with a single center-of-mass velocity.
What does a constant center-of-mass velocity imply about the forces on a system?
It implies that there is no net external force acting on the system.
A rocket in deep space expels gas. If the system is defined as the rocket AND the gas, is its total momentum conserved?
Yes, because the forces between the rocket and gas are internal. With no net external forces, the total momentum of the rocket-gas system is constant.
Two ice skaters at rest push off from each other. Describe the momentum of the system consisting of both skaters.
The system's initial momentum is zero. After they push off, the momentum of one skater is equivalent and opposite to the other's, so the total momentum remains zero.
A bomb at rest explodes into many fragments. What can be said about the total momentum of all fragments combined, immediately after the explosion?
Since the initial momentum was zero and the explosion forces are internal, the vector sum of the momenta of all fragments must be zero.
If you observe that a system's total momentum is changing, what can you conclude?
You can conclude that there must be a net external force acting on the system, as this is the only way to change a system's total momentum.
What happens to a system's center-of-mass velocity in the absence of a net external force?
The velocity of a system's center of mass remains constant in the absence of a net external force.
Within an isolated system, how are changes in momentum balanced?
Any change to the momentum of an object must be balanced by an equivalent and opposite change of momentum elsewhere within the system.
How is the total momentum of a system calculated?
The total momentum of a system is the sum of the momenta of the system's constituent parts.
What is the center-of-mass velocity?
It is a single velocity that can be used to describe a collection of objects with individual momenta as one system.
In what types of interactions is momentum conserved?
Momentum is conserved in all interactions, including collisions and explosions.
What is the fundamental condition for the conservation of a system's linear momentum?
If the net external force on the selected system is zero, the total momentum of the system is constant.