Changes in Momentum Worked Examples | Momentum and Impulse | AP Physics 1 | Khan Academy

TL;DR

When two objects collide, the change in momentum between them must be equal and opposite, according to Newton's third law. This principle allows us to solve for various variables using conservation of momentum.

Transcript

• [Instructor] So, here's a pink ball rolling toward a green cube that's sitting at rest on a frictionless surface. When the pink ball hits and slams into the green cube, it's gonna exert a force to the right on the green cube and the green cube's gonna speed up. But because of Newton's third law, whatever force the pink ball exerts on the green cu... Read More

Key Insights

• 💥 Newton's third law states that the forces exerted between two objects in a collision are equal and opposite.
• 💥 Conservation of momentum applies to all collisions, regardless of mass or initial motion.
• 💆 Momentum is a vector quantity, depending on both the mass and velocity of an object.
• ⌛ The impulse, which is the product of force and time, determines the change in momentum.
• 👻 Conservation of momentum allows us to solve for unknown variables in collision problems.
• ❓ The total momentum of a system remains constant in the absence of external forces.
• 💱 External forces can cause a change in the total momentum of a system.

Questions & Answers

Q: How does the conservation of momentum work in a collision between two objects?

In a collision, the change in momentum of one object is equal and opposite to the change in momentum of the other object. This is because the forces exerted by the objects on each other are equal and opposite, according to Newton's third law.

Q: Can the conservation of momentum be applied to objects with different masses?

Yes, the conservation of momentum applies to objects with different masses. The change in momentum of each object depends on its mass and velocity, but the total change in momentum of the system remains the same.

Q: What is the role of time in conservation of momentum?

The time of contact between two colliding objects is crucial for calculating the change in momentum. The longer the contact time, the greater the change in momentum. The impulse, which is the product of force and time, determines the change in momentum.

Q: How does an external force affect the conservation of momentum?

An external force, such as gravity or friction, can cause a change in the total momentum of a system. In this case, the initial and final momentum will not be equal. The change in momentum is determined by multiplying the external force by the time it is applied.

Summary & Key Takeaways

• When two objects collide, they exert equal and opposite forces on each other due to Newton's third law.

• The momentum gained by one object is equal to the momentum lost by the other object.

• Conservation of momentum allows us to solve for unknown values by equating the initial and final momentum of a system.