# Conservation of Momentum - Physics 101 / AP Physics 1 Review with Dianna Cowern | Summary and Q&A

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December 4, 2020
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Physics Girl
Conservation of Momentum - Physics 101 / AP Physics 1 Review with Dianna Cowern

## TL;DR

Momentum is a fundamental concept in physics that describes the motion of objects. It is related to an object's velocity and mass, and its conservation is observed in various scenarios, including rockets and collisions.

## Key Insights

• 😑 Newton originally expressed his second law of motion using the concept of momentum, which illustrates the importance of the concept.
• ❓ Momentum is a vector quantity, meaning it has both magnitude and direction.
• ❓ Conservation of momentum states that the total momentum of a system remains constant before and after an interaction or event.
• 🚀 Impulse, defined as the change in momentum, helps explain various phenomena like the Leidenfrost effect and rocket propulsion.
• 🚄 Rockets rely on momentum conservation to accelerate forward by expelling a high-speed gas in the opposite direction.
• 🦾 The concept of momentum extends to quantum mechanics, where Heisenberg's uncertainty principle introduces uncertainty in simultaneous position and momentum measurements of quantum objects.

## Transcript

Here's a brain teaser for you. You're on a train, rolling on a track at a constant speed with no friction. And the train is full of sand because you're building a sand castle, obviously. And then the train villains sneak onto the train and drill a hole in the bottom of the train so that the sand starts to flow out the bottom. What happens to the sp... Read More

### Q: What is momentum, and how is it related to an object's velocity and mass?

Momentum describes an object's quantity of motion and is calculated by multiplying its mass and velocity. It determines how difficult it is to change an object's motion.

### Q: How does Newton's second law relate to momentum?

Newton's second law can be written as "F = Δp/Δt," where Δp is the change in momentum and Δt is the change in time. This equation emphasizes that force is proportional to the change in an object's momentum.

### Q: How does impulse affect momentum?

Impulse, which is the product of force and time, leads to a change in momentum. A longer duration of force application reduces the average force required to change momentum, which impacts scenarios like catching a baby or car safety measures.

### Q: How does momentum conservation apply to rockets?

Momentum conservation is crucial in understanding how rockets work. By expelling a mass of gas at high speed, rockets gain momentum in the opposite direction, propelling them forward. Momentum conservation also explains how light from the sun can propel spacecraft, such as LightSail 2.

## Summary & Key Takeaways

• Momentum is a crucial concept in physics for understanding motion, collisions, rockets, and other phenomena.

• Newton's second law, written in terms of momentum, explains that force is proportional to a change in motion.

• Impulse, the product of force and time, is related to momentum and explains phenomena like the Leidenfrost effect and rocket propulsion.