# Circular Motion - Physics 101 / AP Physics 1 Review with Dianna Cowern | Summary and Q&A

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October 15, 2020
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Physics Girl
Circular Motion - Physics 101 / AP Physics 1 Review with Dianna Cowern

## TL;DR

This content explores circular motion and centripetal forces, discussing the key concepts and equations involved in understanding and calculating them.

## Key Insights

• π Circular motion requires a centripetal force, which is directed towards the center of the circle.
• π§βπ­ The magnitude of the centripetal force is determined by factors like mass, velocity, and radius of the circular path.
• π¦ Centripetal forces have practical applications, such as designing banked roads and creating artificial gravity in rotating cylinders.
• πΆοΈ The concept of centripetal force was instrumental in discovering dark matter and understanding galaxy rotation.
• π Understanding circular motion and centripetal forces requires considering both linear velocity and angular velocity.
• β The derivation of the centripetal force equation involves calculus and is similar to the derivation of equations for oscillatory motion.
• πΉ Circular motion phenomena can be observed in various scales, from skateboard tricks to planetary orbits.

## Transcript

There's this skateboarding trick that only about 15 people have ever successfully pulled off. It's insane. It's a drop from a ramp into a full 360 loop, and it's so hard, because you have to get enough speed to go all the way around, but not too much speed that you get slammed against the wall. Two years ago, I was watching a couple more skaters at... Read More

## Questions & Answers

### Q: What is centripetal force?

Centripetal force is the force that keeps an object moving in a circular path. It is directed towards the center of the circle and is necessary to counteract the object's tendency to move in a straight line due to inertia.

### Q: How is the magnitude of the centripetal force determined?

The magnitude of the centripetal force can be calculated using the equation F = mv^2 / r, where F is the force, m is the mass of the object, v is its linear velocity, and r is the radius of the circular path.

### Q: How was the concept of centripetal force used to discover dark matter?

Scientists observed that galaxies were rotating too fast for gravity to hold them together, indicating the presence of extra mass. This led to the hypothesis of dark matter, which makes up 85% of the universe's matter and was discovered using the concept of circular motion and centripetal forces.

### Q: What is the difference between centripetal force and centrifugal force?

Centripetal force is the force that keeps an object moving in a circular path, directed towards the center of the circle. Centrifugal force, on the other hand, is often considered a fictitious force and refers to the outward force perceived by an object in a rotating reference frame. In the context of this content, only centripetal force is discussed.

## Summary & Key Takeaways

• Circular motion requires a centripetal force to keep an object traveling in a circle, as explained by Newton's first law and the concept of inertia.

• The centripetal force is directed towards the center of the circle and is proportional to the mass, velocity, and inversely proportional to the radius of the circular path.

• The concept of centripetal force was used to solve the mystery of galaxies rotating too fast for gravity to hold them together, leading to the hypothesis of dark matter.