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

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October 8, 2020
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Physics Girl
Friction - Physics 101 / AP Physics 1 Review with Dianna Cowern

## TL;DR

Friction is a force that resists motion and is caused by the interaction between surfaces. It can be calculated using the equation Ff = μFn, where Ff is the friction force, μ is the coefficient of friction, and Fn is the normal force. Inclined planes affect the amount of friction and can be used to measure the coefficient of friction between two surfaces.

## Key Insights

• ☄️ Friction is a force that resists motion and comes from the interaction between surfaces.
• 🎚️ Surfaces may appear smooth, but at a microscopic level, they still have bumps and roughness that cause friction.
• ❓ Friction depends on the coefficient of friction and the normal force at the interface between two surfaces.
• 🛝 The coefficient of friction can be determined experimentally by measuring the angle at which an object starts sliding on an inclined plane.
• 💋 Friction is essential for daily activities, preventing us from constantly slipping and sliding.
• 🛝 Different surfaces have different coefficients of friction, which affect how easily an object can slide.
• 🛝 Kinetic friction is the force that opposes the motion of sliding objects, while static friction prevents objects from starting to slide.
• ❓ Friction forces can be calculated using the equation Ff = μFn, where Ff is the friction force, μ is the coefficient of friction, and Fn is the normal force.

## Transcript

HOST: So, apparently, ice blocking is a thing. You put a towel on top of a block of ice and slide down that on a grassy hill. And it's so ridiculously fun. And as a 31-year-old child, I visited a park recently to try it out and ended up with grass in more places than I imagined. But it motivated today's lesson, because I tried the same scooting wit... Read More

## Questions & Answers

### Q: What is the difference between kinetic friction and static friction?

Kinetic friction occurs when two surfaces are in motion relative to each other, while static friction occurs when the surfaces are at rest. Kinetic friction is usually smaller than static friction for the same surfaces.

### Q: How can the coefficient of friction be measured?

One method is to slowly increase the angle of an inclined plane until an object just starts to slide. The tangent of this angle can be used to determine the coefficient of friction.

### Q: What factors affect the amount of friction between two surfaces?

The type of surfaces and the normal force exerted between them determine the amount of friction. Rough surfaces and larger normal forces result in greater friction.

### Q: Can friction be completely eliminated?

Friction can be reduced but not completely eliminated. In the absence of any external force, objects in space experience negligible friction due to the lack of interaction between surfaces.

## Summary & Key Takeaways

• Friction is a force that opposes motion and occurs due to the interaction between surfaces.

• Friction can be classified as kinetic friction (for objects in motion) and static friction (for objects at rest).

• The amount of friction depends on the coefficient of friction (μ) and the normal force (Fn) between the surfaces. The equation Ff = μFn is used to calculate friction.