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

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December 19, 2020
by
Physics Girl
Rotation and Torque - Physics 101 / AP Physics 1 Review with Dianna Cowern

## TL;DR

This video explains the concept of rotational motion, angular velocity, and torque, and how they are related to everyday objects like the Earth, doors, screwdrivers, and records.

## Key Insights

• 💨 Objects in rotational motion have an angular velocity, which describes how fast they are rotating around an axis.
• ❓ The rotational motion of the Earth generates centrifugal and centripetal forces, which create an imbalance in the normal force experienced by objects on its surface.
• ❓ Torque is the rotational analog of force and is responsible for creating rotational motion.
• ❓ Torque depends on the force applied and the distance from the axis of rotation at which the force is applied.
• 🪈 Understanding torque is essential for explaining the behavior of spinning objects, such as records and screwdrivers.
• 🥺 Special relativity predicts that completely rigid objects do not exist due to the contraction of moving objects, leading to twisting or deformation.

## Transcript

HOST: These are a bunch of random objects. And when I toss them in the air, they seem to wobble. They follow weird, strange paths. But watch what happens when I put them against a dark background with a fluorescent dot at a special place on the object. Now they follow a smooth, perfectly curved path. It's like they don't even have any shape anymore... Read More

### Q: How is rotational motion different from linear motion?

Rotational motion involves objects spinning around a fixed axis, while linear motion involves objects moving in a straight line with no rotation.

### Q: What is angular velocity, and how is it calculated?

Angular velocity is the rate at which an object rotates, measured in radians per second. It is calculated by dividing the change in angle by the change in time.

### Q: What is torque, and how does it relate to force?

Torque is the rotational equivalent of force. It is the product of the force applied to an object and the distance from the axis of rotation at which the force is applied. A larger torque results in a greater rotational acceleration.

### Q: How does torque affect the motion of a screwdriver?

Torque allows the screwdriver to multiply the force applied by the hand, making it easier to drive screws. By applying a small force at a larger distance from the axis of rotation, the torque exerted on the screw is increased.

### Q: Why do doors have their handles at the edge instead of the middle?

Placing the handle at the edge of a door allows for a greater torque to be exerted when opening or closing the door. This makes it easier to apply force and rotate the door.

## Summary & Key Takeaways

• The video starts by discussing how objects in rotational motion can be described and how they differ from objects moving in a straight line.

• It explains how to calculate the angular velocity and linear velocity of an object in rotational motion, using the example of the Earth's rotation.

• The video then introduces the concept of torque, which is the rotational equivalent of force, and explains its role in making objects spin.

• Several examples are provided to illustrate the application of torque, including the case of a bug clinging to a spinning record and the use of torque in screwdrivers.