- By
**chet** - Follow User

- 106 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Rotational dynamics' - chet

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Rotational dynamics

Chapter 8

Masses

- Up ‘til now, we have assumed that all masses are essentially points in space.
- From this point onwards, we will treat all objects as extended.

Rotation

- We established earlier that centripetal force causes circular motion.
- What causes the centripetal force in the first place?

Rotation

- Remember, for all objects, we are assuming that the object rotates around a fixed axis.
- Objects rotating around this axis feel the centripetal force.

Torque

- The ability of a force to rotate an object around that axis is measured by a quantity known as torque.
- Torque is dependent on three things
- Force
- Lever arm
- The angle between the two

Torque

- Depending on where the force is applied, torque will increase or decrease.
- Torque is a vector

Sample problem

- A mechanic applies a force of 400 N at an angle of 20 degrees on this wrench. The wrench is 0.3 meters long. What is the torque?

Net Torque

- Like force, there can be multiple torques on an object.
- You can add those all up to find the net, or total, torque.
- ∑τ=τ1+τ2+τ3+…
- Keep in mind each torque can be positive or negative, so the net torque will be + or –.

Sample problem

Find the net torque of all the forces on the triangle around the fixed point. (ignore the d’s and f’s in the diagram).

Rotation

- The axis of rotation is easy to find for some objects. Doors, the windows in the back, all have hinges.
- What if something is flying through the air?

Center of Mass

- If gravity is the only force acting on something, that object will rotate about its center of mass.
- This in turn means that airborne objects undergo both linear and rotational motion

Center of mass

- Depending on if the object is symmetrical or not, the center of mass is either easy or hard to find.

Center of Mass

- It’s easier to rotate some objects around a certain axis than others.
- What’s the best way to swing a bat?

Moment of Inertia

- An object’s ability to resist rotational motion is measured by its moment of inertia.
- Mass and moment of inertia both resist motion
- Mass resists linear
- M.o.I resists rotational

Moment of Inertia

- How an object is shaped determines its moment of inertia.
- The further the mass is from the axis, the greater the m.o.i.

Download Presentation

Connecting to Server..