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# CH. 9 - PowerPoint PPT Presentation

Circular Motion. CH. 9 . Rotation & Revolution. Axis A straight line through which circular motion takes place All points on object orbit around the axis All rotation/revolution requires an axis Rotation Object rotating about an internal axis

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## PowerPoint Slideshow about ' CH. 9 ' - kuniko

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Presentation Transcript

### CH. 9

• Axis

• A straight line through which circular motion takes place

• All points on object orbit around the axis

• All rotation/revolution requires an axis

• Rotation

• Object rotating about an internal axis

• Ex. Daily motion of the Earth, spiral football

• Revolution

• Object rotating about an external axis

• Ex. Yearly motion of the earth

• Can an object being moving at a constant speed but also have a changing velocity?

• Yes, can be changing direction

• As is the case when an object is moving w/ a constant speed in a circular path

• Changing direction  changing velocity acceleration

?

• When driving in a circle, in what direction is a force acting on you?

• Pushing you outward from the circle, or inward?

• If you are swinging a yo-yo in a circle, and the string breaks…. What path does the yo – yo take??

• Ans. -- Inwards, toward the center of the circle

• Ans -- yo- yo goes in a path tangent to the circle

• HOWEVER, People commonly think there is a force pushing you out from the circle

• Feels like you are being pushed outward

• Example ….. The Rotor- amusement park ride, a centrifuge, CD on your dashboard moving to the right when your turning left

• Why is this??

• A force does not cause this…… your INERTIA does!!

• Inertia makes you want to stay in a straight line, and by going in a circle, you are fighting your own inertia

• This is how Rotor works, and why CD on dashboard happens

• The only actual force acting on you is the

Centripetal Force

• Centripetal means “center- Seeking”

• Force pushes you toward the center of the circle

• Is the force that keeps you

moving in a circle, and

taking you in a straight line

Centripetal Force is affected by.. Mass (m),

linear speed (vt),

• Inertia wants to take objects in a tangent line, to the circular path

• Inertia is why you feel like your being pushed outward

• This outward pushing is sometimes called the Centrifugal Force

• but it is not actually a force, is only inertia

• Every object that moves in circular motion must experience a centripetal force from somewhere

• Spin cycle in laundry

• Phone sliding off dashboard

• Dog shake

People Stand with backs against wall of a large cylinder, cylinder then starts spinning, and people are seemingly pushed against the wall, then floor drops, and people are stuck against the wall.

• “G-Forces”

• NASA Centrifuge

• Centrifuge Training

• 9G test run

• Gross (negative G’s)

• Another 9 G test run

• Speeds for objects in a straight line are called linear (or tangential) speeds,

• Linear speeds are a rate at which an object covers a certain distance (v =d/t)

• Ex. Unit – m/s , km/hr , mph

• Can’t express speeds of rotation with a linear speed,

• b/c objects at different points on the rotating object have different linear speeds

• Rotational speed

• Expresses the rate at which an object rotates through a portion of a circle ( an angle)

• Ex. Unit --- RPM’s

• Faster linear speed, Star or Smiley??

Smiley, travels a greater distance for each

Full spin.

• Faster rotational speed, Star or smiley??

• Both the same, b/c entire record is rotating at the same rate

• Earth is rotating about an axis through its poles

• So that means we are all moving since we are all on the Earth.

• Are some of us moving with a greater LINEAR SPEED than others??

• Yes, closer to the Equator, the faster you are moving…. Closer to poles, the slower you are moving

• Are some of us moving with a greater ROTATIONAL SPEED than others??

• No, all people on earth have same rotational speed, because Earth is spinning at the same rate everywhere