CH. 9

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# CH. 9 - PowerPoint PPT Presentation

Circular Motion. CH. 9 . Rotation &amp; 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
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
• Ex. Daily motion of the Earth, spiral football
• Revolution
• Object rotating about an external axis
• Ex. Yearly motion of the earth
Centripetal Acceleration
• 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
Centripetal Force

?

• 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??
So why is there no Force pushing you out from the circle??
• 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 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),

Centripetal Force
• 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
Centrifugal force
• Spin cycle in laundry
• Phone sliding off dashboard
• Dog shake
The Rotor

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.

Videos
• “G-Forces”
• NASA Centrifuge
• Centrifuge Training
• 9G test run
• Gross (negative G’s)
• Another 9 G test run
How do we describe how fast something is rotating??
• 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
Are all people on Earth moving at the same speed??
• 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