Report

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 = 2 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?? 2 = 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 “centerSeeking” Force pushes you toward the center of the circle Is the force that keeps you moving in a circle, and keeps your inertia from taking you in a straight line Centripetal Force is affected by.. Mass (m), linear speed (vt), and radius (r) 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 Below, a record spinning on a axis through its center (black dot) 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