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# Ch5 - circular motion and gravity conceptual

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Circular Motion & Gravity, Conceptual Physics

Circular Motion & Gravity, Conceptual Physics

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• 1.  Objects can ROTATE like the earth on its own axis. Rotate: turn about an internal axisObjects can REVOLVE like people on a ride at Great America. Revolution: turn aboutan external axis.
• 2. Objects can also do both at the same time: Like the planets in our solar system. The planets REVOLVE around the sun and ROTATE about their own axis.What rides at Great America do both? Our lesson for this session will only deal with revolutions on a circle. No rotations.
• 3. As the lady bug revolves around The circle what do you notice about The velocity vector? What do you notice about the The acceleration vector Acceleration vector? always points toward the center. This isThe velocity vector is called centripetal always a straight line acceleration. or linear off the circle. This is a tangent line. So this type of velocity is called linear or tangential velocity.
• 4. Now lets get active to learn about the following terms:1. Angular velocity,2. tangential velocity,3. Centripetal accelerationGo to the website and click on the ladybug animation.Have your guided practice available so you can use theanimation and collect some pieces of information.http://www.cabrillo.edu/~jmccullough/Physics/Circular_Motion.html#
• 5. Centripetal means “center-seeking” and centripetal force is nota new special kind of force. It comes in many forms such as tensionand friction.Objects moving in a circle experience a center seeking force called centripetal force. When the bucket is at the top of the circle it does not fall out. Why not? The answer is in Newton’s First Law. Think inertia. The FORCE on the bucket IS toward the center. The tether ball’s tension in the rope is divided into an upward Y force and a center-seeking x force. So the x force is the Centripetal force.
• 6. No matter where the car is on the curve it will experience the center seeking force called centripetal force. Friction keeps the car on the curve. If there was no friction which way would the car slide? The friction is the centripetal force.Centripetalforce
• 7. Remember Newton’s Second Law? F=mxaThis applies to circular motion as well except that the acceleration has a different formula because its circular motion.So for circular motion F = m * ( v2 / r ) F = forcem = massv = linear (tangential velocity) r = radius of circle.
• 8.  A 5 kg object rotates on a string with a velocity of 3 m/s and a radius of 1.5 m. What is the force on the object? F = m * v2 /r m = 5 kg v = 3 m/s r = 1.5 m F = 5 * 32/1.5 Ans: 30 N