Circular Motion AIM: How is this even possible?????

But First…Facts about Circular Motion

More Facts about Circular Motion

Even More Facts about Circular Motion Velocity (tangent to the circle at all times) Centripetal Acceleration and Centripetal Force (always towards the center of the circle) V FcFc acac

What Provides Centripetal Force? Centripetal force is a NET force which means it is calculated – either by Newton’s 2 nd Law (F c =ma c ) – Or by drawing a free body diagram and determining the net force from the orientation of the forces on the diagram. Because it is a net force, you should use the same steps you were using (hopefully) last topic.

Friction as a Centripetal Force (running, driving) On a level surface, friction IS the force that keeps the object (car, motorcycle, person) moving in a circle. – This is a STATIC friction force because the tires/shoes are not skidding across the surface. – Does the mass of the car affect its maximum turning speed? JUSTIFY! Vertical Horizontal FfFf FNFN FgFg

Examples 1.A 200Kg motorcycle with rubber tires wants to complete a turn of radius 12m on a level dry asphalt road as fast as possible. a.What is the max static friction force between the road and the tires? b.What is the max speed the motorcycle can take the turn? c.Compared to the speed of the motorcycle, what would be the maximum speed a 400kg car could take the turn? 2.A 65Kg runner takes a turn of radius 15m at 7.5m/s. a.What is the friction force required to make this turn? b.What is the coefficient of friction between the shoe and the track? c.Is this a static or kinetic coefficient? WHY?

Friction on an Inclined Surface FfFf FNFN FgFg   Vertical Horizontal

Tension as the Centripetal Force An object moves in a horizontal circle on a frictionless surface while attached to a string of length l Table top T

Tension as the Centripetal Force An object moves in a vertical circle on a at a constant speed while attached to a string of length l T FgFg

Tension as the Centripetal Force An object moves in a vertical circle on a at a constant speed while attached to a string of length l T FgFg

Tension as the Centripetal Force When an object is moving in a vertical circle, where in the motion is the string most likely going to break? JUSTIFY! As seen in the equations above, the tension in the rope at the top of the circle is the centripetal force minus the weight of the object because at that point, gravity is providing some of the centripetal force. At the bottom, the tension in the rope is the centripetal force plus the weight because at that point, the tension not only has to hold up the weight of the object, it must also provide the centripetal force.

Tension as the Centripetal Force An object moves in a conical pendulum while attached to a string of length l making an angle  with the vertical T FgFg  TyTy TxTx

Normal Force as a Centripetal Force (Gravitron Ride) When you are riding the gravitron, the centripetal force is provided by the wall of the ride! Does the mass of the rider matter? – PROVE IT MATHEMATICALLY! FfFf FNFN FgFg Vertical Horizontal

Examples 1.A 60Kg student rides a gravitron with a radius of 7m. The ride completes 10 revolutions in 1 minute a.What is the average speed of the rider? b.What is the normal force provided by the wall? c.What is the coefficient of friction between the rider and the wall 2.An average person can tolerate an acceleration of 4g before passing out. If you wanted to build a gravitron ride with a radius of 12m a.What is the maximum average speed you can set the ride to? b.What would have to be the coefficient of friction between the wall and the person to make the ride successful?

Circular motion in a Vertical Loop At the TOP of the loop FNFN FgFg If you ‘just make it’ F N =0N

Circular motion in a Vertical Loop At the BOTTOM of the loop FNFN FgFg

Circular motion in a Vertical Loop Where in the loop do you feel the heaviest? JUSTIFY! You feel heaviest at the bottom of the loop because your ‘apparent weight’ is the normal force. At the bottom the normal force has to counteract the weight and provide the centripetal force. At the top, some of the centripetal force is provided by gravity.

Examples 1.A 60Kg student rides a rollercoaster with a vertical loop with a radius of 15m. a.What is the minimum speed needed to complete the vertical loop? b.If the actual speed of the ride at the top is 20m/s, how heavy (F N ) does the rider feel at the top of the loop? c.If the ride’s speed is 31m/s at the bottom, how heavy do they feel? 2.A 3kg set of keys attached to a 0.75m long string in being swung in a vertical loop. a. Assuming the maximum tension the string can provide is 140N, how fast can the keys be swung without breaking the string?

Circular motion on a Hill At the TOP of the hill FNFN FgFg If you ‘lose contact with the seat’ F N =0N

Examples 1.A 50Kg student rides a rollercoaster with a circular hill that has a radius of 20m a.What is the maximum speed the coaster can take the hill before the student loses contact with the seat? 2.If you want a 300kg motorcycle to be able to stay in contact while driving over a circular hill at 40m/s. What is the radius of the hill?

Gravity as a Centripetal Force

Newton’s Law of Gravity F g Force of gravitational attraction between any two objects. GUniversal Gravitational Constant=6.67x Nm 2 /kg 2 m the mass of the objects (kg) r the distance between the CENTERS of the objects.

Acceleration Due to Gravity General g

Orbital Speed

General Orbital Speed-> Kepler’s 3rd Laws

Kepler’s Laws of Planetary Motion 1.The law of ellipses: all planets orbit the sun in elliptical paths with the sun at one focus. 2.The law of equal areas: As a planet orbits the sun, it sweeps out equal areas in equal amounts of time. This means the closer the planet is to the sun, the faster it is moving. 3.The law of harmonies: the orbits of all the planets’ orbits are related

Questions How could have scientists figure out the mass of the Earth? How could have scientists figure out the mass of the sun? How could have scientists figure out the distances to all the other planets in our solar system?