4*7 Circular motion: riding on the curves WDYS??? / WDYT??? You DO NOT fall out of the roller-coaster when it goes upside down during a loop because _____.

4*7 Investigate (p420) Part A: Moving on Curves 1a) The car runs in a _____. 1b) With string attached to car, it now runs in a __. 1d) When string is cut from car, it now runs in a __.

4*7 Investigate (p420) A FORCE is needed for CIRCULAR MOTION… WITHOUT the force, the object moves in a STRAIGHT LINE 2a) The _____ in the string supplies the force. 2b) The force is _____ the center of the circle.

There must be a force pointing toward the center of the curve… 4*7 Investigate (p420) There must be a force pointing toward the center of the curve… 3. The force of _____ between the _____ and the _____ keeps the car moving in a circle. 4. Draw the diagram:

4*7 Investigate (p420) The force moving the cart in a circle will be _____ the center of the circle. 5c) Draw the free- body diagram:

4*7 Investigate (p422) Part B: How much force is required? 1a) The force is acting _____ the center of the circle. 1b) With ONE stopper… As you begin to twirl the stopper, your fingers __________ to supply a force!!!

***This is an example of a _____ relationship*** 4*7 Investigate (p422) 2a) NOW with THREE stoppers… As you INCREASED the mass, your fingers __________ to supply a _____ force ***This is an example of a _____ relationship*** As the mass increases, the force _____. 2b) You can only measure ONE VARIABLE (mass) at a time!!!

4*7 Investigate (p422) 3a) A SMALL circle with ONE stopper… As you begin to twirl the stopper, your fingers __________ to supply a force!!! NOW, a LARGER circle with ONE stopper… As you INCREASED the length/radii, your fingers __________ to supply a _____ force

***This is an example of a _____ relationship*** 4*7 Investigate (p422) ***This is an example of a _____ relationship*** As the length/radii increases, the force _____. 3b) You can only measure ONE VARIABLE (length/radii) at a time!!!

4*7 Investigate (p422) Why don’t you fall out of the roller coaster cart when it goes upside down during a vertical loop??? 5a) As the speed increases, a _____ force is needed to keep it moving in a circle. 5b) As the mass increases, a _____ force is needed to keep it moving in a circle. 5c) As the length/radii decreases, a _____ force is needed to keep it moving in a circle.

On to Vertical Loops… 4*7 Investigate (p422) 4b) Force of fingers when stopper is near the TOP of the circle = __________ Force of fingers when stopper is near the BOTTOM of the circle = __________ 4c) What happens (to the shape) when the string and stopper lose speed???

4*7 Notes(p425): Centripetal Force and Acceleration All objects moving in circles/curves: Require a force toward center of circle Are accelerating EXAMPLE string supplies the force track pushing on wheels Normal Force (FN)  force toward center of circle/curve, its perpendicular in direction

***Centripetal Force is NOT an additional force*** Centripetal Force  force that keeps object moving in a circle/curve; its always directed toward center EXAMPLE force (tension)= string attached to car force (friction)= b/t tires and road force (gravity)= Earth orbits around Sun ***Centripetal Force is NOT an additional force***

Fc = (m × v2 ) r Centripetal Force and Acceleration (Part B Investigate) Centripetal Force is LARGER if: Speed is increased (Direct) Mass is increased (Direct) Radius of circle is decreased (Indirect) Fc = (m × v2 ) r Fc = centripetal force (N) m = mass of object (kg) r = radius of circle (m) v = speed of object (m/s)

EXAMPLE contact force b/t you and seat Newton’s 2nd Law  if there is a net force, then an object must be accelerating (speed up/slow down/change direction) Centripetal Acceleration  acceleration directed toward the center of circle/curve EXAMPLE contact force b/t you and seat ***It’s the centripetal acceleration and contact force that give you the THRILL***

2. Apparent Weight and the Roller-Coaster Ride “Apparently LIGHTER”  Top of loop Contact force is smaller Acceleration is directed downward “Apparently HEAVIER”  Bottom of loop Contact force is greater Acceleration is directed upward

3. Safety on the Roller Coaster 1 g = 10m/s/s  normal gravity 2 g = 20m/s/s 4 g = 40m/s/s  this is the maximum acceleration for a roller coaster!!! 6 g = 60m/s/s  this is what astronauts experience at lift-off!!! 9 g = 90m/s/s causes unconsciousness!!!

In a vertical loop, the DIRECTION OF CENTRIPETAL FORCE (FC) is always changing to ensure that it is always TOWARD THE CENTER OF THE CIRCLE

Draw a Vertical Loop: FC =centripetal force FN = normal force FW = weight/gravitational force

4*7 TOTD If the speed and mass INCREASES, then the force __________. If the size of the circle INCREASES, then the force __________. The THREE factors that make it possible to go UPSIDE-DOWN are: 3. __________ 4. __________ 5. __________

4*7 Checking up (p429): _____ is required to make an object travel in a circle. You (are/are not) accelerating if you are traveling in a circle at a constant speed. At the top of a roller coaster loop, the two forces that provide the centripetal force are 1._____ and 2._____ The force responsible for your apparent weight on a roller coaster is _____. The centripetal force acting on an object depends _____ on the object’s mass. It varies _____ with the radius of the curve. It _____ with the square of the object’s velocity.

4*7 Physics to Go (p433): A) B) An object moving in a circle at a _____speed requires a ______ centripetal force. It (will/will not) be more difficult to make the turn because the mass has increased. A larger mass requires a _____ centripetal force. 8. Draw and Label the picture…AGAIN!!!

4*7 Physics to Go (p433): 10. 14.a) b) c) d) e) f) g) Fast-moving Roller Coaster  Required Centripetal Force Force of Gravity (Weight) Normal Force Top of Loop 4000N 500N Bottom of Loop 6000N Slow-moving Roller Coaster  Required Centripetal Force Force of Gravity (Weight) Normal Force Top of Loop 800N Bottom of Loop 2800N