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Circular Motion Uniform Circular Motion Acceleration
Forces in Circular Motion Banked curves Centripetal forces Centrifugal vs. Centripetal Force
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Uniform Circular Motion
The speed and radius of an object remains constant The velocity vector changes because its direction changes.
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Acceleration A moving body undergoes acceleration if its speed or direction changes. Uniform Circular Motion produces Centripetal Acceleration. “Centripetal” from Latin: Centrum = “centre”; Petere = “to seek”
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Centripetal Acceleration
Centripetal acceleration is an instantaneous acceleration It always acts towards to the center of motion.
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Centripetal Acceleration
………………. It points toward the center of the circular path of motion.
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Check Your Understanding
A child on a merry-go-round is 4.4 m from the centre of the ride, travelling at a constant speed of 1.8 m/s. Determine the magnitude of the child’s centripetal acceleration. Answer: ac = 1.82/4.4 = 0.74 m/s2
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The ac formula can be written as:
…………… For high rates of revolution, it is common to state the frequency rather than period. The frequency f = the number of revolutions per second = 1/T.
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Our Equations for Uniform Circular Motion
If speed (v) is known: If speed is not known but period (T) is: If f is used in place of T due to a high revolution rate
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Check Your Understanding
Determine the frequency and period of rotation of an electric fan if a spot at the end of one fan blade is 15 cm from the centre and has a centripetal acceleration of magnitude 2.37 x 103 m/s2. Answer: T = s/rev f = 2.0 x 10 rev/s
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Forces in Circular Motion
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Analyzing Forces in Uniform Circular Motion
According to Newton’s Second Law, there is a net force acting towards the centre of the circle that causes the centripetal acceleration.
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The equations for centripetal acceleration involving the period and frequency of circular motion can also be combined with the second-law equation. Thus, there are three common ways of writing the equation: Fnet is the magnitude of the net force that causes the circular motion
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Check Your Understanding
A car of mass 1.1 x 103 kg negotiates a level curve at a constant speed of 22 m/s. The curve has a radius of 85 m. Name the force that provides the centripetal acceleration. Determine …………….. Determine the minimum coefficient of static friction needed to keep the car on the road.
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Check Your Understanding
A 3.5-kg steel ball in a structural engineering lab swings on the end of a rigid steel rod at a constant speed in a vertical circle of radius 1.2 m, at a frequency of 1.0 Hz, as shown below. Calculate the magnitude of the tension in the rod due to the mass at the top (A) and the bottom (B) positions. Answers: Position (A) – FT = 1.3 x 102 N Position (B) – FT = 2.0 x 102 N
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Centripetal forces What forces can cause something to move in a circle? Tension, Gravity (components if on earth or full force if considering orbits) Force of Static Friction These forces constantly counteract the bodies desire to move away from the circular path on a tangent. Note: all forces that are centre seeking are centripetal forces
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Centrifugal vs. Centripetal Force
Centrifugal force (Latin for "center fleeing") describes the tendency of an object following a curved path to fly outwards, away from the center of the curve. It's not really a force; it results from inertia i.e. the tendency of an object to resist any change in its state of rest or motion. Centripetal force is a "real" force that counteracts the centrifugal force and ……………..
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Human Centrifuge Rick Mercer in a human centrifuge
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