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What things move in a circular path?

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Presentation on theme: "What things move in a circular path?"— Presentation transcript:

1 What things move in a circular path?
amusement rides planets & moons car driving a curve (part of a circle) lasso merry-go-round racetrack jet fighter wash machine centrifuge

2 What are the two types of circular motion?

3 Rotation vs Revolution
Object turns about in ___________ axis Rotation: Object turns about an __________ axis

4 Circular Motion (Material from Ch 10 - 12)
How do Newton’s Laws apply to Circular Motion?

5 Newton’s First Law - Inertia
States that every object continues in a state of rest or uniform speed in a straight line unless acted upon by an net force…. Ex. Spinning bike tire will burn your hand if you try to stop it – heat/friction force

6 Newton’s 2nd Law Forcenet = mass x acceleration or
acceleration = Net Force/mass The Force is perpendicular to the lever arm.

7 Newton’s 3rd Law of Motion
For every action there is an equal and opposite reaction.

8 You are on a merry-go-round rotating with a constant speed
You are on a merry-go-round rotating with a constant speed. Is there a net force acting on you? Yes No

9 If a stopper is twirled on a string and the string suddenly breaks, the stopper will move in which direction? 4 3 1 2 Path 1 Path 2 Path 3 Path 4 52 of 61

10 Implications for Circular Motion
What does Newton’s 2nd Law imply about objects moving in a circle? The state of motion is always changing so a net force MUST be acting. The centripetal (center-seeking) force keeps the object from moving in a straight line. The object accelerates away from its straight line path.

11 10.3 Centripetal Force The force exerted on a whirling can is _______________________________. No outward force acts on the can.

12 Centrifugal Force NO SUCH THING!!! Centrifugal means center-fleeing
Not a force but a feeling we get due to the inertia of our bodies wanting to continue in a straight line. Don’t use the f-word!!!

13 Equations for Circular Motion
speed, acceleration, centripetal force,

14 Sample Problem: Curved/Circular Motion
A car is taking a 52 m radius curve at 21 m/s. The car’s mass is 1015 kg. a) What is the acceleration of the car? b) What amount of force is acting on a passenger whose mass is 58 kg? c) What amount of force is acting on the car?

15 a) a = (21m/s)2/52m a = 8.5 m/s2 b) F = 58kg(8.5m/s2) F = 490 N
c) F = 1015kg(8.5m/s2) F = 8600 N v F a r = 52 m, v = 21 m/s, mc = 1015 kg, mp = 58 kg

16 The astronauts move in a circular orbit around the earth
The astronauts move in a circular orbit around the earth. Why do they appear to be “weightless”? A. There is no gravity in space and they do not weigh anything. B. Space is a vacuum and there is no gravity in a vacuum. C. Space is a vacuum and there is no air resistance in a vacuum. D. None of the above

17 Astronauts and “Weightlessness”
Astronauts and Shuttle falling away from straight line path at same rate There IS gravity acting on both of them! v v a F a F Demo: bucket of water rotated overhead To avoid confusion, NASA now uses the term microgravity instead of weightlessness

18 Rotor Ride Fc a v Ff Fc W Top View Side View
into video: pause to discuss why feel pushed against door when take curve. Fc W

19 10.2 Rotational Speed _____ parts of the turntable rotate at the same _____________ speed or ______s. A point farther away from the center travels a ________ path in the ________ time and therefore has a ____________ tangential or linear speed. A ladybug sitting twice as far from the center moves ___________ as fast.

20 10.2 Rotational Speed think!
At an amusement park, you and a friend sit on a large rotating disk. You sit at the edge and have a rotational speed of 4 RPM and a linear speed of 6 m/s. Your friend sits halfway to the center. What is her rotational speed? What is her linear speed?


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