Sticks & Stones Task 3, Lesson 1 The Sling Sticks & Stones Task 3, Lesson 1

Haast’s Eagle The Hunt: Haast’s Eagle The Hunting Tool: The Sling Video: www.youtube.com/watch?v=tnOWdGPbz6c Ask students if they have ever seen or used a sling. Direct students to read about the sling and Hasst’s Eagle in their Project Logs – Task 3 Sling Challenge

Discuss How is the motion of the sling different or similar to the motion of the bow and arrow? Sling Video https://www.youtube.com/watch?v=kikC0Q9m8O8

The Sling: UCM

What is UCM? Uniform Circular Motion: is the motion of an object in a circle with a constant or uniform speed. Direct students to record the definition of UCM in their notes

UCM Group Demo Directions: 5-8 students stand in a circle in the center of the room. Use poles/brooms attempt to push a ball so that it roles in a circle around the group. Which direction do the students have to push the ball in order to turn it? How does the direction of the balls acceleration compare to its velocity? Video: https://www.youtube.com/watch?v=KvCezk9DJfk

Discuss How would you release the sling in order to fire the projectile forwards? What direction would you need to push on an object in order to make it turn in a circle? Circular Motion Video: https://www.youtube.com/watch?v=KvCezk9DJfk https://www.youtube.com/watch?v=fSfVVz0eIis The video can be paused to emphasize the tangential velocity vector. Help students notice that the length of the vector remains the same size (uniform motion…constant speed), but the direction is changing. Note which way the tennis ball moves when the string is clipped. Relate this to the sling and getting the projectile to release in the right direction.

Discuss Why do objects slide toward the outside of your car while you are making a turn? Something is pushing the object outward. The object is traveling in a straight line and you are turning. Both a) and b) are true. Outward motion (video) https://www.youtube.com/watch?v=DLgy6rVV-08

The F-Word! Centrifugal means away from the center or outward. The use of or at least the familiarity with this word centrifugal, combined with the common sensation of an outward lean when experiencing circular motion, often creates or reinforces the misconception. https://www.youtube.com/watch?v=A0H7TYzcMaY https://www.youtube.com/watch?v=hZOekFFSoWI

Investigation Please complete Investigation 4 - Basics of Uniform Circular Motion.

Period/Frequency Period: The time that it takes to complete one cycle. (T) Units: Second (s) Frequency: The amount of cycles per sec. (f) Units: Hertz (Hz)

Angular Velocity The number of rotations per unit time. (RPM) The number of degrees per unit time. The number of radians per unit time. Denoted by a lower case omega, which is a weird looking (ω). Also called rotational velocity. How is angular velocity different than linear velocity?

The relationship between angular and linear velocity v = r ω v = velocity r = radius ω = angular velocity in radians/sec

Acceleration

Force What force causes centripetal motion? ANYTHING! (actually any force) The main forces you will see are: Friction, tension, gravity, normal force, or a combination of these. Is there truly a “centripetal force”? It is just the overall net force of the object. Never label a centripetal force on a FBD.

Net Force

Practice Problem The trainees we are about to see will pull a maximum of 6g’s of acceleration. Assume the centrifuge has a of radius 20m. What is the centripetal acceleration? What is the linear velocity? What is the angular velocity? What is the centripetal force acting on a 60kg rider? Video: https://www.youtube.com/watch?v=EXQKl-28zn0

To Sum It All Up Uniform Circular Motion is: Constant speed. Velocity tangential to the curve. Angular Velocity (rate of rotation). Acceleration toward the center. Centripetal force is just the net force of the object toward the center of the circle.

Documentary Amazing brain centrifuge documentary! https://www.youtube.com/watch?v=RVeHxUVkW4w It time permits, show this documentary.