1. Applied - Finau

2. What is circumference? Equation?  Distance around a circle  C = 2πr  π ≈ 3.14  r = radius – distance from center of circle to edge  Important for estimating distance traveled given a radius

3. What’s the difference between rotation and revolution?  Rotation – spinning about an axis  Ex – spinning a basketball on your finger  Revolution – moving around an external object not connected to  Ex – keys swinging on lanyard; grappling hook swung around

4. Does the Earth rotate or revolve?  Both!  It rotates about its axis  This is what causes night and day  It revolves around the sun  1 revolution per year

5. What’s the difference between linear speed and angular speed?  Linear Speed – speed of an object in a straight line  Angular Speed – speed an object rotates or spins at (ie. – how fast it spins)

6. What is linear speed called when it refers to an object moving in a circle?  Tangential Speed  Recall a tangent line – a line that touches a curve at one point  If an object moving in circular motion is let go, it would move tangent to the circle

7. On a merry-go-round, two horses lie in a straight line. Horse A at radius 1 m and horse B at radius 2 m. Which horse travels faster and why?  Both have the same angular speed; they both revolve to the same plane together  Horse B has a greater tangential speed; it travels a farther distance in the same amount of time

8. As the Earth spins, it pulls us along with it. Describe our motion as we stand on Earth and what keeps us in that motion.  We move in a circular path as the Earth rotates  Gravity holds us to the Earth causing us to move in a circular motion

9. What does gravity do to our tangential speed?  Changes our direction of motion – but which direction?  Pulls us towards the center

10. If gravity was turned off, describe what would happen to all of us? Because we are moving with the Earth at the moment gravity turned off, we would continue at that velocity tangent to the surface of the Earth. ie. – we’d float away

11. What is centripetal acceleration?  Remember - acceleration is change in velocity  Centripetal acceleration – change in direction of tangential velocity towards the center of circular motion  Centripetal means “center seeking”

12. What causes centripetal acceleration? What is it? What does it do?  Centripetal force  Centripetal Force – a force that pulls an object into circular motion

13. In which direction does it act? Equation?  Always acts towards the center of a circle; thus “centripetal”  F c = m a c

14. Give some examples…  You give some examples…

15. While sitting in a swing, what causes you to move? What creates the centripetal force?  Applying a force to the swinger – a parent pushing a child  The chains on the swing pull the child into a curve

16. Why is it easier to swing on a rigid arm swing than a regular chained swing?  When swinging, a large amount of energy is used to keep the chains tight  The rigid bars transfer more energy into the swinging object

17. Explain how a washer removes much of the water from your clothes during its final spin cycle.  There is nothing to hold the water to the clothes – travels tangent to the circle made by the washer  The faster the washer spins, the faster the water travels out of the clothes

18. What exactly is the idea of “Centrifugal force”?  Centrifugal means “away from the center”  Examples of this situation?  When on the “Round-Up” ride, what happens to you?  You feel like you’re pushed against the wall of the ride  Pulled into circular motion by the wall Force applied by the wall on you You apply a force back on the wall

19. When your car turns in a curve, why do you “feel” as if you’re pushed in the opposite direction that your car is turning?  Because of Newton’s 1 st law, your body wants to keep moving in the direction its going until a force acts on it  it’s actually the car door pushing you into circular motion  What would happen if the door wasn’t there?  You’d fly out tangent to the curve!

21. Rotation of an object caused by a force

22. Is it easier to push a door open from the doorknob or from the center of the door? Why?  It takes less force to push from the doorknob than from the middle of the door  You generate more torque (or leverage) by pushing from the doorknob

23. What is torque? How do I create torque?  Torque is the tendency for an object to rotate about an axis  Create torque by pushing or pulling on an object perpendicular to it’s point of rotation

24. What does torque depend on? Equation?  The amount of force  Distance from axis of rotation  Angle of the force to the object being pushed  τ = (F)(r) sinθ

25. Examples of where you use torque in your daily lives…  Give me some examples…

26. Two kids are on a seesaw. Child A is twice as heavy as Child B. Could they balance the seesaw? How?  They need to make equal and opposite torque  If Child A is twice is heavy, then Child B needs to be at twice the distance.

27. Can you stand flat against a wall and touch your toes without falling over? Why or why not?  Try it…  No, because the torque from the weight of your upper body pulls downward without your legs underneath to support