1. Presentations (Those who did not present before break)
academic – Thursday 1/3
Welcome Back!
Physics Fun Fact
Presentations (Those who did not present before break)
Review Unit 4 PowerPoint
New Today:
Universal Law of Gravitation, Satellites in Orbit, Friction!
Formative (Finish for Homework!)
Unit 4 Test 1/11 (Friday)

2. Conceptual – Wednesday 1/2
Welcome Back!
Physics Fun Fact
Scott Kelly – Launch
Presentations (Those who did not present before break)
Review Unit 4 PowerPoint
New Today:
Universal Law of Gravitation & Satellites in Orbit
Begin Formative (Finish for Homework!)

5. Unit 4: Uniform Circular Motion

6. What is Circular Motion?
The motion of an object traveling on a circular path What does Uniform mean? Consider Rotation & Revolution

7. Uniform Circular motion
The motion of an object traveling at a constant (uniform) speed on a circular path.
Consider a constant radius as well

8. Period (T)
The time required to travel once around a circle, that is, to make one revolution
SI Unit: seconds [s]

9. Linear Speed vs. Tangential Speed vs. Rotational Speed
Linear Speed: How fast an object in a straight line.
Think about speed/velocity up to this point in the course
Tangential Speed: How fast an object moves along a circular path.
Ex) Spinning something on the end of a string in a circular motion
Rotational Speed: The number of rotations or revolutions per unit time.
Ex) Revolutions per minute (Car engine)

10. Velocity – [m/s]
Velocity of an object undergoing Uniform Circular Motion
Thought Question:
What is the direction of the Velocity vector of an object undergoing Uniform Circular Motion?

11. Centripetal

12. Centripetal acceleration
Units: [m/s2]
Example:
When you round a corner in a car, the car and its contents accelerate inward, towards the middle of the turn.

13. Centripetal Force
Force acting on an object undergoing circular motion, directed towards the axis of rotation.
Centrifugal Force is the fictitious force acting outward, away from the axis.

14. Banked Curves Tan ˆ = v2/rg
Banked curves are real world examples of uniform circular motion.
On roads, this allows drivers to negotiate turns are high rates of speed (for example, exiting a highway)
On racetracks, racers can travel at much higher rates of speed with an inclined racetrack.

15. Examples of Banked curves
Examples of Banked curves
Bill Nye Video:

16. Newton’s Law of universal gravitation
Every particle in the universe exerts an attractive force on every other particle.

17. Universal Gravitational Constant
G has the same value for all pairs of particles anywhere in the universe, no matter what their separation.

19. Satellites in circular orbits
Gravitational pull of the Earth provides the centripetal force required to keep an object in orbit around the Earth.
Satellites with a fixed radius will remain at a constant speed.

20. Orbital Speed of the Hubble Space Telescope
The Hubble Telescope orbits 598km (598 x 103m) above the Earth’s surface.
Determine the orbital speed of the telescope.
Known Values:
Radius of the Earth: 6.38 x 106m
Mass of the Earth: 5.98 x 1024kg
Answer: 7.56 x 103m/s

21. Friction & Uniform Circular Motion

22. Fc = μs mg = mv2/r Including Friction: Fc = μs FN = μs mg = mv2/r
Friction equations
Including Friction: Fc = μs FN = μs mg = mv2/r
μs - Coefficient of static friction (NO UNIT!)
Example:
Dry Road μs = 0.90
Icy Road μs = 0.10
Fc = μs mg = mv2/r