Chapter 7Circular Motion

Newton’s Laws of Universal Gravitation

Motion in Space

circular motion – when any object revolves about a single point (axis of rotation) tangential speed – the speed of an object in circular motion tangential speed (vt) depends on the distance of the object from the axis of rotation centripetal acceleration – the acceleration directed toward the center of a circular path (the word “centripetal” means “center seeking”) ac = vt

2/r (r = radius of the circular path) centripetal acceleration is due to change in direction tangential acceleration (at) is due to change in speed centripetal force – the net force of an object in uniform circular motion Fc = mvt

2/r (from Fc = mac) inertia is overcome by the centripetal force

Circular Motion Notes

Let’s try together:Page 235 Sample

Problem APage 237 Sample

Problem B

Try on your own:Page 236 Practice A

#2-4Page 238 Practice B

#1&2

~ one partner read pages 240 & 241~ one partner read pages 244 & 245~ one partner read pages 246 & 247~ each partner write down 3 important facts~ share and explain facts with each other

AGENDA:1)Review universal gravitation math2)Review universal gravitation concepts3)History of planetary motion

STUDY:1)Circular motion notes2)Circular motion math problems3)Universal gravitation notes4)Universal gravitation problems5)Planetary motion notes* Equations will be given

gravitational force – the mutual force of attraction between particles of matter Fg = Gm1m2

r2

the gravitational force and the mass of an object are directly proportional the gravitational force and the distance between the masses are indirectly proportional a gravitational force exists between ALL objects and attracts objects to one another high and low tides partly result from the difference between the gravitational force at Earth’s surface & at its center

Newton’s Law of Universal Gravitation Notes

A brief history lesson…In ancient times, people (including Plato and Aristotle) believed that Earth was at the center of the universe and the sun and other planets orbited Earth in perfect circles.

In the second century, Claudius Ptolemy theorized that planets travel in small circles while simultaneously orbiting Earth.

In 1543, Nicolaus Copernicus proposed that Earth and other planets orbit the sun in perfect circles.

A few years after Copernicus (and a generation before Newton’s law of universal gravitation), Johannes Kepler analyzed planetary motion and developed three laws of motion in space.

1) Each planet travels in an elliptical orbit around the sun.

2) An imaginary line drawn from the sun to any planet sweeps out equal areas in equal time intervals. Thus, planets travel faster when they are closer to the sun.

3) The square of a planet’s orbital period (T2) is proportional to the cube of the average distance (r3) between the planet and the sun. In other words, the time it takes for an object (ie: the moon) to revolve around another object (ie: Earth) is proportional to the distance between the two objects.

Kepler’s Laws of Motion in Space

BLACK HOLES!

A. Pair up with a group that researched a different topic.

B. Read paper aloud while other group follows along.

C. Answer the follow questions:1. Is the formatting correct (refer to the

rubric and the APA document on www.rushartsphysics.wikispaces.com)?

2. Is there an introduction, 3-5 body paragraphs, and a conclusion?

3. Do the introduction and conclusion paragraphs include the main ideas?

4. Is the grammar correct (remember: no “I”, “you”, etc.)?

5. Does the content make sense?6. Does anything sound too much like a

website)?7. Are there 5 references with 3 .edu and/or

.gov?D. Switch roles.E. Make changes.