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Things You Need to Know
- Objects that are moving in a circle behave under the rules of "circular motion".
- We'll be only looking at uniform circular motion. The magnitude of your velocity will remain constant (although the direction is always changing).
- Common formulas for this unit will be for centripetal velocity (vc), centripetal acceleration (ac), and centripetal force (Fc).
- vc and ac are under "Kinematics" in the formula booklet
- Fc isn't directly in your formula booklet, but it's mass (m) times ac.
- In circular motion, your centripetal force Fc will behave as your net force. In other words, it will equal the vector sum of all the other forces acting on the moving object in the circular motion system.
- In horizontal circular motion, Fc = Ff for objects moving on the ground, and Fc = FT (tension force) for objects tethered to a rope/string.
- In vertical circular motion, your Fc will equal FT + Fg at the top of the motion, and Fc will equal FT - Fg at the bottom of the motion.
- The FT will be minimized at the TOP of the motion.
- The FT will be maximized at the BOTTOM of the motion.
- Banked curves will always be frictionless in Physics 20, and can be solved with the formula:
- tanθ = v²/rg
- ...where θ is the angle of the slope, v is the velocity of the object moving on the banked curve, r is the bird's eye view radius of the turn, and g is the gravitational field strength.
- This is NOT on your formula sheet!
- ...where θ is the angle of the slope, v is the velocity of the object moving on the banked curve, r is the bird's eye view radius of the turn, and g is the gravitational field strength.
- tanθ = v²/rg
- Kepler's Laws describe planetary motion around the Sun, but also can describe the motion of moons around planets.
- First Law: “All planets in the solar system have elliptical orbits with the Sun at one focus.”
- Second Law: "Over equal lengths of time, a line from the Sun to the planet sweeps out equal areas.”
- Third Law: “The ratio of a planet’s orbital period squared over its orbital radius cubed is a constant. All objects orbiting the same focus (whether that focus is the Sun, a planet, etc.) will have the same constant (K).”
- K = Ta²/ra³ = Tb²/rb³
- This is NOT on your formula sheet!
- K = Ta²/ra³ = Tb²/rb³
- First Law: “All planets in the solar system have elliptical orbits with the Sun at one focus.”
- Satellite motion can be represented by recognizing that, in space, Fc = Fg
- Note that there are two different equations we can use for Fc depending on what we're given.
- Use the long formula for Fg every time: Fg = (Gm1m2)/r²
- Note that there are two different equations we can use for Fc depending on what we're given.
Homework Assignment
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