2007-12-03 - Circular Motion
Today's nonsense
- Homework due Wednesday. pg. 142 #44-53 (omit 46c)
- Rehash of the "Moving on" rule: 10% has to get it in physics, and 10% doesn't have to get it in the calculus class.
- Item spotting rule: If you're in the class when the new item is put up on the wall, then you can't call it out unless you call it out at the end of the period, after everybody had a chance to call it. Furthermore, if you have already been in the class for one period (not a "visit"), then you are disqualified from making a claim on the new item.
- "There's no point in physics, but we treat it all as if there was."
- The story of Sir Cumference, and he was making pies.
- Learning: "you can't force it" <-- there's supposed to be something funny here.
- WE DO NOT LEAVE ANYBODY BEHIND IF THEY ARE TRYING.
a = v^(2) / r
v = 2 * pi * r / T in meters/second
Angular velocity would be in degrees/second.
T is the period , time required for one complete revolution.
Distance traveled during one period is 2 * pi * r.
Centripetal acceleration - acceleration of a particle moving with constant speed in a circle. It is directed radially inward toward the center of the circle.
Centripetal force - a net force in the direction of the acceleration to produce it. It is always directed inward, toward the center of the circle of motion. The centripetal force may be due to a string, spring, or other contact force.
Circular motion. The test grades are making more and more sense. Well there are many things you can try, try eating some starbusts or drinking some water, there are some things to work. Wednesday. It's online. The very homework that was half the test, yes. What goes around, .... and Brooke said it. That's omit 46c, so, oh, kind of like a circle. It all fits together. So you have the notes and now the notes are very simple. Let's talk about this acceleration and where this acceleration is when you are swinging something, what, pardon? Because someone said "I was printing the examples" and so I am going to go over it, and we're going to go over angular velocity if you don't know angular velocity and all that, velocity squared over the radius is your acceleration, and notice that this is not a magical formula, and 2 * pi * r is your circumference, so your period is 2 pi * r / V, and the period is the time required to complete one revolution.
Centripetal acceleration, that's what's going on when you're talking about it, so a car going around a circular ramp, we could talk about tops, or grades that don't exceed the number 73, who knows? It's directed radially inward toward the center of the circle, the force and acceleration are directed inwards. Whatever direction of the force, that's the same direction as acceleration. At any given time, the velocity is going to be tangental, and the acceleration is going to be inwards.
If vectors are perpendicular, they are orthogonal. The next calculus test is over AB material, like related rates. Ooh yes. And we are going to have some UT homeworks. It's back to back to back homework assignments.
Centripetal force is a net force. What can cause this? Angular velocity.
ex 1) A satellite moves at a constant speed in a circular orbit about the center of the earth and near the surface of the earth. If its acceleration is 9.81 m/s^2, find (a) its speed and (b) the time for one complete revolution.
Radius of the earth = r_(e) = 6378 km.
a = 9.81 = v^2 / r
v = sqrt(a * r)
v = 7910 m/sec = 7.910 km/sec
(b) The time for one complete revolution. V = 2 * pi * r / T.
T = 5066.265 seconds = 1.407 hr
ex 2) You swing a pail of water in a vertical circle of radius r. The speed of the pail is v_(t) at the top of the circle. (a) Find the force exerted on the water by the pail at the top of the circle. (b) Find the minimum value of v_(t) for the water to remain in the pail. (c) Find the force exerted by the pail on the water at the bottom of the circle, where the pail's speed is v_(b).
Tangental acceleration later?