Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Introduction to general relativity wikipedia , lookup
Equivalence principle wikipedia , lookup
Coriolis force wikipedia , lookup
Electromagnetism wikipedia , lookup
Lorentz force wikipedia , lookup
Fictitious force wikipedia , lookup
Artificial gravity wikipedia , lookup
Centrifugal force wikipedia , lookup
Stuff you asked about: Derek DEREK TRUCKS RULES!!!!!!!!!!!!! A student riding in a train looks up and sees Einstein sitting next to him. Excited he asks, "Excuse me, professor. Does Boston stop at this train?“ I liked it when the guy said "It is what it has to be to do what it does". O rly? Also, I really like how you guys pick out certain comments to shown the class. Yes, they're funny, but they also show you're listening to the voice of the people even when you have so many students. A closer overview of the accelerating elevator problems would do fairly well, otherwise everything seems in check. Hope you have a wonderful day. I have always been terrifyingly horrible at questions involving tension. Can we please go over how other forces interact with it? Dearest instructor, on the second day of physics you won our love and admiration by shooting a monkey in the face with a dart gun. Since that spectacular event, you have carried out multiple demonstrations, but none have yet been as strikingly awe-inspiring as that first great spectacle. I hope that we can look forward to even greater performances in the future. So I can write anything here, and it might appear on the big screen on Tuesday? Every thing seems to make sense...which can be a good thing or a really bad thing. If one things for sure, it's that you must discuss the superiority that physics holds over the other sciences. Please clarify whether the "earth-moon" distance is the distance between their centers or surfaces Physics 211 Lecture 5 Today’s Concepts: a) Free Body Diagrams b) Force due to strings c) Force due to springs d) Force due to gravity Classical Mechanics I would like more free body diagram examples please. Free Body Diagrams 1)Choose system (object or group) 2)Draw forces acting on object -Gravity -Things touching (contact) T m mg Free Body Diagrams Free Body Diagrams Free Body Diagrams Tension Force Direction: Parallel to rope, always pulling. Magnitude: As much or little as needed for Fnet=ma T m mg Checkpoint BOX IN THE ELEVATOR A box of mass m is hung with a string from the ceiling of an elevator that is accelerating upward. Which of the following best describes the tension T in the string: A) T < mg B) T = mg C) T > mg The magnitude of the tension force must be greater than the magnitude of the weight force because the net force must be in the positive y direction if an acceleration exists in that direction. a Watch out for subtle mistakes… Many people got the right answer with explanations like this one: The downward force caused by gravity (with a negative acceleration) is added to the force caused by the upward acceleration. T m mg Remember: Net force causes acceleration a Tension Clicker Question A block weighing 4 lbs is hung from a rope attached to a scale. The scale is then attached to a wall and reads 4 lbs. What will the scale read when it is instead attached to another block weighing 4 lbs? ? m A) 0 lbs. m B) 4 lbs. m C) 8 lbs. Normal Force Normal force is the force perpendicular to the surface that prevents the objects from passing through each other. 1) Direction: Perpendicular to surface and out 2) Magnitude: As much or little required keep objects separate. "It is what it has to be to do what it does." This statement confused the hell out of me. Checkpoint A block sits at rest on a horizontal frictionless surface. Which of the following sketches most closely resembles the correct free body diagram for all forces acting on the block? Each arrow represents a force. A B C D The force of gravity on the box by the earth, and the normal force on the box by the floor. There are always forces on objects with mass, so C is not correct. The box is in equilibrium, so B is not correct and there are no forces to the right or left, so D is not correct. Clicker Question A block accelerates down a frictionless inclined plane. Which of the following sketches most closely resembles the correct free body diagram for all forces acting on the block? Each arrow represents a force. A B C - Gravity is down. - Normal is perpendicular to surface. D Spring Force Direction: Parallel to spring: Push or pull Magnitude:F=-kx Springs Example help with springs plzzzzzzzz A 5 kg mass is suspended from a spring with spring constant 25 N/m. How far is the spring stretched from its equilibrium position? F ma kx Mg 0 Mg 5*9.8 x k 25 A) 0.5 m B) 2 m C) 5 m Checkpoint A box of mass m is hung by a spring from the ceiling of an elevator. When the elevator is at rest the length of the spring is L = 1 m. If the elevator accelerates upward the length of the spring will be: A) L = 1 m B) L < 1 m C) L > 1 m a L m As the elevator accelerates upward, the spring's tension will be larger than the weight of the box, so the length of the spring is greater than 1m. Am I allowed to say common sense? Accelerating reference frames can confuse… The elevator accelerates upward and causes a force downward on the box (relative to the elevator). This means the spring will displace the box from equilibrium to a lower position relative to the elevator. the elevator is accelerating upward, that means that the mass of the object will get increasingly heavier (weight) because of the reactant force. a L m The box will have an additional force, ma, pulling it downward. This will expand the spring and cause its length to increase. Remember: Net force causes acceleration Clicker Question You are traveling on an elevator up the Sears tower. As you near the top floor and are slowing down, your acceleration A) is upward B) is downward C) is zero V a mg N Clicker Question You are traveling on an elevator up the Sears tower, and you are standing on a bathroom scale. As you near the top floor and are slowing down, the scale reads A) More than your usual weight B) Less than your usual weight C) Your usual weight a mg N Clicker Question A cart with mass m2 is connected to a mass m1 using a string that passes over a frictionless pulley, as shown below. The cart is held motionless. m2 The tension in the string is A) m1g B) m2g C) 0 m1 Clicker Question A cart with mass m2 is connected to a mass m1 using a string that passes over a frictionless pulley, as shown below. Initially, the cart is held motionless, but is then released and starts to accelerate. a m2 After the cart is released, the tension in the string is A) = m1g B) > m1g C) < m1g a m1 Universal Gravitation the slide about the earth+moon and the universal constant of gravity was confusing Direction: Toward other object (down near earth surface) Magnitude:F=GMm/r2 (mg near earth surface) Mm F G 2 r Near surface of earth r=Rearth F G Mearth m 2 Rearth 6.67 1011 m3 / kg s2 9.8 m / s2 m 5.97 1024 kg 6.4 10 m 6 2 m The slide in the pre-lecture talking about the value G was very confusing since it used so many equations and variables. I understand the general concept that any two objects always exert some kind of gravitational force on each other, but do not know how Newton came up with the specific values to fit the equations. So I guess this Newton guy knew his stuff.. There were a lot of equations shown in this lecture and I was wondering if you could discuss which ones we are going to be most focusing on. For example, will we need to combine the law of Universal gravitation with circular motion in order to solve for acceleration due to gravity? r Mm FGravity G 2 rˆ r Careful - r is measured from the center of Mars! r Fnet ma Mm v2 G 2 m r r v GM / r USE ALGEBRA! r d t v 2r t GM / r 3 r t 2 GM Careful, check units. Asks for time in hours, not seconds! r v GM / r r3 t 2 GM 3 1 r 2 t1 GM 3 t0 r0 2 GM 3/ 2 t1 r1 t0 r0 2/3 t1 r1 r0 t0 r