Body Definition and 1000 Threads

  1. LCSphysicist

    Black Body Entropy: Solving the Puzzle of q and N

    I thought that would be something like, using similar counts from Einstein solid, ##S = kln(\frac{(q+N-1)!}{q!(N-1)!})## Where q is ##hv## v is frequency But the results are not similar, so i am little stuck
  2. LCSphysicist

    Black Body Radiation: Facts & Overview

    I am really stuck at this question, i would appreciate any tips you have. I already try to goes with series but the calculation is getting harder and tiring, so probably this is not the right way.
  3. mastermechanic

    Rigid body kinetics -- force on ankle joint

    PROBLEM Here from the conservation of angular momentum I found angular velocity just before impact, $$ H_1 = 0 $$ $$ H_2 = I_0\omega + mV_0d $$ $$ H_2 = 66\omega + 76.(1.2).(0.87)$$ $$ H_1 = H_2 $$ $$ \omega = 1.202 rad/s $$ But I couldn't solve it to find joint force. Thanks in advance,
  4. patric44

    Using Matlab ode45 to solve a simple 2 body problem

    hi guys i am having some truble solving a simple 2body problem in MATLAB , basicaly i have a table of data that came from a simulation of a satellite orbiting the Earth with 1 min interval between them , i will only take the first inital position and velocity from that table and i sould...
  5. patric44

    Solving the two body problem in Matlab

    hi guys i am trying to code an algorithm for computing the trajectory of a basic two body problem situation according to the equation $$\ddot{r} = \frac{-\mu}{r^3} \vec{r}$$ i am trying to use the Euler method , but the problem is in converting this problem into a 3 separate equations one for...
  6. Ugnius

    Rotating body moment of inertia

    I have done some lab work , and now i have to answer some theoretical questions , but i can not find any data about this on the web or atleast i don't know where to search , i will add some pictures of experiment for you to better understand it. I was wondering can someone share their knowledge...
  7. R

    At what level is radiation totally safe for our body?

    According to this link https://www.sciencemag.org/news/2020/07/how-atomic-bomb-survivors-have-transformed-our-understanding-radiation-s-impacts even at radiation doses as low as 0.005 gray, there is still a risk of cancer over long term. I have read some Radiation Effects Research Foundation...
  8. Ugnius

    What is the origin of the minus sign in the derivatives of an oscillating body?

    I know it is a quite simple task. p = mv and F=ma. All i need to do is find the normal and double derivatives of s(t). But here's the problem , i have the answers and they state that first derivative is v = -Awcoswt and second is -Aw^2sinwt. Everything is quite clear to me, but I am wondering...
  9. T

    Forces on a body with vectors (IWTSE.org)

    I think I've made a mistake with the vectors. I was trying to get to the same point as the original working (made by IWTSE, not me), but one of the sides of a triangle can't be 0. I would appreciate some help.
  10. F

    Free body diagrams, coordinate systems origin/orientation

    Hello, When solving statics or dynamics problems, one important step is to draw the free body diagram (FBD) with all the external forces acting ON the system. The "chosen" system may be composed of a single or multiple entities. The external forces have components that must be projects on the...
  11. M

    What is the distance R between centers of mass in a barbell-shaped object?

    Normalizing respect m, M, R and k then the normalized force for the case of the bar bell body aligned with the direction of R become Fn = 1/(1+x)^2 + (1-x)^2 is a vectorial sum but in this case the vectors are aligned We can assume x<<1 but is not really material to the problem For...
  12. S

    Classical mechanics -- Equations for simulating the motion of a body

    Hello forum, i want to make a samulation of a body. The body will be moved horisontal on y,x axis. I want on my simulation the body to change direction many times(for example i want to go for 10sec right and then left end right...). My question is does i need more than one differential equation...
  13. S

    Rotating body viewed from its own rotating ref. frame, then perturbed

    Pondering over this thought experiment, a question comes to mind -- to which my brain sometimes replies "of course" and sometimes "no way!"A disk shaped satellite ("in zero-G") spins about its axis. There are two thrusters mounted as shown on two axial booms. The thrusters are fired briefly at...
  14. C

    Odd evolutionary outcomes: green fur, body fat, anything else?

    I was watching a grey squirrel the other day who stood out amongst green leaves, and wondered whether there was a reason no mammals have evolved green fur (AFAIK?)? I'm aware there are a couple who allow green algae to grow in their fur (sloth and polar bears). I mean we have weird things like...
  15. greg_rack

    How can the weight force of a rigid body be applied in a moments equation?

    I'm having a hard time solving this problem since I don't really know how to apply the weight force of the trap door. Ideally, in order to find the contact force exerted by the rod, I would find out the weight force of the trap in the point of contact and then find its component radial to the...
  16. Nathan M

    Understanding frequency calculations of an object (e.g human body)

    Apologies for the noob question. The frequency of the human body can be calculated based on weins law as follows: Wavelength = 0.002898/310 = 0.00000934838 m Plugging this into the equation λν = c we get frequency = 299792458 / 0.00000934838 = 32069 Ghz Elsewhere, I see that the resonant...
  17. Hamiltonian

    Does the tension in a string act on the body to which the pulley is attached?

    The normal reaction from the ground and from block m, the force of gravity are the forces I feel should act on the wedge but since the wedge is a perfectly rigid body and the pulley(which is massless) is attached to it so will tension also act on the wedge as well?
  18. Tony Hau

    B Can the human body affect a radio receiver?

    So I discover that a human body can affect a radio receiver. When I get close to a receiver, the radio produces buzz sound, which means that the radio signal is disturbed. However when I touch the plastic case of the receiver, the receive becomes normal. This phenomenon does not happen every...
  19. P

    I Size Limit of Accelerated Rigid Body in Irrotational Born Rigid Motion

    I was thinking - and reading a bit - about the size limit on accelerated frames, and there is an interesting and relevant result I found. If we rephrase the question from "is there a size limit on an accelerated frame" to "is there a size limit on an accelerated body in irrottational born...
  20. G

    Rigid body sliding without overturning

    My attempt: When the body is about to overturn backwards, the normal force and frictional force are applied on point A. If I want to avoid overturning, torque must be 0. Then, I calculate torque with respect to A. The value I get for h is negative, implying there is no minimum value for h...
  21. T

    What is the relationship between force, acceleration, and mass in a lift?

    Much like the previous question I've posted I was quite unsure of the the method I should take and resorted after many attempts to just trial and error which resulted in getting the correct answer of 5kg after dividing the weight of 70N by 14ms^-2 (sum of upward acceleration and gravitational...
  22. T

    Apparent weight of a body with upward acceleration

    I initially attempted to get the answer by multiplying the mass by 50, as I assumed if the upward acceleration was 5g then the weight could be found by just multiplying the mass by the acceleration of 50ms^-2. However that resulted in an answer of 3750 which was far below the correct answer of...
  23. K

    What was Newton's insight on rotational motion in Principia?

    mgR = d(mvR + MvR + ½M(R^2)v/R)/dt mgR = ma + Ma + ½Ma mg = a(m + 3/2M) v = mgt / (m+3/2M) My answer is incorrect. The right answer is v = mgt/(3m+M), but I have no idea what I'm doing wrong.
  24. S

    Think of a body which is at rest but not in equilibrium

    When a ball is thrown upward it becomes at rest at maximum height, at this it is not in equilibrium although it is at rest. It is not at equilibrium because force of gravity is acting on it? Still I cannot find good explanation from exam point of view.I also cannot find the figure/diagram.
  25. K

    What does it mean that a rigid body is in equilibrium?

    So I have always been thinking that equilibrium means that an object is not moving or having constant acceleration. On a webside they said: " A rigid body is in equilibrium when it is not undergoing a change in rotational or translational motion. " To me it sounds like the object then must not...
  26. S

    Free body Diagram of a Plank resting on two Cylinders

    I have put a picture of the problem above. The picture below shows my free body diagram. Fg is the component of the gravitational force in the direction fo the tangent at the point of contact and Ff is the frictional force between the plank and cylinder. I put Ff in the opposite direction as Fg...
  27. w4y021

    Can a Body Language Algorithm Reveal Our True Emotions?

    These days there is a question confuses me if it can be real or not. 2-3 years ago when I was looking around papers about computer sciences on the web, I came across to a sceintific paper which mentions an algorithm about analysing your language even it's a foreign language. So when you speak...
  28. Pushies

    CoM reduced by total body height when bending your knee X degrees

    Lets say that a man with a standing height of 185cm bent his knee 30 degrees, how many centimeters will be reduced from his standing height? Assume his femur length is 60cm and his tibia (shin) length is 50cm. Can anyone give me a hint? I've tried to use trigonometry but i don't think i fully...
  29. S

    How Can Music Videos Enhance Learning in High School Science Classes?

    I am a high school science teacher working on arts integration for thirty years in schools where many students have academic skills below grade level. I am looking for feedback.
  30. O

    Can we transfer the whole charge of a body to another body?

    When I asked "Can we transfer the whole charge of a body to another body?" my colleague replied: "If charged body (say 5 Coulomb) is any charged conductor ##A##, it can be done by enclosing ##A## completely by second uncharged conductor ##B## and connecting them by a conducting wire ##B## will...
  31. archaic

    Rigid body rotation problem: Mass on a cord spinning up a wheel on an axle

    (I know how to solve the problem, that's not what I am looking for.) I have a problem with how I ought to understand the moment of inertia. The only torque I see applicable on the wheel is that of the tension, and so I think that ##I## should be ##m_{\text{point}}R^2##, without including all the...
  32. LCSphysicist

    A body only rotates on an inclined plane if it has friction?

    I think that the answer probably will be yes, but i have a question: Well, with respect to center of mass that's right, but if i choose the axis passing through the contact point, the weight force will produce torque, even without the friction.
  33. Tony Hau

    How to derive the frequency for two body oscillatory motion

    Here is the diagram of the problem: and here is the answer of the question: What I don't understand is equation 1 and 2. The Hook's law states that F = -k(change in x) Why the change in x1 equals to x1-x2+l? x1-x2 equals to the length of the compressed spring. I cannot convince myself that...
  34. A

    Magnetic fields generated by the general rotations of a charged rigid body

    The calculations for the magnetic field produced by a uniformly rotating charged sphere can be found in basically every book on electrodynamics. I wonder what happen with the magnetic fields produced by rotating rigid solid that also present precession and nutation movements. The question comes...
  35. SilverSoldier

    Mathematically Modeling a Rolling Body with Slipping

    Basically, I want to know if my assumptions and workings are correct. This is how I see this situation. First, I'm viewing this body as a series of disconnected points, like I have in this animation I made, modeling purely rolling motion. Modeling the body like that worked in that case, and...
  36. T

    All the types of food and/or drinks that the body needs?

    Hi, Questions in the title. I figure it might be like the food pyramid that I learned in grade school however I am not sure and of course to save time by avoiding all the BS out there, I came to ask here as I have done in previous threads. by foods and drinks, I mean for example: protein, fiber...
  37. A

    Introductory application of the Newton Euler equations to a composite body

    α is the second derivative of angle and w is the first derivative In the free body diagrams the only force on A is the normal force since it is only constrained not to move vertically. Have I drawn the free body diagram and kinetic diagram correctly? By relating the accelerations of the...
  38. Adesh

    I How a rigid body causes a reaction force?

    The definition of rigid body says it cannot be deformed (theoretically). Now, Newton’s third law is caused (I mean the reaction force is caused ) due to the deformation of the body. What I have learned is that every body is like a spring, when we push on it we compress it and hence feel a...
  39. E

    Is the rotational KE of a rigid body considered as internal energy?

    I'm inclined to say no, but am by no means certain. The total kinetic energy of a system of particles is $$T = \sum_{i} \frac{1}{2} m_{i}\vec{v_i}\cdot\vec{v_i} = \frac{1}{2} m_{i}(\vec{v_{COM}} + \vec{v_{i}^{'}})^{2} = \frac{1}{2}M\vec{v_{COM}}^{2} + \frac{1}{2}\sum_{i} m_{i}...
  40. Adesh

    Analysis of a deformable body and Newton's 3rd Law

    I'm posting the images of "Sommerfeld's Lectures on Theoretical Physics, Vol 2, Mechanics of Deformable Bodies" I apologize for posting the images rather than writing out the whole thing. But I did it to so that nothing should be missed, as writing out the...
  41. E

    What is meant by "the body is on the point of ...." in mechanics?

    I see this sort of wording a lot, for instance, we might say that the block is on the point of slipping or the ball is on the point of leaving the surface of the hill. My guess is that it's to do with constraint forces; that is, at the exact point where the constraint forces acting on a body can...
  42. DarkMattrHole

    I Accelerating Body Creates Space-Time Curvature?

    If you are floating in space in your spaceship and you kick in the engines and accelerate at a comfortable 1G and you end up standing on the bottom of your ship, a slight curvature of space-time is formed, throughout the ship, perhaps immeasurable, such that without windows on the ship, you...
  43. Dr. Courtney

    The Human Body as a Dark Matter Detector

    https://www.sciencedirect.com/science/article/pii/S0370269320301040#br0210 I need to give this more thought, but the ballistics section is pretty good, and I think their basic dE/dx argument is sound: If a collision at a ballistic rate transfers about the same kinetic energy to the human body...
  44. brotherbobby

    Gauge pressure due to a floating body

    My answer : Both pressures are equal, i.e. ##\boxed{P_A = P_B}##. Reason : (1) The block of wood displaces an amount (mass) of liquid equal to its weight (archimedes' principle for floating bodies, or law of floatation). Hence we can imagine removing the block in the second case and filling it...
  45. C

    Temperature variations in body regions

    In thermal scanners in airports, subway, hospital and other stations to monitor the Coronavirus carriers. They point it at the foreheads, or is it the neck? We use home fever thermometers on our ears or armpits and not forehead. What are the variations of temperature in different parts of the...
  46. brotherbobby

    Apparent weight of body immersed in liquid

    I have to assume that ##h## is the height of the body. The graph above shows how the apparent weight of the body changes as it is immersed into the liquid. In (a), after immersing the whole height of the body, the apparent weight ##W_{\text{app}} > 0##. Hence the upthrust ##U < w_B \Rightarrow...
  47. carter7gindenv

    I Why is the black body spectrum bell shaped if it's absorptance is equal to 1?

    This bother me too much. A black body is said to absorb every incoming radiation. Looking at absorptance we have : A=Φabs/Φreceived So if a Black body absorbs everything we have A=1 Φ is a flux meaning object/time. This means that whatever the wavelength a black body will absorb the maximal...
  48. C

    Momentum conservation for a free-falling body in GR

    Hello everyone! It seems I can't solve this exercise and I don't know where I fail. By inserting the metric on the lefthand side of I. and employing the chain rule, the equation eventually reads (confirmed by my notes from the tutorial): $$m\frac{\mathrm{d}p_\delta}{\mathrm{d}t} =...
Back
Top