Acceleration Definition and 1000 Threads

  1. S

    I Relativity and a Mirror

    If I park my space ship close to a highly-reflective mirror in space and then accelerate away from it at exactly 90 degress to its surface, how will the image I see of myself change as I approach the speed of light? best regards ... Stef
  2. R

    I Same old question, I still don't get it: E=1/2mv^2 - more E with V?

    I still don't get this and most answers all over kind of miss the point and just kind of recite without really explaining. Here's the dilemma. Yes, kinetic energy grows exponentially with speed. So a 1kg object changing from 0 to 1m/s increases by .5J. And from 4 to 5m/s increases from 8J to...
  3. S

    Dual Channel Network Acceleration on Android Phone

    My phone has a setting called Dual Channel Network Acceleration within the WiFi setup menu. Once you enable it, it shows a short list of apps that can be individually permitted to use this feature -- Firefox, Chrome, Internet (Native browser) and WhatsApp. I would like to know what this does...
  4. chwala

    What average power does the boy need to produce?

    In my approach, i have ##F_{Resolved} = 300 \cos 60^{\circ} = 150## Newtons. I also have, ... from ##v=u +at## ##2=0 +6a## ##a= \dfrac{1}{3}##. ##F=ma## ##F=30 ×\dfrac{1}{3} = 10## Newtons Therefore, ##P= \dfrac{(150+10) ×6}{6} = 160 ## W Insight is welcome...
  5. N

    Atwood's with a cylinder - Rotational Motion

    I am confused about three things: (i) To prove that accelerations are same, in the book it is given: ##mg−T=ma_1## (for the block) ##mg−T=ma_2## (for the cylinder) ##(a_1 = a_2 = a)## And thus the accelerations should be same. I can see that the same forces are acting on the bodies and that...
  6. A

    Constant acceleration problem: Dog chasing a surprised cat

    Here I'm not worried about the solution as I got it. There are two ways I could come up with: Either finding the time it takes the cat to leap through the window, use that time to find what distance does the dog cross through the room Or: finding both times, for the dog and the cat to cross the...
  7. M

    B Formula for time in terms of acceleration and distance

    Reading Griffiths book on electromagnetics I stumbled upon his analogy to Newton and acceleration. Author claims that the formula for time when acceleration and distance are given is: $$t= \sqrt{\frac{2\lambda}{a}}$$, all is clear beside 2 in the nominator. My calculations goes as follows: $$a =...
  8. S

    Acceleration of a ball at its max height after being thrown upwards

    The answer given is -10m/s2 because of constant downwards acceleration of gravity. i would like to know why is it not 0 at its peak height. at the top, velocity is momentarily 0, since acceleration is the change in velocity, change in 0 = 0. so why issn't a = 0? thanks
  9. S

    Kinematics, is this a poorly worded question?

    Like, i don't even understand what it means by the ball accelerating at 0.5m/s2. is it accelerating upwards constantly at 0.5m/s2? what about gravity? the answer given is weird. initial speed u = 5m/s and t = 10s it says time taken to go up is = time taken to go down. (why?) so total time...
  10. M

    B "Accelerations" as higher order derivatives

    In physics, velocity (speed) is the "change of position (spacial location) per change of time" and acceleration is the "change of velocity per change of time". Mathematically this is first and second derivative. Do further derivatives exist that correspont physical quantities like "change of...
  11. E

    Rolling without Slipping Demo

    So I'm watching this demo posted in another problem by @PeroK by Prof. Walter Lewin and I can't help but see that in the part where he is demonstrating the independence of acceleration cylinder length that the (presumably) shorter aluminum cylinder is edging out the win...Not intended, but...
  12. H

    A Acceleration in quantum mechanics

    Suppose in the presence of an electric field we solve electronic Hamiltonian with eigen energies and corresponding eigenstates ##|\psi\rangle##. The action of momentum operator on the stationary states ##|\psi\rangle## doesn't change by time. So, momentum-change (or acceleration) seems...
  13. N

    Block tied to a fixed string on an accelerating wedge

    So I basically identified two constraints, 1) The string cannot be slack, therefore the acceleration of block down the incline should be equal to the acceleration of the wedge. 2) The block must always stay in contact with the wedge. Hence, the acceleration of the block normal to incline must...
  14. I

    I The Universe is expanding with acceleration

    According to Hubble's law, galaxies are moving away from Earth at a speed proportional to their distance. In other words, the further away they are, the faster they move away from the Earth. The speed of galaxies is determined by their redshift. Based on this law, some scientists have come to...
  15. steff-23

    Relation between Friction, Velocity, and Acceleration

    For reference I'm a high school senior in physics. My thought process: 1) If the force of friction and applied force are equal the object "should" be at rest because the forces are equal (obviously this isn't correct because my professor tried explaining it and I'm not understanding the...
  16. Ediscoverlyf

    Angular velocity- A toy train rolls around a horizontal track

    30 rmp (2 pi) = 60 radians/minute = 1 revolution/sec 0 = 1revolution/s + angular acceleration (t) The only force acting on the toy train at this point is the force of friction. How do I use the coefficient of friction to find angular acceleration? Thank you so much in advance, I literally have...
  17. Z

    B Help me understand jerk of a falling object hitting an "ideal foam"

    I'm trying to calculate the theoretical minimum thickness of an "ideal foam" for a given jerk and acceleration limit. Say we have a ball in free fall from 1.83 meter, reaching 6 m/s. It then reaches an "ideal foam" for decelerating it. I'm trying to understand the connection between the...
  18. K

    Two spring-coupled masses in an electric field (one of the masses is charged)

    Here's what I've tried. First of all, I assume that q is positive. For particle A, then, I can write $$q E -k {\left( x _{A }-x _{B }\right) }=m \ddot{x }_{A }, $$ where ##x _{A } ## and ##x _{B } ## are the coordinates of the particles relative to their equilibrium positions from the point of...
  19. J

    I What causes an accelerated clock to record less events

    A clock is set up to continuously broadcast its indicated time via radio waves to non accelerating observers in different inertial frames of reference. The clock is accelerated and its tick rate is observed to decrease by all observers relative to the tick rates of their local clocks. Its...
  20. J

    I Symmetrical acceleration of Synchronised clocks

    If 2 synchronised clocks at the same location in space (away from any gravitational field) are equally accelerated away from each other and then equally accelerated back together to the original location will they then indicate the same time?
  21. cyap

    Concept of different accelerations on rotations of rigid bodies

    I don't seem to understand the difference of accelerations when a cord is wrapped around cylinders and spheres. What I was taught is that if the cord is wrapped around a cylinder/sphere, the acceleration of the cord and whatever it is connected to will be twice the acceleration of the cylinder...
  22. H

    Explain why applying different forces to objects of different masses result in different accelerations

    I don't really get why applying different forces to objects of different masses would result in different accelerations. I read my textbook, and I understand the formula F(net) = m*a, and I think the reason may be because mass is inversely proportional to acceleration ? But this doesn't really...
  23. H

    Why would this be accelerating positively?

    Above is a graph of the distance vs. time for car moving along a road. According the graph, at which of the following times would the automobile have been accelerating positively? OK, so I was able to get that at t=5 and t=29, it's accelerating positively (I graphed the velocity vs time graph...
  24. helloworld2941

    Confusion over acceleration of gravity as positive/negative

    okay I annotated the diagram given and the grey thing where they take y axis up as positive is what I understand to be, right? But in the answers, they start off by going V = u - gt. They've taken acceleration due to gravity as a negative value. Why? I thought the skateboarder was falling...
  25. danut

    Tension in a string which connects 3 pulleys

    I'm struggling to get to the correct answer, which I posted down bellow. The pulleys are ideal, so I figured that m₁ and m₂ will both move upwards (towards the ceiling?) with the acceleration a, while m₃ will move downwards with the acceleration -a. Let T be the tension in the string which...
  26. Heisenberg7

    Find the change in the time required, if acceleration increases by the differential amount 'da'

    According to the problem statement: $$a = \frac{dv}{dt} = const \implies dt = \frac{dv}{a} \implies \int_{0}^{T} \,dt = \frac{1}{a} \int_{0}^{v_f} \,dv \implies T = \frac{v_f}{a}$$ Now, the distance covered is given by, $$L = \int_{0}^{T} v \,dt \implies L = \frac{1}{a} \int_{0}^{v_f} v \,dv...
  27. I_Try_Math

    Analyzing acceleration of block on a ramp connected to a pulley

    Initially I thought a good strategy for solving the problem would be to find the torque on the pulley to get alpha (angular acceleration) and then use alpha to find the tangential acceleration of the pulley which is equal to the block's acceleration. I'm not sure if this is correct. Let ##...
  28. cianfa72

    I Fermi-Walker transport of proper acceleration along timelike congruence

    Hi, starting from a recent thread in this section, I decided to start a new thread about the following: Take a generic irrotational/zero vorticity timelike congruence. Do the 4-velocity and the direction of proper acceleration (i.e. the vector in that direction at each point with norm 1)...
  29. I

    B The inverse-square law: Gravitational force on two falling marbles

    Imagine making a hole in the ground, about a mile deep, with a large and square diameter. In the middle of the hole, there is a hollow and narrow tube with all air sucked out. Next to one of the walls, so close that it's touching, there is another hollow tube without air inside. Two identical...
  30. T

    Ball launched from a height of 5 meters --- Projectile motion

    I conceptually know how to solve this problem, what I struggle with is the direction of the acceleration. For example to solve the first question I need to find the horizontal displacement when the ball hits the ground. Therefore ##l_0= x(t_1)= x_0 + v_0 t_1##, where ##t_1## is the moment the...
  31. T

    Stretched spring attached to the center of a pure rolling disk

    I need to determine: 1) The initial acceleration of the disk 2) the speed of the disk when the spring reaches minimum displacement For point one I think I should use the free body diagram and then ##\Sigma F = ma##, I'm taking as positive the right and the upward directions and the counter...
  32. T

    Dynamics of a Block on top of a slab with friction between them

    I need to determine: 1) The accelerations of both the slab and the block, the moment right after the spring was released. => I can consider Fspring as a constant force. Both bodies can be considered as points of mass. I'm taking as positive the left direction. I've analyzed both objects using...
  33. chwala

    Find the magnitude of the child's acceleration

    In my working i have; For a) ##\tan 55^{\circ} = \dfrac{450}{R}## ##R = \dfrac{450}{\tan 55^{\circ} }= 315 N## part b) no problem here ...horizontal to left. c) This is where my real doubt is, i have using sine rule; ##\dfrac{9.8}{sin 55^{\circ} }= \dfrac{a}{sin 35^{\circ}}## ##a =...
  34. Isaac Hart

    B Formation of a black hole using acceleration

    Here is my question Imagine if you had an object, this object is then accelerated. The process of acceleration bends space-time. For a black hole to form there must be extreme curvature of spacetime. Therefore, accelerating an object at such a high rate could create a black hole. I am not...
  35. Z

    B Question About Dark Energy

    When there is an explosion, matter flies off in every direction. At first it is static, and then it accelerates, and keeps accelerating, until friction slows it down to a stop. In a vacuum would this matter continue to accelerate indefinitely? And could this be the cause of the continued...
  36. U

    AC gaussmeter in static magnetic field

    When you shake back and forth AC gaussmeter ,he significantly increase reading(magnetic field), because device is moved in Earth static magnetic field. Does his acceleration or velocity cause increase in reading and why he even increase reading if magnetic field from Earth is static and...
  37. P

    Kinematics: Acceleration of a figure skater changing direction

    My guess was simply that as acceleration changes from the north to east direction, the total magnitude change of v is ##v \sqrt 2##. Acceleration is ##\mu g##, so time would be ##\frac {v \sqrt 2} {\mu g}##. This agrees with the textbook solution. What I do not understand is the trajectory...
  38. A

    I Question Regarding Force Being Equal, Even Moving Upwards (if V=0)?

    I understand based on the equation F = ma that if there is no acceleration, the forces on the object all balance out to 0 in all directions. What I don't get is for example, slowly lowering a heavy stone slab at a constant velocity v, and raising it way above my head as high as I can at a...
  39. Owen Ploe

    Need help, to help, a friend with their HW (High School)

    This is the problem set. I am stuck from this point... If anyone could give me a hand I would really appreciate it. I know this is probably really simple, but I don't know any of this and have been trying my best with youtube, and other peoples posts. PS this is for high school
  40. tharindu_

    B Why don't cars accelerate according to F = ma?

    If the engine is constant, then the wheels of the car exerts a constant force on the floor. And F = ma, So the car should be accelerating rather than maintaining the same speed. What is going on here?
  41. Gargi

    Query related to Two-Dimensional Motion

    My initial approach to this question was breaking the components of acceleration in the x and y axes and applying the three equations of motion to find the final velocity as well as the final position. As we were expected to find the net final velocity of the particle, I found the resultant of...
  42. KukyZ

    How Much Vertical Acceleration Does a Jet Need to Avoid a Hill?

    The answer should be 10 m/s^2 but I don't know how to solve it
  43. M

    Friction - same direction as motion?

    Doesn't friction always oppose the motion? From the clockwise rotation here, shouldn't the cylinder be moving to the right? so why are the acceleration and friction in the same direction to the right, and in the same direction as the motion? (attached image for reference)
  44. Sam Jelly

    Center of mass acceleration for an inclined plane and mass m

    Why is the center of mass acceleration zero? Did I do anything wrong?
  45. hello478

    Arrow being fired to centre of target

    i solved it like this... s = ut + 1/2 at^2 t= 1.08 (from part a) u= 65 sin4.30 a= 9.81? or -9.81 the answer said -9.81 why? wouldn't acceleration change from -9.81 to +9.81 because it moves up then down??? its soo confusing...
  46. amandela

    Rolling Motion (Stone Gets Stuck in a Tire Going Forward)

    So I thought the stone would initially experience acceleration in the backward (leftward) direction then continually accelerate in the inward direction of the tire (i.e. upward then rightward then downward then leftward, etc.) as the tire moves forward. But the answer is immediately upward...
  47. MatinSAR

    If a rope is in free fall, does tension force act on it or not?

    This is the question. To this point everything is clear. I have problem with following part: The authors claim that each part of the remaining rope is under constant acceleration. So it is in free fall and only gravitional force acts on it. If we release a rope like above, before it hits the...
  48. I

    POWER - different approach, different results

    Basically, I tried to find the solution by calculating P=Fs/t, where F= 2250 and s is the distance traveled in the 12th second and that result differs from the result I get when I calculate the power using P=Fv. ##F=ma=1500*1.5=2250N## ##s_{12}-s_{11}=...
  49. amandela

    Work Done and Acceleration (Mistaken Answers?)

    So for Q1, I answered down (towards Earth) but the solution says there is no acceleration there. For Q2, I answered mgh, but the solution says it's mgh/t, which is power, right? I just want to make sure I'm not super confused. Thank you.
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