Angular acceleration Definition and 566 Threads

In physics, angular acceleration refers to the time rate of change of angular velocity. As there are two types of angular velocity, namely spin angular velocity and orbital angular velocity, there are naturally also two types of angular acceleration, called spin angular acceleration and orbital angular acceleration respectively. Spin angular acceleration refers to the angular acceleration of a rigid body about its centre of rotation, and orbital angular acceleration refers to the angular acceleration of a point particle about a fixed origin.
Angular acceleration is measured in units of angle per unit time squared (which in SI units is radians per second squared), and is usually represented by the symbol alpha (α). In two dimensions, angular acceleration is a pseudoscalar whose sign is taken to be positive if the angular speed increases counterclockwise or decreases clockwise, and is taken to be negative if the angular speed increases clockwise or decreases counterclockwise. In three dimensions, angular acceleration is a pseudovector.For rigid bodies, angular acceleration must be caused by a net external torque. However, this is not so for non-rigid bodies: For example, a figure skater can speed up her rotation (thereby obtaining an angular acceleration) simply by contracting her arms and legs inwards, which involves no external torque.

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  1. P

    Angular Acceleration of Electric Motor

    Homework Statement An electric motor starts from rest at time t=0. Its angular velocity is: w=100t-4t3 A) If the angle of rotation, x, of the motor is also zero when t=o, determine an expression for this angle in terms of t. B) Determine the angular velocity when x=2pi radians. Give your...
  2. J

    Angular Acceleration Pulley: m,g,r,I

    Homework Statement A pulley has a radius of 2.70 m and a moment of inertia of 39.0 kg·m2. There is a hanging mass with a mass of 4.20 kg and it exerts a force tangent to the edge of the pulley. What is the angular acceleration of the pulley in rads/sec^2? r = 2.7m I=39kg·m2 m=4.2kg Homework...
  3. S

    Solving the Rod's Angular Acceleration Problem: Why and How?

    1. The problem: A Force F is provided at the top of a rod placed vertically placed on a smooth frictionless surface. The length of the rod is L and its mass, M. Find the angular acceleration of the rod at the instant the force is applied. - Please tell me how to solve this and why you...
  4. C

    What is the Moment of Inertia for a Falling Disc?

    Ok, so... \tau = \frac{dL}{dt} and L\equiv I\omega so \tau = \dot{I}\omega + I\dot{\omega} = \dot{I}\omega + I\alpha and i don't believe it'd be wrong to write (shouldn't be...right?) \alpha = \frac{\tau-\dot{I}\omega}{I} --- the situation I'm looking at is that of a disc (of radius 'R')...
  5. C

    Does angular acceleration not always come with torque?

    I always thought that torque = I*d²θ/dt² so that, if there is any d²θ/dt² on an object with a moment of inertia (both with respect to the same point)..then there must be a torque applied. However, I've found a case where this isn't true. So, I'm assuming there is more to it then that...
  6. J

    Angular acceleration and it's mass dependancy

    Homework Statement A wooden door is closed by applying a perpendicular force to it. If the magnitude of the force is constant and takes 2 seconds for the door to close, how long would it take to close the door with the same amount of force, in the same manner, if the door was made of a...
  7. Z

    Net torque Need help with angular acceleration.

    Homework Statement A certain wheel has a rotational inertia of 12 kg m2. As it turns through 5.0 rev its angular velocity increases from 5.0 rad/s to 6.0 rad/s. If the net torque is constant, its value is: Homework Equations Angular acceleration = dW/dT Net torque = (angular...
  8. R

    How Do You Calculate Constant Angular Acceleration?

    Homework Statement A rotating wheel requires 3.00 s to rotate 232.5 rads. It's angular velocity at the end of the 3.00 s interval is 98 rad/s. whatis the constant angular acceleration of the wheel? Homework Equations Not sure The Attempt at a Solution Is this question more complex...
  9. L

    Angular Acceleration Homework: Find Car Wheel Speed Change

    Homework Statement A motor car with wheels of 0.6,m diameter accelerates uniformly from 3 to 18m/s in 10 seconds. Find: a) the angular acceleration of the wheels b) the number of revolutions made by each wheel during the speed change Homework Equations A=v-u/t (angular equivilent with...
  10. F

    Angular acceleration of a solid uniform cylinder

    String is wrapped around the outer rim of a solid uniform cylinder that is free to rotate about a frictionless axle through its center. When the string is pulled with a force P tangent to the rim it gives the cylinder an angular acceleration alpha. If the cylinder had twice the radius, but...
  11. R

    Torque and Angular Acceleration

    The pulley shown in the illustration has a radius of 2.70 m and a moment of inertia of 39.0 kg∙m2. The hanging mass is 4.20 kg and it exerts a force tangent to the edge of the pulley. What is the angular acceleration of the pulley? All I have so far is the force exerted on the pulley by the...
  12. N

    What Power Is Needed To Accelerate An Object To 2.7 rad/s In 5.2 s?

    Homework Statement See the image attached What power must be applied to this object to accelerate it from rest to an angular speed of 2.7 rad/s in 5.2 s about the x axis? Homework Equations P = W / t - torque * angular velocity The Attempt at a Solution P = [(0.5 m)*(7...
  13. D

    Angular Acceleration of Wheels: Solve Homework Problem

    Homework Statement A cyclist starts from rest and pedals so that the wheels make 8.5 revolutions in the first 4.5 s. What is the angular acceleration of the wheels (assumed constant)? Homework Equations \alpha = \Delta\omega/ \Deltat The Attempt at a Solution I converted...
  14. K

    Angular Acceleration of a falling pole

    Homework Statement A 7.0m -tall electrical pole with mass 260 kg has a 42 kg electrical transformer attached to its very top. The pole is hit by lightning at its base, nearly severing the pole from its base. The pole begins to fall, rotating about the part still connected to the base...
  15. T

    Angular acceleration of a rod pivoted at an end, at angle below the horizontal

    Homework Statement The rod is at rest and is released, what is the angular acceleration immediately after release? The pivot is frictionless, gravity is 9.8 m/s^2. Homework Equations Icm = (1/12)ML^2 => Inertia at center of mass, this was given in the problem, i don't think it's necessary...
  16. R

    Angular acceleration of a pulley

    Homework Statement A 2.70 kg bucket is attached to a disk-shaped pulley of radius 0.141 m and mass 0.792 kg. If the bucket is allowed to fall, A- What is linear acceleration? B- What is angular acceleration? C- How far does the bucket drop in 1.5 s? Homework Equations a=g/(1+ (I/mr^2))...
  17. R

    Relation between angular acceleration of driveshaft and wheels

    Hi guys Can u tell me what is the relationship between angular acc. of driveshaft and that of wheel. Remember to include final drive ratio in relation.
  18. I

    Angular Acceleration with a Change in Rotational Axis

    Homework Statement A wheel spins at 45rpm with its spin axis vertical. After spinning 15 sec, it is spinning at 60rpm with its axis horizontal. Find its average angular acceleration and the angle the avg acceleration vector makes with the horizontal.Homework Equations Sorry, I can't really do...
  19. D

    Angular acceleration homework problem

    Homework Statement What is the tangential acceleration of a bug on the rim of a 8.0 in. diameter disk if the disk moves from rest to an angular speed of 75 revolutions per minute in 5.0 s? (b) When the disk is at its final speed, what is the tangential velocity of the bug? (c) One second...
  20. D

    Angular acceleration of a drill

    Homework Statement A dentist's drill starts from rest. After 2.90 s of constant angular acceleration it turns at a rate of 2.20 x 10^4 rev/min. (a) Find the drill's angular acceleration (in rad/sec^2). (b) Determine the angle (in radians) through which the drill rotates during this period...
  21. C

    Find its angular acceleration in radians per second per second

    A potter's wheel moves uniformly from rest to an angular speed of 0.23 rev/s in 29 s.
  22. T

    How Do You Calculate Time in Angular Motion Problems?

    Homework Statement A flywheel turns through 22 rev as it slows from an angular speed of 6.5 rad/s to a stop. (a) Assuming a constant angular acceleration, find the time for it to come to rest. (b) What is its angular acceleration? (c) How much time is required for it to complete the first 11...
  23. W

    Angular Acceleration Of A Wheel

    Homework Statement A wheel rotating with a constant angular acceleration turns through 22 revolutions during a 9 s time interval. Its angular velocity at the end of this interval is 15 rad/s. What is the angular acceleration of the wheel? Note that the initial angular velocity is not...
  24. T

    Angular Acceleration Problem Why am I not right?

    Homework Statement The blades in a blender rotate at a rate of 7900 rpm. When the motor is turned off during operation, the blades slow to rest in 4.0 s. What is the angular acceleration as the blades slow down? Vi= 7900 rpm = 82.72860654 rad/sec (This may be my error) Vf= 0 t= 4 secsHomework...
  25. C

    Angular Acceleration - What am I doing wrong?

    I am trying to answer the following question: A cyclist starts from rest and pedals such that the wheels of the bike have a constant angular acceleration. After 12.0 s, the wheels have made 26 revolutions. What is the angular acceleration of the wheels? My attempt at a solution: This...
  26. T

    Torque,flywheels and angular acceleration

    ive been trying to do this question all summer to no joy. I've got a flywheel in motion which then has a torque applied for short period and i need to find the angular acceleration. i know its something to do with inertia but I am completely lost cheers
  27. C

    Angular Acceleration of a Pulley

    Homework Statement A cable is around a pulley with: radius = 0.1 m moment of inertia = 0.15 kg * m(squared) The cable receives a pull of: force = 12 N Find the magnitude of the resulting angular acceleration of the puller. Homework Equations Average angular acceleration = Change...
  28. T

    Magnitude of Angular Acceleration

    Homework Statement A disk rotates with constant angular acceleration. The initial angular speed of the disk is 2π rad/s. After the disk rotates through 1π radians, the angular speed is 14π rad/s. What is the magnitude of the angular acceleration? Homework Equations w=w0+at The...
  29. M

    Angular Acceleration and Projectile Motion

    Homework Statement An amusement park game, shown in the figure (see attachment), launches a marble toward a small cup. The marble is placed directly on top of a spring-loaded wheel and held with a clamp. When released, the wheel spins around clockwise at constant angular acceleration...
  30. D

    Angular acceleration, is my method correct?

    Homework Statement A Pulley has mass M=4 kg and radius R=0.4 m. Assume that it is a uniform solid disk so that its moment of inertia is I= .5MR^2. A massless cord is wrapped around it and a tension force Ft is applied. The pulley starts from rest. After the tension force has been applied for...
  31. H

    Angular acceleration and angular velocity

    A child riding a merry-go-round is sitting on a horse onto a stationary pole 10m from the center of the merry-go-round. The ride starts from rest and with constant angular accleration obtains an angular velocity of 2 rad/s in 10 seconds. It then continues at 2 rad/s for 15 seconds and then...
  32. X

    Angular Acceleration, 2 Pulleys on common axle

    Note: This is similar to 2 previous questions I've seen here (https://www.physicsforums.com/showthread.php?t=261193"), and while this is my first post, I've lurked/found this site to really be helpful in getting me to be able to figure out how to solve problems I have with my physics homework...
  33. V

    Angular acceleration in revs/s^2

    http://img15.imageshack.us/img15/858/masteringf.jpg my attempt, \alpha= dw/dt 550-150 = 400 rev/min change 400/3.5 = 114 revs that wasn't right so i tried 114*60, which gives -6857 revs^-2 can someone help please? I'm not sure if I've got this whole revolution thing correct...
  34. J

    Simple angular acceleration problem

    Homework Statement A 4 meter long rod is hinged at one end. The rod is initially held in the horizontal position, and then released as the free end is allowed to fall. What is the angular acceleration as it is released? Homework Equations Ang. Accel. = (Tan. Accel.)/(radius) The...
  35. D

    Difficult: Linear vs. Angular acceleration

    Homework Statement A board of mass m and length L is hinged to the ground. Attached to the board is a cup of negligible mass and is positioned Rc away from the hinge. Also on the edge of the board a ball rests. When the board is dropped from an angle of theta the ball is meant to be...
  36. K

    Angular acceleration and speed

    Homework Statement A mass attached to a 43.9 cm long string starts from rest and is rotated 35 times in 57.0 s before reaching a final angular speed. Determine the angular acceleration of the mass, assuming that it is constant and determine the angular speed after 57 sec. Homework...
  37. Q

    When finding Angular Acceleration

    When finding Angular Acceleration, how is it that -7.129 x 10-4 rev/s2 equal to -4.47800 x 10-3 rad/sec2? In other words, how does the unit conversion work?
  38. M

    Understanding Angular Acceleration: Slowing Down in Clockwise Rotation

    Hello! May i ask a question? Why angular acceleration is positive if object rotating clockwise is slowing down? Thanks.
  39. S

    How Long Until a Pulsar Stops Rotating?

    Homework Statement A pulsar is a rapidly rotating neutron star that emits radio pulses with precise synchronization, there being one such pulse for each rotation of the star. The period T of rotation is found by measuring the time between pulses. At present, the pulsar in the central region of...
  40. H

    Angular Velocity and Angular Acceleration

    I feel really dumb, as this should be incredibly easy to figure out, but I keep getting the wrong answers. I am including the book's data so I can figure out how this needs to be done and then plug in my own values. Homework Statement Pilots can be tested for the stresses of flying...
  41. M

    Angular Acceleration of Rod w/ Pivoted Weight

    Homework Statement A uniform rod is pivoted at its center and a small weight of mass M = 5.07 kg is rigidly attached to one end. You may neglect the size of the weight and assume it is located right at the end of the rod. Homework Equations Now suppose that the rod has length L = 5.4 m...
  42. T

    What is the Angular Acceleration of a Rod Released From Rest at an Angle?

    Homework Statement A uniform rod with of weight of 10 kg and length of 5.8 m is pivoted at its center and a small weight of mass 5.15 kg is rigidly attached to one end. You may neglect the size of the weight and assume it is located right at the end of the rod. The system is released from rest...
  43. P

    Pivoting Rod (How to find angular acceleration)

    Homework Statement A uniform rod is pivoted at its center and a small weight of mass M = 5.07 kg is rigidly attached to one end. You may neglect the size of the weight and assume it is located right at the end of the rod. a) What vertical force, Fv, must be applied to the opposite end to...
  44. berkeman

    From Angular Velocity to Angular Acceleration - How?

    From Angular Velocity to Angular Acceleration -- How? Homework Statement Calculate the vector acceleration as a function of angle for a mass rotating in a circle at the end of a string. The mass is rotating in the vertical plane, in the counterclockwise direction. \hat{i} and...
  45. V

    Angular Acceleration: finding the coefficient of friction

    Homework Statement A car traveling on a flat (unbanked) circular track accelerates uniformly from rest with a tangential acceleration of 1.80 m/s2. The car makes it one quarter of the way around the circle before it skids off the track. Determine the coefficient of static friction between...
  46. V

    Angular Acceleration of a centrifuge

    A centrifuge in a medical laboratory rotates at an angular speed of 3400 rev/min. When switched off, it rotates 48.0 times before coming to rest. Find the constant angular acceleration of the centrifuge. Relevent equations: ωf = ωi + αt My work: I found out the time by (48 rev)(1min/3400...
  47. A

    A thought regarding angular acceleration, gravity, and weight.

    One of the first things we learn is that the Earth rotates very quickly (about once a day). We, as very imaginative 4/5/6 year old children, quickly realize the dangerous implications of this. However, as quickly as the fear beset us, we are calmed by our teacher/parent/television. "Gravity...
  48. S

    Solve for torque? Torque = Moment of Inertia * Angular Acceleration?

    I have a wheel with a diameter of 26 inches that weighs 3900 lbs that is spinning at 100 MPH... How much torque is needed to accelerate the wheel to 109 mph in 2.0 secondsanswer must be in ft-lbs convert any units as necessaryplease show me the math so I can learn how to do this..I have a few...
  49. D

    Angular acceleration of the pulley

    a block with a mass of m=10kg is connected to a pulley with a mass of M=2.5kg and a radius of R=0.5m. what is 1) the angular acceleration of the pulley 2) the acceleration of the block 3) the tension in the rope connecting them? ----------------------------------------------- equations...
  50. J

    Are angular displacement, angular velocity, and angular acceleration, vectors?

    This my first post on this very helpful forum. So are angular displacement, velocity, and acceleration actually vectors? My Physics book does not really give me a straight answer. Plus, if they are, why do they not have the classic vector notation of the arrow above \theta, \omega, and...
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