1. Home
  2. College physics
  3. Rotational motion and angular
  4. Angular acceleration

10.1 Angular acceleration  (Page 3/6)

<< Chapter < Page
  College physics     Page 3 / 6
Chapter >> Page >

So far, we have defined three rotational quantities— θ ,  ω size 12{θ,ω} {} , and α size 12{α} {} . These quantities are analogous to the translational quantities x ,  v size 12{x,v} {} , and a size 12{a} {} . [link] displays rotational quantities, the analogous translational quantities, and the relationships between them.

Rotational and translational quantities
Rotational Translational Relationship
θ size 12{θ} {} x size 12{x} {} θ = x r size 12{θ= { {x} over {r} } } {}
ω size 12{ω} {} v size 12{v} {} ω = v r size 12{ω= { {v} over {r} } } {}
α size 12{α} {} a size 12{a} {} α = a t r size 12{α= { {a rSub { size 8{t} } } over {r} } } {}

Making connections: take-home experiment

Sit down with your feet on the ground on a chair that rotates. Lift one of your legs such that it is unbent (straightened out). Using the other leg, begin to rotate yourself by pushing on the ground. Stop using your leg to push the ground but allow the chair to rotate. From the origin where you began, sketch the angle, angular velocity, and angular acceleration of your leg as a function of time in the form of three separate graphs. Estimate the magnitudes of these quantities.

Angular acceleration is a vector, having both magnitude and direction. How do we denote its magnitude and direction? Illustrate with an example.

The magnitude of angular acceleration is α size 12{α} {} and its most common units are rad/s 2 size 12{"rad/s" rSup { size 8{2} } } {} . The direction of angular acceleration along a fixed axis is denoted by a + or a – sign, just as the direction of linear acceleration in one dimension is denoted by a + or a – sign. For example, consider a gymnast doing a forward flip. Her angular momentum would be parallel to the mat and to her left. The magnitude of her angular acceleration would be proportional to her angular velocity (spin rate) and her moment of inertia about her spin axis.

Got questions? Get instant answers now!

Phet explorations: ladybug revolution

Join the ladybug in an exploration of rotational motion. Rotate the merry-go-round to change its angle, or choose a constant angular velocity or angular acceleration. Explore how circular motion relates to the bug's x,y position, velocity, and acceleration using vectors or graphs.

Ladybug Revolution

Section summary

  • Uniform circular motion is the motion with a constant angular velocity ω = Δ θ Δ t size 12{ω= { {Δθ} over {Δt} } } {} .
  • In non-uniform circular motion, the velocity changes with time and the rate of change of angular velocity (i.e. angular acceleration) is α = Δ ω Δ t size 12{α= { {Δω} over {Δt} } } {} .
  • Linear or tangential acceleration refers to changes in the magnitude of velocity but not its direction, given as a t = Δ v Δ t size 12{a rSub { size 8{t} } = { {Δv} over {Δt} } } {} .
  • For circular motion, note that v = rω size 12{v=rω} {} , so that
    a t = Δ rω Δ t . size 12{a rSub { size 8{t} } = { {Δ left (rω right )} over {Δt} } } {}
  • The radius r is constant for circular motion, and so Δ rω = r Δ ω size 12{Δ left (rω right )=rΔω} {} . Thus,
    a t = r Δ ω Δ t . size 12{a rSub { size 8{t} } =r { {Δω} over {Δt} } } {}
  • By definition, Δ ω / Δ t = α size 12{ {Δω} slash {Δt=α} } {} . Thus,
    a t = rα size 12{a rSub { size 8{t} } =rα} {}

    or

    α = a t r . size 12{α= { {a rSub { size 8{t} } } over {r} } } {}

Conceptual questions

Analogies exist between rotational and translational physical quantities. Identify the rotational term analogous to each of the following: acceleration, force, mass, work, translational kinetic energy, linear momentum, impulse.

Got questions? Get instant answers now!

Explain why centripetal acceleration changes the direction of velocity in circular motion but not its magnitude.

Got questions? Get instant answers now!

In circular motion, a tangential acceleration can change the magnitude of the velocity but not its direction. Explain your answer.

Got questions? Get instant answers now!

Suppose a piece of food is on the edge of a rotating microwave oven plate. Does it experience nonzero tangential acceleration, centripetal acceleration, or both when: (a) The plate starts to spin? (b) The plate rotates at constant angular velocity? (c) The plate slows to a halt?

Got questions? Get instant answers now!

Problems&Exercises

At its peak, a tornado is 60.0 m in diameter and carries 500 km/h winds. What is its angular velocity in revolutions per second?

ω = 0 . 737 rev/s size 12{ω= {underline {0 "." "737 rev/s"}} } {}

Got questions? Get instant answers now!

Integrated Concepts

An ultracentrifuge accelerates from rest to 100,000 rpm in 2.00 min. (a) What is its angular acceleration in rad/s 2 size 12{"rad/s" rSup { size 8{2} } } {} ? (b) What is the tangential acceleration of a point 9.50 cm from the axis of rotation? (c) What is the radial acceleration in m/s 2 size 12{"m/s" rSup { size 8{2} } } {} and multiples of g size 12{gs} {} of this point at full rpm?

Got questions? Get instant answers now!

Integrated Concepts

You have a grindstone (a disk) that is 90.0 kg, has a 0.340-m radius, and is turning at 90.0 rpm, and you press a steel axe against it with a radial force of 20.0 N. (a) Assuming the kinetic coefficient of friction between steel and stone is 0.20, calculate the angular acceleration of the grindstone. (b) How many turns will the stone make before coming to rest?

(a) − 0 . 26 rad/s 2 size 12{ - 0 "." "26 rad/s" rSup { size 8{2} } } {}

(b) 27 rev size 12{"27"`"rev"} {}

Got questions? Get instant answers now!

Unreasonable Results

You are told that a basketball player spins the ball with an angular acceleration of 100  rad/s 2 size 12{"100"``"rad/s" rSup { size 8{2} } } {} . (a) What is the ball’s final angular velocity if the ball starts from rest and the acceleration lasts 2.00 s? (b) What is unreasonable about the result? (c) Which premises are unreasonable or inconsistent?

Got questions? Get instant answers now!

Questions & Answers

if three forces F1.f2 .f3 act at a point on a Cartesian plane in the daigram .....so if the question says write down the x and y components ..... I really don't understand
Syamthanda Reply
hey , can you please explain oxidation reaction & redox ?
Boitumelo Reply
hey , can you please explain oxidation reaction and redox ?
Boitumelo
for grade 12 or grade 11?
Sibulele
the value of V1 and V2
Tumelo Reply
advantages of electrons in a circuit
Rethabile Reply
we're do you find electromagnetism past papers
Ntombifuthi
what a normal force
Tholulwazi Reply
it is the force or component of the force that the surface exert on an object incontact with it and which acts perpendicular to the surface
Sihle
what is physics?
Petrus Reply
what is the half reaction of Potassium and chlorine
Anna Reply
how to calculate coefficient of static friction
Lisa Reply
how to calculate static friction
Lisa
How to calculate a current
Tumelo
how to calculate the magnitude of horizontal component of the applied force
Mogano
How to calculate force
Monambi
a structure of a thermocouple used to measure inner temperature
Anna Reply
a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4
Amahle Reply
How is energy being used in bonding?
Raymond Reply
what is acceleration
Syamthanda Reply
a rate of change in velocity of an object whith respect to time
Khuthadzo
how can we find the moment of torque of a circular object
Kidist
Acceleration is a rate of change in velocity.
Justice
t =r×f
Khuthadzo
how to calculate tension by substitution
Precious Reply
hi
Shongi
hi
Leago
use fnet method. how many obects are being calculated ?
Khuthadzo
khuthadzo hii
Hulisani
how to calculate acceleration and tension force
Lungile Reply
you use Fnet equals ma , newtoms second law formula
Masego
please help me with vectors in two dimensions
Mulaudzi Reply
how to calculate normal force
Mulaudzi
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
<< Chapter < Page Page > Chapter >>
Practice Key Terms 3

Read also:

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?

Ask