Rotational Motion and Angular Momentum: Torque, Conservation, and Elasticity - Prof. Wolfg, Study notes of Physics

Various aspects of rotational motion, including torque, angular momentum, and conservation of angular momentum. It also introduces elasticity and elastic moduli, such as young's modulus, shear modulus, and bulk modulus. Students will learn about the relationships between torque, angular momentum, and elasticity, as well as the concepts of work and power in rotational motion.

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Pre 2010

Uploaded on 02/13/2009

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Phys141 – Wed 10/25
More on rotational motion (Chapters 10-
12)
Lab next week: conservation of angular
momentum
Add a person of
mass Mat a
distance dfrom the
base of the ladder
The higher the
person climbs…
Ladder Example, Extended
N
F
Example of static equilibrium
Tensegrity models
pf3
pf4
pf5

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Download Rotational Motion and Angular Momentum: Torque, Conservation, and Elasticity - Prof. Wolfg and more Study notes Physics in PDF only on Docsity!

Phys141 – Wed 10/

  • More on rotational motion (Chapters 10-
  • Lab next week: conservation of angular

momentum

  • Add a person of mass M at a distance d from the base of the ladder
  • The higher the person climbs…

Ladder Example, Extended

N

F

Example of static equilibrium

  • Tensegrity models

Torque and Angular Acceleration

  • Rotating mass m (along circle of radius r) tangential force F t

-> tangential acceleration: F (^) t = mat

Rotational motion description:

In general: Στ =Ια

2 t t t

a F r ma r mr I r

τ= = = = α

τ = I α

Angular Momentum

Angular momentum L relative to the origin O:

Cross product of the particle position r and linear momentum p

L = r x p

Angular Momentum of a Rotating Rigid Object

Each particle of the object rotates in the xy plane about the z axis with an angular speed of ω Angular momentum of an individual particle: Li = mi r (^) i^2 ω

Sum over all particles: 2 z i i i i i

L = ∑ L = ∑ m r ω = I ω

Work in Rotational Motion

Work done by F on the object as it rotates through an infinitesimal distance ds = r d θ dW = F.^ d s = ( F sin φ) r d θ dW = τ d θ

Note: Both work and torque have units of Nm – but remember: torque is not an energy!!

Power in Rotational Motion

  • The rate at which work is being done in a

time interval dt is

Power

dW d

dt dt

θ

Angular momentum of light can apply

torque on the microscale

Multiwalled Carbon nanotubes

Figure by Narupon Chattrapiban

Shape of Wavefront

Chapter 12.4: Elasticity

So far: We assumed that objects remain

rigid when external forces act on them

(except springs)

BUT: objects are deformable

  • It is possible to change the size and/or shape of the object by applying external forces

Elastic Moduli describe how materials respond to forces

Young’s Modulus

Measures: Resistance of a solid to a change in its length

A bar (surface area A) is stretched by an amount Δ L under the action of the force F

The tensile stress =

The tensile strain =

F

A

i

L

L

Young’s modulus:

tensile stress tensile strain i

F Y A L L

≡ = Δ

Shear Modulus

Measures: Resistance to relative motion of parallel planes within a solid

The shear stress =

The shear strain = shear stress shear strain

F

S A

x h

Shear modulus:

F

A

x h