Dynamics of Rotational Motion

Slides:



Advertisements
Similar presentations
Angular Quantities Correspondence between linear and rotational quantities:
Advertisements

Torque Rotational Equilibrium Rotational Dynamics
Warm-up: Centripetal Acceleration Practice
Dynamics of Rotational Motion
Chapter 9 Rotational Dynamics.
L24-s1,8 Physics 114 – Lecture 24 §8.5 Rotational Dynamics Now the physics of rotation Using Newton’s 2 nd Law, with a = r α gives F = m a = m r α τ =
Ch 9. Rotational Dynamics In pure translational motion, all points on an object travel on parallel paths. The most general motion is a combination of translation.
Review Chap. 10 Dynamics of Rotational Motion
Class 28 - Rolling, Torque and Angular Momentum Chapter 11 - Friday October 29th Reading: pages 275 thru 281 (chapter 11) in HRW Read and understand the.
Chapter 9 Rotational Dynamics.
Chapter 8 Rotational Equilibrium and Rotational Dynamics.
 Angular speed, acceleration  Rotational kinematics  Relation between rotational and translational quantities  Rotational kinetic energy  Torque 
Rotational Dynamics Chapter 9.
Chapter 11 Angular Momentum.
Dynamics of a Rigid Body
Chapter 10 Rotational Motion and Torque Angular Position, Velocity and Acceleration For a rigid rotating object a point P will rotate in a circle.
Chapter 12: Rolling, Torque and Angular Momentum.
Chapter 10: Rotation. Rotational Variables Radian Measure Angular Displacement Angular Velocity Angular Acceleration.
Phy 211: General Physics I Chapter 10: Rotation Lecture Notes.
Chapter Eight Rotational Dynamics Rotational Dynamics.
Chapter 11 Rolling, Torque, and Angular Momentum In this chapter we will cover the following topics: -Rolling of circular objects and its relationship.
Chapter 10 Rotational Motion
Physics 106: Mechanics Lecture 02
Halliday/Resnick/Walker Fundamentals of Physics 8th edition
Work Let us examine the work done by a torque applied to a system. This is a small amount of the total work done by a torque to move an object a small.
Angular Momentum of a Particle
Chapter 11 Angular Momentum.
 Torque: the ability of a force to cause a body to rotate about a particular axis.  Torque is also written as: Fl = Flsin = F l  Torque= force x.
Chapter 11 Angular Momentum. The Vector Product There are instances where the product of two vectors is another vector Earlier we saw where the product.
Chapters 10, 11 Rotation and angular momentum. Rotation of a rigid body We consider rotational motion of a rigid body about a fixed axis Rigid body rotates.
Rotation Rotational Variables Angular Vectors Linear and Angular Variables Rotational Kinetic Energy Rotational Inertia Parallel Axis Theorem Newton’s.
8.4. Newton’s Second Law for Rotational Motion
Chapter 9: Rotational Dynamics
Chapter 10 - Rotation Definitions: –Angular Displacement –Angular Speed and Velocity –Angular Acceleration –Relation to linear quantities Rolling Motion.
Chapter 10 Rotation.
Chapter 8 Rotational Motion.
When the axis of rotation is fixed, all particles move in a circle. Because the object is rigid, they move through the same angular displacement in the.
Equations for Projectile Motion
Chapter 8 Rotational Motion.
Rotational Mechanics. Rotary Motion Rotation about internal axis (spinning) Rate of rotation can be constant or variable Use angular variables to describe.
9.4. Newton’s Second Law for Rotational Motion A model airplane on a guideline has a mass m and is flying on a circle of radius r (top view). A net tangential.
Chapter 11 Angular Momentum. Angular momentum plays a key role in rotational dynamics. There is a principle of conservation of angular momentum.  In.
Rotational Kinetic Energy An object rotating about some axis with an angular speed, , has rotational kinetic energy even though it may not have.
Moment Of Inertia.
Chapter 9 Rotational Dynamics.
Thursday, Oct. 30, 2014PHYS , Fall 2014 Dr. Jaehoon Yu 1 PHYS 1443 – Section 004 Lecture #19 Thursday, Oct. 30, 2014 Dr. Jaehoon Yu Rolling Kinetic.
1 Rotation of a Rigid Body Readings: Chapter How can we characterize the acceleration during rotation? - translational acceleration and - angular.
1 Work in Rotational Motion Find the work done by a force on the object as it rotates through an infinitesimal distance ds = r d  The radial component.
Tuesday, June 26, 2007PHYS , Summer 2006 Dr. Jaehoon Yu 1 PHYS 1443 – Section 001 Lecture #15 Tuesday, June 26, 2007 Dr. Jaehoon Yu Rotational.
Chapter 11 Angular Momentum. The Vector Product and Torque The torque vector lies in a direction perpendicular to the plane formed by the position vector.
Wednesday, Nov. 10, 2004PHYS , Fall 2004 Dr. Jaehoon Yu 1 1.Moment of Inertia 2.Parallel Axis Theorem 3.Torque and Angular Acceleration 4.Rotational.
Rotational Motion – Dynamics AP Physics. Rotational and Translational Equalities Rotational Objects roll Inertia TORQUE Angular Acceleration Rotational.
Chapter 10 Lecture 18: Rotation of a Rigid Object about a Fixed Axis: II.
Today: (Ch. 8)  Rotational Motion.
1 7. Rotational motion In pure rotation every point of an object moves in a circle whose center lies on the axis of rotation (in translational motion the.
Rotational Dynamics The Action of Forces and Torques on Rigid Objects
1 Angular Momentum Chapter 11 © 2012, 2016 A. Dzyubenko © 2004, 2012 Brooks/Cole © 2004, 2012 Brooks/Cole Phys 221
PHYS 1443 – Section 001 Lecture #19
Goals for Chapter 10 To learn what is meant by torque
PHYS 1443 – Section 003 Lecture #18
Lecture Rigid Body Dynamics.
College Physics, 7th Edition
PHYS 1443 – Section 001 Lecture #14
Rotational Inertia and Torque
Rotational Dynamics Chapter 9.
Chapter 8 Rotational Motion
PHYS 1443 – Section 003 Lecture #15
Chapter 8 Rotational Motion.
Dynamics of Rotational Motion
PHYS 1443 – Section 003 Lecture #15
Presentation transcript:

Dynamics of Rotational Motion Chapter 10 Dynamics of Rotational Motion

Torque Definition: A force can be defined as something that causes linear motion to change. A torque can be similarly defined as something that causes a change in rotational motion.

The torque applied to a rigid body depends on the magnitude of the applied force, the distance away from the point of rotation ( lever arm), and the direction of the applied force. We can express the torque as a vector cross product.

Example The Achilles tendon of a person is exerting a force of magnitude 720 N on the heel at a point that is located 3.6 x 10-2 m away from the point of rotation. Determine the torque about the ankle (point of rotation). Assume the force is perpendicular to the radial arm.

Picture of foot and Achilles tendon 3.6 x 10 -2 m

Solution The magnitude of the torque is:

Torque and Angular Acceleration Consider a point on a rigid body. If a force is applied we can determine the tangential acceleration by Newton’s second law.

We can express this in terms of the angular acceleration by the following relation. The force on the particle can now be written as:

If we apply the definition of torque to our previous relation we get the following: We can use the vector triple cross product identity to rewrite this expression.

Vector Triple Cross Product

If we apply this identity to our product we get the following: However, r and a are perpendicular; therefore,

The torque now becomes: We can rewrite this in terms of the moment of inertia.

Rigid-Body Rotations About a Moving Axis Consider the motion of a wheel on an automobile as it moves along the road. Since the wheel is in motion it possesses kinetic energy of motion. However, since the wheel is both translating along the road and rotating, the kinetic energy of the wheel is shared between these two motions.

The kinetic energy of a rotating body about a moving axis is given by:

Example Determine the kinetic energy of a solid cylinder of radius R and mass M if it rolls without slipping.

Solution If an object rolls without slipping the speed of the center of mass is related to the angular speed by the following:

The kinetic energy is given by: The moment of inertia for a solid cylinder is:

The kinetic energy then becomes:

Work and Power for Rotations The work done rotating a rigid object through and infinitesimal angle about some axis is given by the following:

The total work done rotating the object from some initial angle to some final angle is:

If we examine the integrand we see that it can be rewritten as:

We integrate to get the work done.

Power The power of a rotating body can be obtained by differentiating the work.

If we differentiate we get:

Angular Momentum We define the linear moment of a system as: We saw that Newton’s second law can be written in terms of the linear momentum.

We can define momentum for rotations as well. We define the angular momentum of a system as: The value of the angular momentum depends upon the choice of origin. The units for angular momentum are:

Newton’s Second Law Suppose an object is subjected to a net torque. How does this affect the angular momentum?

Suppose the angular momentum changes with time. We can write the following:

Now suppose the mass is constant. When we differentiate we get:

The first term is equal to zero due to the properties of the cross product. Therefore, the change in angular momentum is:

Thus, we have Newton’s second law for rotations.

The angular momentum around a symmetry axis can be expressed in terms of the angular velocity.

If we take the time derivative of the angular momentum, once again we arrive at Newton’s second law.

Example A woman with mass 50-kg is standing on the rim of a large disk (a carousel) that is rotating at 0.50 rev/s about an axis through it center. The disk has mass 110-kg and a radius 4.0m. Calculate the magnitude of the total angular momentum of the woman plus disk system. Treat the woman as a point particle.

Solution The angular momentum of the system is: The magnitude of the angular momentum of the system is:

The magnitude of the linear momentum of the woman is: The magnitude of the angular momentum of the woman is:

The magnitude of the angular momentum of the disk is:

The magnitude of the total angular momentum of the system is:

The Conservation of Angular Momentum Consider a system with no net torque acting upon it. The equation above implies that if the net torque on a system is zero, then the angular momentum of the system will be constant.