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11
Kinematics of Kinematics of
Rigid BodiesRigid Bodies
Reference:Beer, Ferdinand P. et al, Vector Mechanics for Engineers : Dynamics, 8th Edition, Mc GrawHillHibbeler R.C., Engineering Mechanics: Dynamics, 11th Edition, Prentice Hall
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Introduction
• Classification of rigid body motions:
- general motion
- motion about a fixed point
- general plane motion
- rotation about a fixed axis
- curvilinear translation
- rectilinear translation
- translation:
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An example of bodies undergoing the three types of motion is shown in this mechanism.
C
E
A
D
B
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Translation
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Rotation About a Fixed Axis. Velocity
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Rotation About a Fixed Axis. Acceleration
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Rotation About a Fixed Axis.
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Equations Defining the Rotation of a Rigid Body About a Fixed Axis
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Given: Starting from rest when s = 0, pulley A (rA = 50 mm) is given a constant angular acceleration, αA = 6 rad/s2. Pulley C (rC = 150 mm) has an inner hub D (rD = 75 mm) which is fixed to C and turns with it.
Find: The speed of block B when it has risen s = 6 m.
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General Plane Motion
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Absolute and Relative Velocity in Plane Motion
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Absolute and Relative Velocity in Plane Motion
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Absolute and Relative Velocity in Plane Motion
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Sample Problem 15.2
The double gear rolls on the stationary lower rack: the velocity of its center is 1.2 m/s.
Determine (a) the angular velocity of the gear, and (b) the velocities of the upper rack R and point D of the gear.
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Sample Problem 15.3
The crank AB has a constant clockwise angular velocity of 2000 rpm.
For the crank position indicated, determine (a) the angular velocity of the connecting rod BD, and (b) the velocity of the piston P.
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Given: Block A is moving down at 2 m/s.
Find: The velocity of B at the instant θ = 45°.
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Given: Collar C is moving downward with a velocity of 2 m/s.
Find: The angular velocities of CB and AB at this instant.
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Instantaneous Center of Rotation in Plane Motion
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Instantaneous Center of Rotation in Plane Motion
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Sample Problem 15.4
The double gear rolls on the stationary lower rack: the velocity of its center is 1.2 m/s.
Determine (a) the angular velocity of the gear, and (b) the velocities of the upper rack R and point D of the gear.
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Sample Problem 15.5
The crank AB has a constant clockwise angular velocity of 2000 rpm.
For the crank position indicated, determine (a) the angular velocity of the connecting rod BD, and (b) the velocity of the piston P.
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Given: A linkage undergoing motion as shown. The velocity of the block, vD, is 3 m/s.
Find: The angular velocities of links AB and BD.
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Absolute and Relative Acceleration in Plane Motion
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Absolute and Relative Acceleration in Plane Motion
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Analysis of Plane Motion in Terms of a Parameter
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Sample Problem
The center of the double gear has a velocity and acceleration tothe right of 1.2 m/s and 3 m/s2, respectively. The lower rack is stationary.
Determine (a) the angular acceleration of the gear, and (b) the acceleration of points B, C, and D.
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Given: Point A on rod AB has an acceleration of 3 m/s2 and a velocity of 2 m/s at the instant the rod becomes horizontal.
Find: The angular acceleration of the rod at this instant.
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Given: The disk is rotating with ω = 3 rad/s, α = 8 rad/s2 at this instant.
Find: The acceleration at point B, and the angular velocity and acceleration of link AB.
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Sample Problem 15.7
Crank AG of the engine system has a constant clockwise angular velocity of 2000 rpm.
For the crank position shown, determine the angular acceleration of the connecting rod BD and the acceleration of point D.
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Sample Problem 15.7
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Sample Problem 15.8
In the position shown, crank AB has a constant angular velocity ω1 = 20 rad/s counterclockwise.
Determine the angular velocities and angular accelerations of the connecting rod BD and crank DE.
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Example Problems
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Homework
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