± Rigid-Body Motion

Learning Goal:

To be able to distinguish between a rigid body and a nonrigid body and to understand the types of rigid-body motion: translation, rotation, and general plane motion.

A rigid body is an idealized model of an object that does not deform or change shape. In reality, all objects deform as they move or as loads are applied to them; however, when this deformation is sufficiently small, we can approximate an object's motion by modeling it as a rigid body.

Part A

Classify each of the following items as a rigid body, a system of rigid bodies, or a nonrigid body: a fishing pole, a diving board, a mechanical spring, a bowling ball, a baseball bat, a system of gears, a slider block system, and a construction excavator's arm.

Drag the appropriate items to their respective bins.

 

 

Part B

Classify each of the following items by its type of motion: a bowling ball rolling down a bowling lane in a straight line; a system of gears in a winch as it winds; a slider block system including the links between each block; and a helicopter flying in a straight line without changing pitch, roll, or yaw (and for which you may neglect the rotation of the blades).

Drag the appropriate items to their respective bins.

 

The mechanism for a car window winder is shown below.

The crank gear C has radius r1 = 1.25 in , the spur gear attached at point B has radius r2 = 3.25 in , and the lift arms', AB and EF, length is l = 10.2 in . Lift arm AB is attached to the spur gear such that the two rotate together about point B. If the crank is turned with an angular velocity ωC = 0.250 rad/s , what is vw, the magnitude of the velocity of the window, vw, when the lift arms are at an angle θ = 16.0 ∘?

Express your answer numerically in inches per second to three significant figures.

vw =

0.943

in/s