GV Conceptual Physics Ch. 11 Rotational Mechanics

Terms in this set (26)

Compare the effects of a force and a torque exerted on an object.
Force changes velocity and torque changes rotational speed.
How do clockwise and counter clockwise torques compare in a balanced system?
They are the same.
What is the law of inertia for rotation?
Objects in rotation stay rotating.
On what two quantities does rotational inertia depend?
The mass of the object and the distance of the radius from the axis.
Why is it easier to swing your legs back and forth when they are bent compared to keeping them straight?
By bending your legs, there is less rotational inertia because the mass is concentrated closer to the axis of rotation.
How can a person vary his or her rotational inertia?
By changing their body position, as when a dancer brings in his or her arms to spin faster.
What is Angular Momentum?
Product of rotational inertia and rotional velocity.
What is the Law of Conservation of Angular Momentum?
An object will maintain a constant AM unless acted by an unbalanced external torque.
What is the Lever Arm of a force?
The perpendicular distance between an axis and the line of action of a force that tends to produce rotation about that axis.
What is the formula for Linear Momentum?
This is the product of the mass and the velocity of an object.
Define Rotational Inertia.
It is the "reluctance" of an object to change it's state of rotation.
Distinguish between Rotational Velocity and Rotational Speed.
Rotational speed with a given direction is rotational velocity.
Define and give the formula for Torque.
Torque is the turning force that produces rotation. Torque equals force times lever arm.
In what direction should a force be applied to produce maximum torque?
For maximum rotation, the force should be applied perpendicular to the plane.
In terms of center of gravity, support base, and torque, why can't you stand with your heels and back to a wall and then bend over to touch your toes without falling over?
There must be a base of support beneath the center of gravity (CG). When the area bounded by your feet is not beneath your CG, there is a torque.
Where must a football be kicked so that it won't topple end over end as it sails though the air?
The ball must be kicked in the center so that the direction of force is through its CG; if it is kicked off center, in addition to the motion of the CG, the ball will also rotate about its CG.
What is the effect of adding a weight to the end of a baseball bat used for practice swings?
The added weight results in reducing its rotational inertia and this makes it easier to swing.
Which will have greater acceleration rolling down an incline: a large ball or a small ball?
Both have the same rotational inertia, therefore the same acceleration. Both will reach the bottom at the same time.
Which will have greater acceleration rolling down an incline: a hoop or a solid disk?
The disk will roll down with more acceleration than the hoop.
Distinguish between linear momentum and angular momentum.
Linear momentum is the inertia of motion, angular momentum is the inertia or rotation.
What motion does the torque produced by Earth's gravity impart to a vertically spinning bicycle wheel supported at only one end of its axle?
The pull of gravity that acts to topple the wheel causes it to precess in a circular path about a vertical axis.
When is angular momentum conserved?
If no unbalanced external torque acts on a rotating system, the angular momentum of that system is constant, or conserved.
If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her rate of spin increase?
The skaters speed will approximately double.
What happens to a gymnast's angular momentum when he changes his body configuration during a somersault? What happens to his rotational speed?
During a somersault, his mass is concentrated close to the axis because he is rotating about the CG. By tucking his body inward, he reduces his rotational inertia but increases his rotational speed.
What is rotational velocity?
Rotational speed together with a direction for the axis of rotation or revolution.
What are the 3 axes of rotation of the human body?
1-Logitudinal axis (from head to toe, most mass is concentrated along this axis, easiest for a skater to spin along this axis).
2-Transverse axis (from hip to hip, rotating as in a somersault).
3-Medial axis (front to back, as when doing a cartwheel).
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