Chapter 11 rotational equilibrium

Chapter 11 Rotational Equilibrium
An Object will remain upright if its center of mass is above the area of support

Chapter 11 Key terms
Torque (p. 189) Torque is produced by this turning force and tends to produce rotational acceleration. Torque is different from force. To make an object turn or rotate, apply a torque.
Lever Arm (p. 190) When the force is perpendicular, the distance from the turning axis to the point of contact is called the lever arm.
Center of Mass ( p. 192) is where all the mass of an object can be considered to be concentrated.
Center of Gravity ( p. 195) Center of mass is often called center of gravity which is the average position of all the particles of weight that make up an Object

Chapter 11 Key Terms
Unstable Equilibrium (p.201)We say that an object balanced so that any displacement lowers its center of mass is in unstable Equilibrium.
Stable Equilibrium (p. 201) We say and object that is balanced so that any displacement raises its cent of mass is in stable equilibrium.
Neutral Equilibrium (p.201) An object that is balanced so that any small movement neither raises nor lowers it center of gravity is in neutral equilibrium.

11.1 Torque
To make an object turn or rotate, apply a torque
Torque is produced by a turning force and tends to produce rotational acceleration.
Force and torque are different; forces tend to make things accelerate whereas torque produce rotation.
A torque is produced when a force is applied with “leverage.” you use leverage when you use a screwdriver to open the lid of a paint can.
The lever arm is the distance from the turning axis to the point of contact
Torque can be calculated using the following equation: torque = force ┴ x lever arm

11.2 Balance Torques
When balanced torques act on an object, there is no change in rotation.
Children of unequal weight can balance on a seesaw by sitting at different distances from the pivot point.
Scale balance with sliding weights are based on balanced torques.

11.3 Center of Mass
The center of mass of and object is the point located at the object’s average position of mass.
The point where all of the mass of an object can be considered concentrated is called the center of mass.
Tor a symmetrical object, the center of mass is at the geometric center of the object. For irregularly shaped objects, the location of the center of mass varies.
Spin can be applied to and object by applying a force that does not pass through the object’s center of mass. Kicking a football in the middle, for example, will make it travel without rotating. Kicking the football above or below its center will make it rotate.

11.4 Center of gravity
For everyday objects, the center of gravity is the same as the center of mass.
The center of gravity, or CG, is the average position of all of the particles of weight that make up and object. For most objects on and near Earth, the terms center of mass and center of gravity are interchangeable.
If you throw a wrench so that it rotates as it moves through the air, you’ll see it wobble about its CG. The center of gravity itself would follow a parabolic path.
An object’s CG is its balance point; supporting the CG supports the entire object. A meter stick can be balanced by applying a force at its geometric midpoint-the location of its CG. Any object suspended at a single point will hang with its CGT directly below the point of suspension.

11.5 Torque and Center of Gravity
If the center of gravity of an object is above the area of support, the object will remain upright.
If the CG extends outside the area of support, an unbalanced torque exists, and the object will topple.
The Leaning Tower of Pisa does not topple because it CG does not extend beyond it base.
It is difficult to balance a broom upright in the palm of your hand because the support base is very small and far beneath the CG.

11.6 Center of gravity of people
The center of gravity of a person is not located in a fixed place, but depends on body orientation.
When you stand erect with your arms at your sides, your CG is within your body.
The CG is slightly lower in women than in men because women tend to be proportionally larger in the pelvis and smaller in the shoulders.
Raising your arms vertically over your head raises your CG by several centimeters.
When you stand, your CG is somewhere above your support base, which is the area bounded by your feet.

11.7 Stability
When an object is toppled, the center of gravity of that object is raised, lowered, or unchanged.
An object balanced so that any displacement lowers its center of mass is in unstable equilibrium.
An object balanced so that any displacement so that any displacement raises its center of mass is in stable equilibrium. Raising the CG of an object in stable equilibrium requires increasing the object’s potential energy, which requires work.
An object balanced so that any small movement neither raises nor lowers its center of gravity is in neutral equilibrium.
An object with a low CG is usually more stable than an object with a relatively high CG.

CONCEPT SUMMARY
To make an object turn or rotate, apply a torque.
When balanced torques acts on a object, there is no change in rotation.
The center of mass of an object is the point located at the object’s average position of mass.
For everyday objects, the center of gravity is the same as the center of mass.
If the CG of an object is above the area of support, the object will remain upright.
The CG of a person is not located in a fixed place, but depends on body orientation.
When an object is toppled, the CG of that object is raised, lowered, or unchanged.

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Chapter 11 rotational equilibrium

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