Chapter 7 PowerPoint Flashcards
(31 cards)
What is equilibrium?
Equilibrium: state achieved if the resultant force and net torque (moment) acting upon an object are equal to zero
Equilibrium can be either ____ or ____?
Equilibrium can be either linear or rotational
What is linear/translational equilibrium?
Linear or translational equilibrium: achieved when the net of the external forces acting upon a system is equal to zero
e.g., a tug-of-war
What is rotational equilibrium?
Rotational equilibrium: achieved when the net of the external torques (moments) acting upon a system is equal to zero
What is static equilibrium?
Defined as a system in linear and rotational equilibrium and possessing 0 linear or rotational velocity
The object is completely at rest
What three conditions must occur for static equilibrium to be acquired?
3 conditions occur for a static equilibrium state to be acquired
∑▒〖𝐹𝑦=0〗
∑▒〖𝐹𝑥=0〗
∑▒〖𝑇=0〗
Sums of all Vertical, Horizontal, and Torques are zero
What is dynamic equilibrium?
Don’t assume that because of 0 net force or Torque the object isn’t moving
Riding in an Elevator? Or Riding in a Car or Airplane?
Dynamic Equilibrium
A system in motion but it is experiencing no change in velocity or direction
What equations must be satisfied for dynamic equilibrium?
Dynamic equilibrium requires satisfying all of the following equations:
ΣFx - mαx = 0 ΣFY - mαY = 0 ΣFZ - mαZ = 0
ΣTx - Ixα x = 0 ΣTY - IYαY = 0 ΣTZ - IZαZ = 0
What is ΣF?
ΣF = the sum of the forces in a given direction
What is ma?
ma = the product of the body’s mass and acceleration
What is ΣT?
ΣT = the sum of the torques about the given axis
What is Iα?
Iα = the product of the body’s rotational inertia and angular acceleration about the given axis
What is stability?
Stability: the resistance of an object to having its equilibrium disturbed
The more stable the object, the more resistance it has against forces or torques that attempt to disrupt its equilibrium.
What is balance?
Balance: the ability to control the current state of equilibrium, and it implies conscious effort and coordination
Stability is more of a ____ term, whereas balance is a ____ reference?
Stability is more of a mechanical term, whereas balance is a neuromuscular reference
What is stable equilibrium?
Defined as a state in which a large force or torque is required to disrupt an object’s current position.
Note the Pyramid example
A lower center of gravity requires a longer torque to be applied to push the object over.
Coaching tip for most sports.
What is restorative force?
Restorative Force
Uses gravity to return the object to the original position
Gravity is a torque on the object.
Line of gravity still on the original side of the axis of rotation
What is a disruptive force?
Disruptive force
Force applied caused the line of gravity to move on the opposite side of the axis of rotation.
The more torque required to overcome the ____ ____, the more ____ the object is considered to be?
The more torque required to overcome the restorative torque, the more stable the object is considered to be.
What is unstable equilibrium?
State in which very little force or torque is required to disrupt an objects current position
Even a small force applied creates enough torque for the pyramid to fall over.
COG is not lifted at all, it only falls.
Pencil example
What is neutral equilibrium?
State in which an object has no tendency to fall in one direction or another.
Think of a Sphere
The only way to disrupt neutral equilibrium is by tilting the surface
What is linear stability?
Linear Stability – the resistance of a body to having its linear equilibrium disrupted.
Increased stability often accompanied by decreased ____?
Increased stability often accompanied by decreased mobility
What is a major factor of an object that determines its stability?
Mass of Object – major factor
Greater force required to linearly accelerate a more massive object
Greater mass leads to increase friction force
