week 6 lab 13,14,15,16 Flashcards
What is a lever?
A rigid bar that turns about an axis
In the body, the bones represent the bars and the joints are the axes.
What are the three parts of a lever?
- Force point
- Resistance point
- Fulcrum
What is the force point in a human body lever system?
The insertion point of the muscle of interest on a bone
What is the resistance point in a human body lever system?
The center of gravity of the moving body segment plus any external weight
Define the force arm (FA) of a lever.
The perpendicular distance from the fulcrum to the line of action of the force acting on the force point
Define the resistance arm (RA) of a lever.
The perpendicular distance from the fulcrum to the line of action of the resistance acting on the resistance point
Give an example of a first-class lever in the human body.
The triceps muscle acting at the elbow joint
What distinguishes second-class levers?
The resistance point is located between the force point and the fulcrum
What is a third-class lever?
A lever with its force point located between the resistance point and the fulcrum
What is the main advantage of third-class levers in the human body?
They permit speed and distance of movement at the sacrifice of force
What is the Principle of Levers?
A lever will balance when the product of the force times the distance from the point of application of the force to the fulcrum equals the resistance times the distance from the point of application of the resistance to the fulcrum
What does the equation F x FA = R x RA represent?
The balance condition of a lever
What is mechanical advantage (MA)?
The ratio between the force arm and the resistance arm of a lever
If the force arm is three times as long as the resistance arm, what is the mechanical advantage?
Three to one
True or False: Second-class levers are always force levers.
True
True or False: Third-class levers are always speed levers.
True
What is the center of gravity (CG)?
The point where the sum of all turning moments of the particles acting individually is exactly zero
How is the center of gravity defined in the human body?
- The point of intersection of the three cardinal planes
- The point of exact center around which the body may rotate freely
- The point around which the weight is equal on all opposite sides
What is the reaction board method used for?
Determining the center of gravity of the human body in any position when it is not moving
What equipment is typically used to measure the center of gravity?
- Reaction board
- Tape measure
- Accurate weighing scale
What is the significance of the angle of pull of the biceps muscle in calculations?
It simplifies calculations by allowing the assumption of a 90-degree angle
What must be done to balance a lever?
The product of force and force arm must equal the product of resistance and resistance arm
Fill in the blank: The force of gravity acts upon all particles in a given mass, resulting in a net effect considered as one acting at a point called the _______.
Center of gravity
What does it mean when the resistance arm is longer than the force arm?
The lever favors speed and range of motion at the sacrifice of force