Levers and Force Couples

Flashcards about levers and force couples, including lever types, mechanical advantage, and examples.

What is a lever?

A rigid bar, rod, or segment that rotates about a pivot point or fulcrum when acted upon by forces that produce rotation.

What is required for a lever system?

At least two linear forces each acting at a distance from the pivot point or axis.

What are the four variables in simple levers?

Muscle force/Effort (EF), Moment arm for the muscle force/Effort (EA), Resistance Force (RF), and Moment arm for the Resistance (RA).

Define Effort Force (EF).

The force generated by a muscle.

Define Effort Arm (EA).

The moment arm for the muscle force/Effort.

Define Resistance Force (RF).

Force in the form of gravity/external force/load pulling on segment/system.

Define Resistance Arm (RA).

The moment arm for the Resistance.

Describe a first class lever.

Forces are applied on opposite sides of the fulcrum or axis, with forces attempting to cause rotation in opposite directions.

In a first class lever, where is the fulcrum?

Between the effort force and the resistance force.

In what direction do the forces attempt to cause rotation in a first class lever?

Opposite Directions

Describe a second class lever.

The resistance force/load is between the effort force and the axis, with both forces acting at a distance from the same side of the axis.

In a second class lever, where is the resistance force?

Between the effort force and the axis.

What kind of lever is a second class lever?

Strength lever.

Describe a third class lever.

The effort force is between the resistance force/load and axis.

What kind of lever is a third class lever?

Fast (speed) lever.

In a third class lever, where is the effort force?

Between the resistance force and the axis.

What is the arrangement of elements in a first-class lever?

Load-Fulcrum-Effort

What is the arrangement of elements in a second-class lever?

Fulcrum-Load-Effort

What is the arrangement of elements in a third-class lever?

Load-Effort-Fulcrum

Give an example of a first-class lever.

Scissors

Give an example of a second-class lever.

Wheelbarrow

Give an example of a third-class lever.

Tweezers or Forceps

Give an example of a first-class lever in the body.

Raising your head off your chest.

Which joint acts as the fulcrum when raising your head off your chest?

Atlanto-occipital joint.

Give an example of a second-class lever in the body.

Standing on tip-toe.

Where is the effort exerted when someone stands on their tip-toes?

The calf muscles pulling upward on the heel.

Give an example of a third-class lever in the body.

Flexing the forearm by the biceps brachii muscle.

Define Mechanical Advantage (MAd).

Effort Arm (EA) / Resistance Arm (RA)

If MAd > 1.0, what has the advantage?

The internal (muscle) force has the advantage.

If MAd < 1.0, what has the advantage?

A larger amount of internal force is needed to overcome a smaller resistance - or - a small amount of external resistance can overcome a larger amount of internal force.

Forces acting together to move an object around a pivot point are called?

Force Couples

What muscles create a force couple?

Lower trapezius, Upper trapezius and Upper serratus anterior, Lower serratus anterior

Most joints are what class of levers?

Third Class Levers

In third class levers, which has the advantage?

Resistance

If you want to have the muscle work harder what do you do?

Increase RA (moment arm for resistance)

If you want to have the muscle work less what do you do?

Decrease RA (moment arm for resistance)

Where is the point of application for the reistance moment arm?

System CoM

Where does a therapist apply resistance to yield a greater torque?

Wrist

What does PNF stand for?

Proprioceptive Neuromuscular Facilitation

What mathematics are used in quantifying basic kinetics?

Calculations for 2D and 3D linear forces, moments, powers, etc.