Lecture #4 (Work, Power, & Levers) Flashcards
What is work?
The product of force expended and the distance over which work is applied.
What is the formula for work?
W= Fs (work= force/displacement)
True or false:
The units for work are any combinations of force and distance (ex= foot/pounds)
True
What is a force that acts in the same direction as the object’s motion?
Positive force
What is a force that acts in the direction opposite to the object’s motion?
Negative force
What do levers need in order to work?
Torque
What is an example of negative work?
Deceleration
What is the rate at which work is done?
Power
What is the formula for power?
P= W/t (power= work/time)
What is the capacity to do work?
Energy
What is the law of conservation of energy?
The total amount of energy possessed by a body or an isolated system remains constant (it remains constant until a force acts upon it)
What is energy based on position? An example?
Potential energy; elasticity of muscles
What is the formula for potential energy?
PE=mgh (potential energy= mass x gravity x height)
What is energy based on motion?
Kinetic energy
What is the formula for kinetic energy?
KE= 1/2 mv^2 (kinetic energy= 1/2 x mass x velocity squared)
True or false:
The amount of work done is equal to the kinetic energy acquired.
True
What are the two sources of potential energy? What are they due to?
Gravitation (due to position on earth)
Strain (due to deformation such as elasticity)
Why do you have greater potential energy when your position on the earth is higher up?
The higher up you are, the more force that can be exerted resulting in increased work when resolution occurs
What are the five principles of rotary motion?
Torque (work of levers)
Summation of torques
Conservation of angular momentum (Newton’s laws)
Principles of levers
Transfer of angular momentum (segmental motion)
What are the three laws of rotation that are equivalent to Newton’s laws?
1) A body continues in a state or rest or rotation about its axis until an external force acts on it
2) The acceleration of a rotating body is directly proportional to the torque causing it, in the same direction as the torque, and is inversely proportional to the movement of inertia of the body
3) When a torque is applied by one body to another, the second body will exert an equal and opposite torque on the first
What is an example of the third law of conservation of rotation? (When a torque is applied by one body to another, the second body will exert an equal and opposite torque on the first)
Reverse muscle action
What is inertia?
A reluctance of an object to motion or a change in its motion
What are the four things inertia depends on?
- quantity of rotating mass
- the objects distribution around the axis of motion
True or false:
With the same speed of rotation, the farther you are from the axis, the less inertia you have.
False–the farther you are from the axis, the more inertia you have.
True or false:
Body position affects inertia. Why or why not?
True–this is because body position affects mass distribution (think of an ice skater with their arms out and then their arms in)
What is a change in angular acceleration that is directly proportional to the torque and inversely proportional to the moment of inertia
Rotary acceleration
What is the tendency to persist in rotary motion that is the product of moment of inertia and angular velocity?
Angular momentum
In lamen’s terms, what is rotary acceleration and angular momentum?
Rotary acceleration= how fast the angles are changing
Angular momentum= how long the force continues to exist
What is the conservation of angular momentum?
The total angular momentum of a body will remain constant unless acted upon by an external torque
What are simple machines that work to convert a force into a torque?
Levers
How many classes of levers are there? What “type” of lever is each? An muscular example of each?
3:
1= teeter totter (triceps)
2= wheelbarrow (brachioradialis with unweighted arm)
3= hammer? (biceps)
What is the benefit of a first class lever?
Redirection of force a change of direction of force
What is the benefit of a second class lever?
Smaller amount of force needed for heavy load (however, you sacrfice ROM for power)
What is the benefit of a third class lever?
A large effort force is applied to gain advantage of increased speed of movement and ROM
What is the most common lever in the body?
Class 3
True or false: Levers can change from class to class.
True–at least in the brachioradialis’ case. It can change from a class 2 to a class 3 when weight is added to the hand
What is the lever arm?
Portion of lever between fulcrum and force application
What is the effort arm (force arm)? The resistance arm (movement arm)?
Effort arm= perpendicular distance between fulcrum & line of pull
Movement arm= perpendicular distance between fulcrum and line of resistance
What is the turning effect of a rotary force?
Torque (the product of force magnitude and the length of the movement arm)
What is the angle in which levers are able to make the most amount of torque?
90 degrees
What is the angle of pull?
The angle between muscle insertion and the bone on which it inserts
In terms of angle of pull, what is the x and y axis?
X= mechanical axis of bone (parallel to lever-> non-rotary component) Y= perpendicular to mechanical axis of bone (perpendicular to the lever -> rotary component)
What angle of pull do most resting muscles have?
Less than 90 degrees
Where is the non-rotary force directed? The dislocating force? The rotary force?
Non-rotary=toward the fulcrum
Rotary= the moving limb
Dislocating force= away from fulcrum
What does an anatomical pulley do?
Changes the angle of pull of the muscle that is providing the force (this increase in angle of pull increases the rotary component)
What is an example of an anatomical pulley?
Patella, sesamoid bones
What is the perpendicular distance from the line of force to the axis of rotation?
Movement arm length
In the body, the weight of a segment cannot be altered instanteously. Because of this, how can we change torque of a segment that is due to a gravitational force?
Changing the length of the movement arm
True or false:
The sum of two or more torques may result in no motion, linear motion, or rotary motion.
True
An example of summation of torques would be?
Turning the steering wheel
What is the angle that is caused by resistance rather than the force of the muscle?
Angle of resistance (it’s the same thing as angle of pull except it’s outside the body)
