# Forces and Mechanics

 Force and movement is used in our muscles, bones, and joint systems—many that act as _____.
 Levers
 Newton’s _____ law of motion• A body will stay at rest or in a state of uniform motion unless some force alters this behavior• Friction due to gravity is what stops the wheelchair/piano movement• In a car accident, nothing stops us from flying ahead accept airbag, seat belt, or windshield
 First
 Newton’s ______ law of motion• Acceleration of an object is proportional to the force applied to it• Force = mass times acceleration• F=m x a• a= acceleration > how fast speed increases or decreases• Ex: to move the piano (high mass) you have to push with a higher force relative to the wheelchair to get it to move (overcome inertia)
 Second
 Newton’s ______ law of motion• For every action, there is an equal and opposite reaction• Forces are balanced in objects as rest (or constant motion)
 Third
 Work done = ?
 force applied x distance moved
 A concept that an object’s entire weight (mass) can be represented as a SINGLE POINT in space [for physics analyses]
 Center of Gravity
 Medical Gravity: IV drip bags suspended above the patient
 Gravity provides the force to “push” solutions into veins (saline drips, blood transfusion, etc.), height related to drip rate of fluid
 Medical Gravity: Fluid drainage
 Must ensure that collection bag is below point of drainage from patient’s body as gravity pulls liquid “down”
 Medical Gravity: Raising a limb to reduce venous bleeding
 The heart has to pump against gravity, so the flow of blood is reduced upon elevation
 Medical Gravity: Improving blood circulation with a fainting patient
 Laying a person flat and raising their legs encourages blood flow to the patient’s brain, to keep oxygen flowing to this critical tissue/organ
 ______: • The force that opposes the sliding of two surfaces, one over the other• Due to surface imperfections between the surfaces• The reason we do not slip and fall when we walk
 Friction
 True or False: Dynamic friction is higher than static friction.
 False: Static friction is higher than dynamic friction– It is harder to start an object in motion than to continue its motion
 Give a few examples of how to reduce friction:
 • Use of lubricant oils, ball bearings, wheels, etc. are excellent ways to reduce friction when moving objects past/over one another• Highly polished surfaces have significantly lower friction as well
 Give some examples of how friction is reduced within/on the body
 • Mucus – In lungs, heart, and intestines• Saliva– Digesting foods• Synovial fluid reduces cartilage bone friction• KY jelly etc. for insertion of instruments and catheters in the body• Use of skin lotions/oils during massage
 _____ _____ are thought to result from sustained pressure on the skin causing restricted capillary blood flow beneath the skin > cell death > tissue ulceration– Keep the patient mobile to vary the point of contact with the bed– Use varied types of cushions, mattresses, and bedding– Goal is to relieve the prolonged pressure on the same points of contact
 Pressure Sores
 A _____ is a simple mechanical device that enables us to apply a force at one point and see an effect at another
 Lever
 The _____ is the pivot point of a lever
 fulcrum
 Lever Force Equation for movement
 The movement force is equal to the applied force times the distance from the pivot point
 _____- is formally the weight of the object desiring to be moved (as a force)—also called resistance sometimes
 _____- is formally the force needed to be applied to the lever to make the load move
 Effort
 Which class of lever is this: The load and efforton opposite sides of the fulcrum
 First class lever; a see-saw; the semispinalas capitis and the splenius capitis use the occipital condyles as a fulcrum to raise the from to of the head when they contract.
 What class of lever is this: The effort is outsidethe load on the sameside of the fulcrum
 Second-class; wheelbarrow; the quadriceps muscles of the anterior thigh elevate the knee when contracted. The hip joint is the fulcrum.
 What class of lever is this: The effort is insidethe load on the sameside of the fulcrum
 Third class; using a paddle, such as when paddling in a boat; when flexing the elbow, the biceps brachii muscle exerts an effort on the radius. the fulcrum is the elbow joint.
 Consider a human head sitting on top of the spine (previous slide). If the head weighs about 10lbs. and its COM is situated about 4” in front of the center of the spine, how much force would the muscles situated 1” behind the spine need to exert to keep the head from moving?
 – 4in. x 10lbs. = 40 in•lbs. = 1in. x (muscle force)– Muscle force = 40 in•lbs./ 1in. = 40lbs.
 Consider a human leg and foot (slide 17). If the leg/body weight exerted on the foot is about 40kg and its COM is situated about 10cm in back of the ball of the foot, how much force would the leg muscles situated 14cm behind ball of the foot need to exert to start to lift the foot off of the floor?
 – 40kg x 10cm = 400 kg •cm = 14cm x (muscle force)– Muscle force = 400 kg •cm / 14cm = 28.6kgNote: this is lower than the original force /weight due it being further from the fulcrum (the ball of the foot)
 _____ are used to change the direction of forces that we apply to help us do work
 Pulleys
 Pulleys help by adding _____ _____ in their use.