MS Ch. 2 Study Guide PDF

⭐ 2.1 kinetics- Forces Kinetics a study of forces acting on a body Force a push or a pull that cause displacement Displacement motion of a body that occurs when a force is applied Force can either produce a rest, meaning stop or movement modification Force= mass x acceleration or f=m(a) Force has...

⭐ 2.1 kinetics- Forces Kinetics a study of forces acting on a body Force a push or a pull that cause displacement Displacement motion of a body that occurs when a force is applied Force can either produce a rest, meaning stop or movement modification Force= mass x acceleration or f=m(a) Force has 2 dimensions 1. Magnitude 2. Direction Magnitude is either weight or quantity Ex: dumbbell in hand ~5 pounds and you press overhead Magnitude is the same in each direction so it will result in equilibrium Ex: tug a war Types of forces 1. Gravity Most common 2. Muscles 3. Externally applied resistance Second most common 4. Friction Gravity weight of body segment Muscles provide force through a contraction, or stretch Externally applied resistance manual pushing Friction a resistance to movement bw two objects… could be good or bad Newtons Laws Newtons 1st law- inertia states that if a body is at rest, it will remain at rest and if a body is in uniform motion, it will remain in motion until an outside force acts upon it ex: a person pushing a box Newtons 2nd Law- Acceleration acceleration of an object depends on this mass of the object and the amount of force applied ex: a car accelerating Newtons 3rd law- Action-Reaction every action force, there is a reaction force in equal strength in the opposite direction ex: people pushing up against each other Summary: Kinetics is the study of forces on a body There are various types of forces Newton’s laws describe motion by inertia, force, and action-reaction 2.2 Forces & Vectors Load: force acting on the body • can deform or injure the body downward F ↓ *not all deformation = injury ex: picking up a box deformed annulus -11 I the body is meant to sustain a load - normal until injured = pathology - - -1111 Forces: can be internal or external internal force ex: muscle activation • muscle stretch • muscle contraction 6 types of Forces 1. compression - weight bearing 2. tension - pulling in opp ways 3. shear - ouch 4. torsion - twisting 5. bending 6. combination - most common Musculoskeletal forces 1. compression 2. tension 3. shear 4. torsion 5. bending 6. combination passive restraints: ligaments, joint capsules, connective tissue external force: gravity, body weight, free weight, resistance, physical contact (manual contact) higher magnitude vectors • line of application • direction of forces • each for has a magnitude lower magnitude resultant force: combining two vectors = new one vector forces w/ = magnitudes = equilibrium vector ex: tug of war point of application line of action Parallelogram Method pulls in 2 different directions creating a resultant force that is oblique 2.3 Levers Lever is a rigid bar that rotates around a fulcrum or an axis Levers have 3 elements: fulcrum (axis) force (effort) resistance (load) Levers also have 3 classes Class 1 axis(fulcrum) is in the middle Class 2 resistance “load” is closest to fulcrum Class 3 force “effort” is bw the fulcrum and load most common Note: the order of elements defines the class *FRE* From class 1-3 Class 1- fulcrum in the middle Class 2- resistance in middle Class 3- effort in middle effort = muscles 1st class lever 2nd class lever Point of resistance application lies bw the force and axis Muscle or internal force is greater than the external force 3rd Class lever *most common lever* External forces is greater than the internal (muscle) force how is external greater if biceps were able to create elbow flexion Review If axis is central: class 1 If resistance is central: class 2 If force is central: class 3 2.4 Moment & Torque Moment: force acting at a distance from a point of motion or from axis rotary moment force: biceps effort moment arm: lever arm in rotary force smaller moment arm = less difficulty lifting a force • can impact on muscle testing • designing an exercise • applying a technique torque: rotary motion at a joint • torque - creates motion! force applied around axis producing jt movement Torque = Force x Perpendicular distance from line of action fwd lean = torso shortens moment arm @ knees & lengthens moment arm @ hip hip dominant exercise Key takeaway: Longer moment/lever arm = more difficult 🧍 2.5 center of mass and angular velocity Center of Mass (COM) theoretical point around which the mass of an object is balanced - it is around S2 (It is also referred to a center of gravity (COG) * there’s a difference bw men and women Men have broader shoulders meaning COG would be more superior Women w broader hips, COG is going to be lower COM changes with movement Center of gravity Center of gravity is is thrown moved superiorly anterolaterally Motion COM will change w arm movement COM may be located outside of the body Base of support which is most advantageous? Small or large? -depends on the activity Bigger= stability Smaller= speed Wide base of support will help if you are doing something like lifting heavy weights Small base of support is better when having to do quick movements Note: assistive devices can help increase BOS Angular velocity rigid body rotating w respect to its center of rotation Moving the body segments at a high rate of angular velocity is a characteristic of skilled performance in many sports With inertia: if you keep the inertia close to the axis, we will move faster, also have faster angular velocity When extremities are extended, this slows down the motion and angular velocity, decreasing overall inertia Random note: Has the biggest impact on the body Force impacts movements and be altered by levers and rotary or linear displacement 2.6 Instrumentation force transducer: values & forces calculated through link segment modeling force = strain in instrument ex: force plate force plate: data related to ground reaction forces need data from pt • body mass • height • limb length 3D force vector ground reaction force (GRF) • find center of pressure on plantar aspect of foot • determine appropriate footwear • weight bearing precautions • amount sway F(y) - vertical, should go through belly F(x) - medial/lateral F(z) - anterior/posterior 2.7 Application pressure normal stress of joints: traction, normal traction compression as long as not in excess normal stress Pressure When provided over a large area helps disperse force Ex: person w a cast There is a large dispersive area of pressure in order to protect the joint Pulley: Torque magnitude of component greatest at 90 degrees change of lever arm will change force requirement Clinical: make easier movement by shortening lever arm! • knees flexed reduces force needed to lift legs Angular velocity Ex: ice skater pulling arms in to go faster By pulling in arms, they decrease the distribution of mass from the axis, reduces moment of inertia and increases angular velocity Ground Reaction Force : newtons 3rd law: action/reaction • foot produces a force against the ground • GRF changes in magnitude, dir, point of app through stance phase of • ground exerts = and opp force against the foot gait • biphasic