Linear Kinetics Biomechanics Exam 3 Study Guide

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LINEAR KINETICS

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38 Terms

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Newton’s 1st Law?
* Law of inertia
* A body remains at its current state of motion (constant velocity) unless acted upon by an external force
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What is inertia? Relationship between inertia and mass?
* Tendency of an object to keep the current state of motion
* Difficulty in changing the state of motion
* Inertia is proportional to mass of an object
* Mass=measure of inertia in linear motion
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Newton’s 2nd Law?
* Law of Acceleration
* An external force applied to a body causes acceleration
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F=ma? If F=0, what happens?
* Force= Mass/ Acceleration
* Acceleration= Force/Mass
* If force is equal to zero, then acceleration is zero because they are proportional to one another
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Meaning of Net Force
* Sum of all the forces acting
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Resistance vs. Propulsion
* Minimize friction as resistance
* Lubrication-synovial fluid (m=0.01)
* Skating - gliding
* Tire inflation & paving
* Maximize friction as source propulsion
* Source of horizontal GRF
* Cleats: prevent slipping
* Skating - push off
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Newton’s 3rd Law?
* Law of Reaction
* For every force (action), there is an equal and opposite reaction.
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What is reaction?
* Same magnitude
* Opposite direction
* EX:
* Bullet vs. Gun
* Fist Fighting
* Propulsion in swimming (pushing water behind you)
* Hockey players
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Ground Reaction Force (GRF)?
* Reaction supplied by the ground
* Passive force
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Importance of the GRF?
* Important for human motion
* Major external force that accelerates the body
* Speeds up
* Slows down
* The only external force one can voluntarily control
* Weight is always constant & downward
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How Does a high jumper utilize the GRF during takeoff?
* Slow-down of rightward (+) velocity
* Slow-down of downward (-) velocity
* Speed-up of upward (+) velocity
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Law of Gravitation?
* All bodies are attracted to one another due to their masses
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Properties of gravitation
* Proportional to masses
* Inversely proportional to (separation distance)^2
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Weight? Relationship between weight and mass?
* Gravity exerted to a body by the earth
* Weight= (mass)(gravitational acceleration)=mg
* Direction: downward
* Passes through the COM of the body
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Gravitational acceleration?
9\.81 m/s^2 in downward direction towards the earth
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Friction?
* Force acting at the are of contact between two surfaces
* Source of horizontal GRF
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Magnitude
* Proportional to
* Normal reaction force (N)
* Friction coefficient (WEIRD U)
* Cannot exceed your force
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Direction
* Opposite that of motion or motion tendency
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Friction Proporties
* Friction coefficient
* Force
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Sliding friction vs. Rolling friciton
* Sliding friction
* Friction due to relative motion of the surfaces
* Rolling friction
* Friction due to temporary deformations of the surfaces
* Sliding vs Rolling
* Sliding friction >> rolling friciton
* Beneficial to convert sliding to rolling for smaller friction
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Static friction vs Kinetic friction?
* Static friction
* Ff experienced with no motion (F=Ff)
* Max. static friction = force required to initiate motion
* Kinetic (dynamic) friction
* Ff experienced during motion (F>Ff)
* Force required to maintain motion once initiated
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Max static friction
* Max. static friction = force required to initiate motion
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Force required to initiate motion and force required to maintain the motion?
* Max. Static Friction: force required to initiate motion
* Kinetic (dynamic) Friction: Force required to maintain once initiated
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Your Force vs. Friction? Net Force?
* Force is a push or pulls acting on a body that causes a motion
* Net force is the sum of all the forces acting
* Friction is the force acting at the area of contact between 2 surfaces
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Lubrication vs. Friction? Role of synovial fluid in a synovial joint?
* Lubrication decreases friction. Synovial fluid reduces friction in the joints which in turn reduces injury between bones.
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Resistance vs. Source of propulsion
* Minimize friction as resistance
* Lubrication- synovial fluid (m = 0.01)
* Skating - gliding
* Tire inflation & paving
* Maximize friction as source of propulsion
* Source of horizontal GRF
* Cleats: prevent slipping
* Skating- push off
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Friction vs. Horizontal GRF
* Friction
* Force acting at the area of contact between 2 surfaces
* Source of horizontal GRF
* Used as a source of propulsion to MAXIMIZE friction
* Ex. Soccer Cleats, Ice skates
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Momentum? Its Importance?
* Amount of motion
* M=mv
* Vector
* Direction=direction of velocity
* Important in giving & receiving impact, collision etc.
* Unit: kg\*m/s
* Important in giving & receiving impact, collision, etc
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Principle of momentum conservation?
* If no external force, total momentum remains constant

\
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Impulse?
* The accumulated effect of force exertion over a period of time
* Vector quantity: direction= direction of force
* Unit: Ns
* Causes change in momentum
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Strategies in giving/ receiving impulse?
* Giving impulse (batting, throwing, etc)
* Maximize impulse by maximizing the momentum of the apparatus (batting)
* Elongating elapsed time
* Receiving impulse (landing, catching, etc)
* Reduce impulse, if possible
* Reduced impulse force/ pressure by increasing time/area
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Mechanical Work?
* Force applied against a resistance
* Accumulated effect of force exertion over a displacement
* Work = (force)(displacement)
* Scalar
* Unit: J (Joule) =Nm
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Positive work vs. Negative work
* Contribution vs taking away
* Determined by the angle between f &d
* If THETA > Pi/2 rad (opposite), negative work
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Muscle Contraction types vs Work?
* Concentric contraction: positive work
* Eccentric contraction: negative work
* Isometric contraction: no mechanical work
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Work while overcoming the gravity (weight): mountain or stair climbing?
* Mountain
* Stair Climbing
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Mechanical Power?
* Rate of work
* Intensity of work
* Rate of energy generation/consumption
* Power= (work)/(elapsed time)
* Power= (force)(velocity)
* Unit: W (Watt)= J/s
* Scalar
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Mechanical Energy? Potential vs Kinetic?
* Capacity to do mechanical work
* Mechanical energy (ME) = Potential E + Kinetic E
* Potential (PE): energy due to vertical (height)
* Kinetic (KE): energy due to motion (velocity)
* Scalar
* Unit: J
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Mechanical energy conservation? Diving ex?
* If gravity is the only external force acting on a system, ME remains constant
* EX: Diving (work causes a change in mechanical energy of the system
* Positive work: Increases energy of the system
* Negative work: Decrease energy of the system