Week 5 - Friction, work, energy, power Flashcards
What are the three types of muscle action?
Isometric: force produced but no change in length
Concentric: force produced, shortens
Eccentric: force produced, lengthens
What is kinetic chain?
segmental links contributing to a movement
What is the difference between open and closed kinetic chain?
Open: distal end free to move in space eg kicking a soccer ball
Closed: distal segment fixed eg pushups
What are the positives and negatives of an open kinetic chain?
Positives -improve strength -improve ROM at a specific joint Negatives -increase shear forces -increase rotational forces -less functional
What are the positives and negatives of a closed kinetic chain?
Positives -works multiple muscles and joints -increase joint congruency -decrease shear forces -stimulates proprioceptors -more functional Negatives -increase muscle co-contraction -increase joint compressive forces
How would you maximise the velocity of a projectile?
- increase initial force
- increase angular velocity of segments
- increase ROM
- increase number of segments
- increase timing
What is the difference between skilled and unskilled people?
Unskilled: -small number of segments -distal segments don't lag back -'stiff' movements of joints -small ROM -lack sequencing Skilled: -large number of segments -segments lag and whip -'free' movements of joints -proximal --> distal sequencing -large ROM
What is friction?
force that arises when one body moves across the surface of another, measured in Newtons (N)
What is formula for friction?
friction co-efficient x normal force
What is normal force?
the force acting perpendicular to the surface, measured in Newtons
What does the friction co-efficient depend on?
nature of the surface, hardness, texture
Surface area and friction relationship?
friction is independent of surface area
What is the difference between dynamic and static friction?
Dynamic -kinetic/sliding friction -smaller than static friction Static -limiting friction -max friction generated before an object begins to move -force required to overcome inertia
What is mechanical work?
product of force and distance through which the force has moved an object, force applied to displace a body/object
What is the formula for work?
force x displacement
What is positive mechanical work?
- concentric contractions
- force and displacement in same direction
- object exerting the force is transferring energy to some other object
- eg throwing a ball, legs pushing off in a jump
What is negative mechanical work?
- force and displacement in opposite directions
- eccentric muscle contractions
- object is receiving/absorbing forces
- eg baseball catches a ball, legs do negative work when landing from a jump
What is power?
rate of work production/amount of work done over a period of time
What is the formula for power?
force x velocity
What is mechanical energy?
energy possessed by an object due to its motion or position
What are the two types of mechanical energy?
Kinetic and potential
Kinetic energy
-result from motion
-a moving object has the capacity to do work on another object due to its motion
KE = 1/2 x mass x velocity^2
What is the formula for kinetic energy?
KE = 1/2 x mass x velocity^2
Potential energy
-stored energy Gravitational -due to relative position of the earth Strain -due to deformities of an object -reform to return to original shape
Formula for gravitational potential energy
PE = mass x acceleration due to gravity x height
Formula for strain potential energy
SE = 1/2 x spring constant x distance material is deformed
