Week 5 - Friction, work, energy, power

Question 1

What are the three types of muscle action?

Answer 1

Isometric: force produced but no change in length
Concentric: force produced, shortens
Eccentric: force produced, lengthens

Question 2

What is kinetic chain?

Answer 2

segmental links contributing to a movement

Question 3

What is the difference between open and closed kinetic chain?

Answer 3

Open: distal end free to move in space eg kicking a soccer ball
Closed: distal segment fixed eg pushups

Question 4

What are the positives and negatives of an open kinetic chain?

Answer 4

Positives
-improve strength
-improve ROM at a specific joint
Negatives
-increase shear forces
-increase rotational forces
-less functional

Question 5

What are the positives and negatives of a closed kinetic chain?

Answer 5

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

Question 6

How would you maximise the velocity of a projectile?

Answer 6

• increase initial force
• increase angular velocity of segments
• increase ROM
• increase number of segments
• increase timing

Question 7

What is the difference between skilled and unskilled people?

Answer 7

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

Question 8

What is friction?

Answer 8

force that arises when one body moves across the surface of another, measured in Newtons (N)

Question 9

What is formula for friction?

Answer 9

friction co-efficient x normal force

Question 10

What is normal force?

Answer 10

the force acting perpendicular to the surface, measured in Newtons

Question 11

What does the friction co-efficient depend on?

Answer 11

nature of the surface, hardness, texture

Question 12

Surface area and friction relationship?

Answer 12

friction is independent of surface area

Question 13

What is the difference between dynamic and static friction?

Answer 13

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

Question 14

What is mechanical work?

Answer 14

product of force and distance through which the force has moved an object, force applied to displace a body/object

Question 15

What is the formula for work?

Answer 15

force x displacement

Question 16

What is positive mechanical work?

Answer 16

• 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

Question 17

What is negative mechanical work?

Answer 17

• 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

Question 18

What is power?

Answer 18

rate of work production/amount of work done over a period of time

Question 19

What is the formula for power?

Answer 19

force x velocity

Question 20

What is mechanical energy?

Answer 20

energy possessed by an object due to its motion or position

Question 21

What are the two types of mechanical energy?

Answer 21

Kinetic and potential

Question 22

Kinetic energy

Answer 22

-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

Question 23

What is the formula for kinetic energy?

Answer 23

KE = 1/2 x mass x velocity^2

Question 24

Potential energy

Answer 24

-stored energy
Gravitational
-due to relative position of the earth
Strain
-due to deformities of an object
-reform to return to original shape

Question 25

Formula for gravitational potential energy

Answer 25

PE = mass x acceleration due to gravity x height

Question 26

Formula for strain potential energy

Answer 26

SE = 1/2 x spring constant x distance material is deformed