machines in the body

Question 1

what is a torque?

Answer 1

• rotatory force when line of action doesn’t pass through the axis of rotation

Question 2

how is torque created?

Answer 2

torque (Nm) = force x momentum arm

Question 3

is a torque a vector or scalar?

Answer 3

• vector because has both magnitude and direction

Question 4

what is the moment arm?

Answer 4

• perpendicular distance from axis of rotation to line of force

Question 5

how do you calculate moment arm on free body diagram?

Answer 5

• trace line of action upwards and find 90 degree angle and trace it to the axis of rotation
• calculate from here

Question 6

what happens to moment arm when force is applied directly onto axis of rotation?

Answer 6

• moment arm would be zero so torque would be zero
• no rotatory force

Question 7

what is centric force?

Answer 7

• force directed through an object’s centre of gravity
• linear motion

Question 8

what is an eccentric force?

Answer 8

• external force not directed through an objects COG
• linear and angular motion

Question 9

what is a force couple?

Answer 9

• forces equal in size but opposite in direction on different lines

Question 10

describe difference between the directions of rotation on type of torque

Answer 10

clockwise = - torque
counter clockwise = + torque

Question 11

what are lever systems used for?

Answer 11

• used to generate toques onto joints and rotate our limbs

Question 12

what are the components of a lever?

Answer 12

• lever arm (bone)
• fulcrum or axis of rotation
• force of muscle
• resistance of body weight/ external force

Question 13

what is a lever?

Answer 13

• rigid bar that rotates about a fulcrum

Question 14

what is the effort force?

Answer 14

• muscle that acts to counteract any resistance force e.g. gravity

Question 15

where does muscle attachment insert ?

Answer 15

• at a point away from centre of joint so when muscles contract and pull on the bone a torque produced via eccentric

Question 16

what is the force arm?

Answer 16

• distance between force and axis of rotation

Question 17

what is the resistance arm?

Answer 17

• distance between the resistance and axis of rotation

Question 18

what is the mechanical advantage ?

Answer 18

• ratio of output force to input force
  MA= length of force arm/ resistance arm

Question 19

what is the MA of a lever with a longer force arm?

Answer 19

• value greater than one
• small movement at one point turns into large movement at another point

Question 20

what is the MA of a lever that has a longer resistance arm?

Answer 20

• less than one
• less torque from muscle force if its equal to same force of resistance

Question 21

describe the first class lever

Answer 21

• axis of rotation in the middle
  e.g. nodding your head
  R= skull weight; A= Atlanto- acciptial joint; F= neck muscles

Question 22

describe the second class lever

Answer 22

• resistance in the middle
  e.g. planter flexion
  A= 1st metatarsophalangeal joint; R= body weight; F= posterior calf muscles
• high mechanical advantage as force arm always greater than resistance arm

Question 23

describe the third class lever

Answer 23

• force in the middle
• most common lever
  -e.g. elbow flexion
  A= elbow joint; F= bicep brachii; R= weight of forearm

Question 24

what are third class levers designed for?

Answer 24

• producing speed and a wide ROM
  as force arm is shorter than resistance
• small change in length can create greater change at end of lever arm

Question 25

What is static equilibrium?

Answer 25

• both external forces and torques add up to 0

Question 26

what do isometric contractions mean?

Answer 26

• means that levers are in static equilibrium