5 - Biomechanical principles and levers

Question 1

what is Newton’s first law?

Answer 1

the law of inertia
- when a force is required to change the state of motion

example: the ball will remain at rest on the penalty spot until someone kicks it - a force is applied

Question 2

what is Newton’s second law?

Answer 2

the law of acceleration

• f = ma
• the magnitude and direction of the force determines the magnitude and direction of the acceleration

example: greater the force applied, the greater the acceleration of the ball (further and faster it will go)

Question 3

what is Newton’s third law?

Answer 3

law of action/reaction
- for every action (force) there is an equal and opposite reaction (force)

example: when a footballer jumps for a header, there is a force exerted on the ground to get height and the ground exerts an upward force (equal and opposite) upon the player

Question 4

what is linear motion?

Answer 4

motion in a straight or curved line, with all body parts moving the same distance at the same speed in the same direction

Question 5

what is angular motion?

Answer 5

movement of a body or a body part in a circular path about an axis of rotation

Question 6

what is a scalar and vector?

Answer 6

scalar quantity: measurement described in terms of their magnitude
- e.g: speed and mass

vector quantity: measurement described in terms of their magnitude and direction
- e.g: acceleration, force, velocity etc.

Question 7

what is the equation for speed?

Answer 7

s= d/ t

• s in m/s
• d = m
• t = s

Question 8

what is the position of the centre of mass?

Answer 8

it is the point of balance

Question 9

what is the line of gravity?

Answer 9

the line extending vertically downwards from the centre of mass

Question 10

what is the base of support?

Answer 10

the larger the area, the greater the stability

- e.g: wide stance of a boxer

Question 11

what factors affect stability?

Answer 11

• height of the centre of mass: lowering the centre of mass increases the stability
• position of the line of gravity: should be central over the base of support (increases stability)
• area of the support base: larger the base, more stable they are.
• mass of the performer: greater the mass, increased stability (due to increased inertia)

Question 12

what is inertia?

Answer 12

the resistance an object has to a change in its state of motion

Question 13

what is the fulcrum?

Answer 13

the point about which the lever rotates

Question 14

what is the resistance (load)?

Answer 14

the weight to be moved by the lever system

Question 15

what is the effort?

Answer 15

the force applied by the user (muscle) of the lever system

Question 16

apply the three components of the lever system to our musculoskeletal system.

Answer 16

fulcrum = joints 
resistance = weight of body part being moved 
effort = muscles 

(bones act as levers)

Question 17

how do we classify levers?

Answer 17

first (F)
second (L)
third (E)

Question 18

what is the first class lever?

Answer 18

when the fulcrum lies between the effort and resistance

e.g: extension of elbow

Question 19

what is the second class lever?

Answer 19

when the resistance is between the fulcrum and effort

e.g: plantarflexion of the ankle

Question 20

what is the third class lever?

Answer 20

when the effort is between the fulcrum and the resistance
e.g: elbow flexion
(this lever can be found in all joints of the body)

Question 21

what is the effort arm?

Answer 21

the distance between the fulcrum and effort

Question 22

what is the load arm?

Answer 22

distance between the fulcrum and the load

Question 23

what is a mechanical advantage?

Answer 23

when the effort arm is longer than the load arm

• lever system can move large loads over a short distance
• requires little force
• small range of movement
• difficult to generate speed and distance

Question 24

what is a mechanical disadvantage?

Answer 24

when the load arm is longer than the effort arm

• can’t move as heavy loads
• but can do it faster
• large range of movement