Biomechanics

Question 1

Define angular momentum

Answer 1

The amount of angular motion possessed by a body around a rotating axis
Formula :
Angular momentum = MOI x AV
-> when moment of inertia (resistance to change in angular motion) is high angular velocity is low.

Question 2

How can angular momentum be changed?

Answer 2

To increase angular momentum - body can move limbs closer to centre or axis of rotation
To decrease angular momentum - body can move mass further from the body

Question 3

Example of angular momentum - trampolining

Answer 3

Comparison of two types of flips
In a layout the person’s mass is distributed further away from the axis = high moment of inertia and low velocity.
In a tucked summersault the person’s mass is closer to the axis = a low resistance to inertia and an increased velocity. Therefore faster rate of rotation.

Question 4

Conservation of angular momentum

Answer 4

A rotating body will continue to turn about an axis of rotation with constant motion, unless an external force is applied to it. (Newton’s 1st Law)

Question 5

Example of conservation of angular momentum

Answer 5

Diving - a divers angular momentum should remain constant, until the external force (water) stops the divers momentum.
Skateboarding - a skaters angular momentum should remain constant until an external force (the ground) stops the momentum and momentum equals 0.

Question 6

Moment of inertia equation

Answer 6

MOI = mass x radius of rotation squared

-> the greater the inertia of an object the more difficult it is to change the rotation of an object

Question 7

Explain torque

Answer 7

Torque is how much force is produced in an angular sense.
Equation: Torque = force x perpendicular distance of lever arm
Torque measures how hard something is rotated about an axis

Question 8

How can we increase torque?

Answer 8

Generating a larger force, OR increasing perpendicular distance of lever arm (moment arm)
* more torque will be created when more force is applied further from the axis. (extend moment arm)

Question 9

Example of torque

Answer 9

When a diver leans out before they leave the platform they stand on their tip toes and extend their arms above their head, to increase the moment arm and therefore increases torque.

Question 10

Functions of levers

Answer 10

1. Increase the ability to produce force. By making sure the force arm is longer than the resistance arm.
2. Increase speed by making the resistance arm longer than the force arm.

Question 11

Different classes of levers… 1st class…

Answer 11

1st class - axis is between the force and resistance.

• If the force arm is longer than the resistance arm then the system favours force. Eg crow bar
• if the force arm is shorter than the resistance arm the system favours speed (catapult)

Question 12

2nd class levers

Answer 12

• resistance is between axis and force.
• the force is further from the axis then resistance = favours force
  Eg push up.
  Foot - axis
  Force - being applied to the ground
  Resistance - throughout the body

Question 13

3rd class levers

Answer 13

most common- the body is made up of them)
- the force is between the axis and the resistance
- kind of lever favours speed (humans are built for speed)
Eg baseball pitch. Ball= resistance, Shoulder= axis, muscles in arm = force