Unit 2: Biomechanics

Question 1

Type of motion (3)

Answer 1

• Linear: motion in a straight line (1 direction)
• Angular: motion around an axis (rotational motion
• General: combination of linear and angular

Question 2

Scalars vs Vectors:

Answer 2

• A quantity can either be scalar OR vector
  Scalar : number + unit = 10.3m
  Vector : number + unit+ direction = 10.3m Forward
• When calculating motion, always attempt to include the direction (vector quantity)

Question 3

Terms in motion and motion graphs:

Displacement
(def + letter label + vector/scalar)

Answer 3

• (s)
• the change in position relative to the starting point
• vector
  Example: The vertical and horizontal displacement during a long jump

Question 4

Terms in motion and motion graphs:

Speed (def+scalar/vector)

Answer 4

• the change in position in a set amount of time
• scalar

Question 5

Terms in motion and motion graphs:

Velocity
(def + letter label + vector/scalar + example)

Answer 5

• (v)
• the change in position, relative to the starting point in a set amount of time
• vector
• example: linear velocity of a sprinter

Question 6

Terms in motion and motion graphs:

Acceleration
(def + letter label + vector/scalar)
what is negative acceleration
example

Answer 6

• (a)
• the chnage in velocity in a set amount of time
• vector

a change in acceleration means there is a change in position
* Negative acceleration doesn’t mean moving backwards
* Negative acceleration means velocity is decreasing
* Example: 5.2 m s-2 [Forward] → 1.2 m s-2 [Forward]

Example: Acceleration of a ball after being kicked / Deceleration of a person during a rugby tackle

Question 7

Terms in motion and motion graphs:

Momentum
(def + letter label + vector/scalar)
? = ? x ?
what does smaller and larger momentum mean compared to the change in velocity

Answer 7

• def: amount an object wants to stay in constant motion
• (p)
• P = mv (mass x velocity)
• smaller momentum = easier to change velocity
• larger momentum = harder to change velocity
• A measure of inertia → more momentum means an object is harder to stop, it wants to continue moving

example: momentum of a bowling ball hitting bowling pins

Question 8

Terms in motion and motion graphs:

Impulse
(def + letter label + vector/scalar)
?= ? x ?

Answer 8

• ( J )
• the amount and how long a force acts on a object
• vector

J=Ft (force x time?)
* the longer a force acts on an object = the larger the impulse
* impulse = change in momentum

examples:
* impulse of shock absorbing in shoes and jumping
* impulse of faster velocity when throwing a ball (winding up vs no windup

Question 9

Terms in motion and motion graphs:

Force
(def + letter label+ unit)

Answer 9

• (F)
• a push or pull on an object
• an influence that can chnage the position (location) of an object
• measured in Newtons (N)

Question 10

Angular motion

Angular displacement
(def + unit)

Answer 10

• change in position around an axis
• measured in degree or rad

Question 11

Angular motion

Angular velocity

Answer 11

• velocity calculates from angular displacement

Example: the angular velocity of the shoulder during volleyball serve

Question 12

Angular motion

Angular acceleration
(def + unit)

Answer 12

• acceleration calculated from angular velocity
• measured in rad s^-2

Question 13

Motion time graphs definition and types (3)

Answer 13

• a way to graphically represent the measure of movement over the itme it takes to perform
  X-axis = time
  Y-axis = velocity or distance or force

types:
1. DIstance vs time
* used to show movement of an object or body part in a single direction
* slope of line = velocity

2. Velocity vs time
   * used to show the velocity of an object or body part in a single direction
   * slope of line = acceleration
   * area under the curve = displacement
3. Force vs time
   * y axis = force in one direction
   * x-axis = time (seconds)
   * area under curve = impulse

Question 14

Center of mass

Answer 14

• the point around which the mass of a body is evenly distributed
  or
• the point in which the body is balance in all directions

Question 15

COM and stability

Answer 15

Stability/balance occurs when the COM stays within the base of support.

Stability can be increased by:
* Lowering COM
* Widening the base of support
* Adding a contact point to enlarge the base of support

Question 16

How can COM be manipulated

Answer 16

By moving our body segments, we can change where the COM is located. The mass of the body will be centered at a different spot as we move.

Examples:
* Raising your arms above your head → COM shifts superiorly
* Holding one arm to the side → COM shifts laterally
* Holding you arms in front of you → COM shifts anteriorly

Question 17

What are Levers

Answer 17

• Simple machines that create a more efficient way of lifting weight
• Using levers you can lift more weight for the amount of force applied. Or move faster

Levers have:
Load (weight)
Fulcrum (joint)
Force/effort (muscle)
Beam (Bone)

Question 18

Levers

1st class levers

Answer 18

fulcrum is between the effort and the load

example: Nodding your head (hyperextension of neck)
Effort: posterior neck muscles
Fulcrum: cervical spine
Load: COM of skull

Question 19

2nd class lever

Answer 19

load is between effort and fulcrum (joint)

example:
Calf raise (plantar flexion)
Effort: gastrocnemius muscle
Fulcrum: joint between metatarsals and phalanges
Load: body weight
Beam: tarsals and metatarsals

Question 20

3rd class lever

Answer 20

effort(muscle) is between load (weight) and fulcrum (joint)

example: Bicep curl (flexion of elbow)
Effort: bicep brachii
Fulcrum: elbow joint
Load: COM of forearm
Beam: ulna/radius

Question 21

Newtons laws

what is Newstons first law?

Answer 21

Law of inertia
an object at rest stays at rest while an object in motion stays in constant motion, unless a force acts on it
Example:
* Balls don’t move without being contacted
* Sprinters have to apply a force to start moving

Question 22

Newtons Laws

What is newtons 2nd law

Answer 22

2nd law :
Acceleration is porportional to the force applied and the mass of the object
* heavy objects = harder to move as a=F/m (force/mass)

examples:
* The more force used in striking a golf ball, the greater its acceleration, hence it will go further
* Using a lighter bat will allow for a greater acceleration of the bat. This will allow for a baseball to be hit with a faster speed without having to swing with more force

Question 23

Newtons Laws

What is newtons 3rd law

Answer 23

for every action force there is an equal and opposite reaction force
* Force comes in pairs, equal in strength but opposite in direction. Allow movements
Example:
* Punching a punching bag, you feel the same force as to what you used to punch the bag. One of the reasons why boxers wrap their hands to train
* Pushing down into the floor allows for you to jump as the floor pushes back on you with the same amount of force in the opposite direction (UP)

Question 24

Law of conservation of momentum:

Answer 24

When two objects collide the total momentum of the two objects before collision has to equal the total momentum of the two objects after the collision
* Momentum before collision = momentum after
* In a collision the object with the least amount of momentum will change directions.

Example:
* A 75 kg rugby player running at the same velocity as a 85kg rugby player will change directions (get knocked over) in a tackle
* Hitting an object further - hit with a heavier item OR swing it faster to causes a greater change of momentum → more momentum change means the object hit will be moving at a faster velocity

Question 25

Conservation of angular momentum

Relationship between angular momentum and the moment of inertia:

Answer 25

Angular momentum = moment of inertia x angular velocity
* Therefore an increase in moment of inertia OR angular velocity will cause an increase in angular momentum

Question 26

Conservation of angular momentum

explain conservation

Answer 26

Angular momentum is conserved unless an external torque force is applied on it
Example: during a spinning motion the total angular momentum stays the same

Angular momentum can be seen in sports such as: figure skating, aerial skiing and diving

• Figure skaters can control how fast they spin by pulling in their arms.
• Angular momentum is conserved (stays the same) during the skater spinning.
• If the skater brings in their arms, they are decreasing the moment of inertia, as the COM moves proximally.
• To conserve the angular momentum, the angular velocity must increase to compensate.

Question 27

Projectile motion

Factors that affect projectile motion at take off or release (3)

Answer 27

• Speed - the greater the initial speed, the farther the object will go
• Height - if the object is launched from higher up, then it will travel further
• Angle of release - release angle matters, too high - not enough forward speed to move a distance. But, too low, not enough upwards speed to keep it in the air

Question 28

Projectile motion

Bernoulli’s principle

Answer 28

• Projectile motion creates areas of high and low pressure around an object
• Objects will move in the direction of the low pressure

example
–> Backspin causes low pressure on top of a ball as air is moving faster, over the top
- This causes increased air time or a “float” effect
- Golf, tennis, goal kicks
* Top spin causes a low pressure under the ball,
–> causing the ball to decrease airtime and dip
–> Tennis, volleyball
* Side spin