Unit 2: Biomechanics Flashcards
Fundamentals of Biomechanics (4.3) , COM, Levers, Newton's Laws
Type of motion (3)
- Linear: motion in a straight line (1 direction)
- Angular: motion around an axis (rotational motion
- General: combination of linear and angular
Scalars vs Vectors:
- 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)
Terms in motion and motion graphs:
Displacement
(def + letter label + vector/scalar)
- (s)
- the change in position relative to the starting point
- vector
Example: The vertical and horizontal displacement during a long jump
Terms in motion and motion graphs:
Speed (def+scalar/vector)
- the change in position in a set amount of time
- scalar
Terms in motion and motion graphs:
Velocity
(def + letter label + vector/scalar + example)
- (v)
- the change in position, relative to the starting point in a set amount of time
- vector
- example: linear velocity of a sprinter
Terms in motion and motion graphs:
Acceleration
(def + letter label + vector/scalar)
what is negative acceleration
example
- (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
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
- 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
Terms in motion and motion graphs:
Impulse
(def + letter label + vector/scalar)
?= ? x ?
- ( 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
Terms in motion and motion graphs:
Force
(def + letter label+ unit)
- (F)
- a push or pull on an object
- an influence that can chnage the position (location) of an object
- measured in Newtons (N)
Angular motion
Angular displacement
(def + unit)
- change in position around an axis
- measured in degree or rad
Angular motion
Angular velocity
- velocity calculates from angular displacement
Example: the angular velocity of the shoulder during volleyball serve
Angular motion
Angular acceleration
(def + unit)
- acceleration calculated from angular velocity
- measured in rad s^-2
Motion time graphs definition and types (3)
- 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
- 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 - Force vs time
* y axis = force in one direction
* x-axis = time (seconds)
* area under curve = impulse
Center of mass
- the point around which the mass of a body is evenly distributed
or - the point in which the body is balance in all directions
COM and stability
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
How can COM be manipulated
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
What are Levers
- 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)
Levers
1st class levers
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
2nd class lever
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
3rd class lever
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
Newtons laws
what is Newstons first law?
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
Newtons Laws
What is newtons 2nd law
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
Newtons Laws
What is newtons 3rd law
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)
Law of conservation of momentum:
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
Conservation of angular momentum
Relationship between angular momentum and the moment of inertia:
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
Conservation of angular momentum
explain conservation
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.
Projectile motion
Factors that affect projectile motion at take off or release (3)
- 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
Projectile motion
Bernoulli’s principle
- 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
