biomechanics - in depth Flashcards
(38 cards)
1
Q
Force
A
- A force is a push or pull that acts on an object causing it to deform or accelerate.
E.g. Your muscles generate a force when they contract to allow you to lift a ball. - Forces can be balanced and result in a zero-net force, such as when you carry an object.
2
Q
Mass:
A
The amount of matter of someone. E.g., a person’s mass may be 70kg.
3
Q
inertia:
A
- Tendency for objects to remain in their state of motion (at rest or constant speed).
- Objects with greater mass have more inertia. E.g. Without friction, a ball will continue to roll at a steady speed along the ground due to its inertia.
4
Q
Momentum:
A
A measure of the amount of motion of an object/athlete.
momentum = mass x velocity
5
Q
Conservation of Momentum:
A
- the total momentum before a collision is equal to the total momentum after a collision, so athletes/objects will move off in the direction of the object of greater momentum.
- This is why it is advantageous to have greater mass in sports such as rugby/NFL. In a collision, the players will move in the direction of the player with more
momentum (which is determined by their mass and velocity).
6
Q
Impulse:
A
The rate of change of momentum.
impulse = force x time
(= mass x change in velocity)
7
Q
Momentum breaker:
A
- In sports, we can increase the time over which we change an objects
momentum to reduce the force. - This occurs when we are bringing a moving object to a stop (where its momentum goes to zero). To prevent injury and increase likelihood of success, when catching in cricket, a player will ‘give’ with soft hands to increase time and decrease
the force of ball.
8
Q
Momentum maker:
A
- We can also increase impulse by increasing force applied to an object
and/or the time the force is applied. - This occurs when we have a stationary object and are trying to increase its momentum.
- To hit a tennis forehand winner, we can hit with more force and/or follow through to increase the time the force is applied.
9
Q
Linear motion
A
- Movement entirely in a straight line
- E.g., a skier skiing downhill in a squat position- all body parts moving in same
direction at same time
NOTE: Most human motion is a combination of linear and angular motion.
10
Q
newtons laws:
1st law
A
- The law of inertia
- An object will remain in its state of motion (at rest or constant velocity) unless acted upon by an unbalanced net force.
- E.g. A soccer ball will remain stationary unless kicked. Once kicked, it will keep moving in that direction at a constant velocity unless acted upon by an external force
(such as air resistance or friction from the field).
11
Q
newtons laws:
2nd law
A
- Law of acceleration
Force = mass x acceleration
F = ma - Force applied to an object will produce acceleration in the direction of the force,
directly proportional to the size of the force and inversely proportional to its mass (a = f / m) - E.g. To optimise acceleration (in sports) one can reduce mass or increase force. When two athletes with the same mass come out of the starting blocks in a 100-
metre race, the athlete that applies more force will have a greater acceleration.
12
Q
newtons laws:
3rd law
A
- Action/reaction
- For every force, there is an equal and opposite reaction force.
- The force of a tennis racquet on a ball is equal in size but opposite in direction to the force on racquet by ball. The
ball accelerates at a faster rate because of its smaller
mass.
13
Q
Angular motion
A
- Movement around an axis
- E.g. a gymnast swinging around a bar
- Eccentric force: a force that does not go through thecentre of gravity.
E.g. when you kick a soccer ball off- centre, the ball spins and it will curve as it moves through the air. - Torque: force applied outside of the centre of gravity.
Essentially angular force. - Torque = force x moment arm
- Moment arm is the distance the force is applied from the centre of gravity.
14
Q
Angular momentum
A
- The quantity of rotation of a body around an axis.
Angular Momentum= moment of inertia x angular velocity
Moment of inertia = mass x radius^2
15
Q
Angular momentum
- moment of inertia:
- angle of velocity:
- Conservation of angular momentum:
A
- Moment of inertia: a measure of an object’s reluctance to rotate.
- Angular velocity: how quickly an object spins around an axis.
- Conservation of angular momentum: when no external force acts on an object, there is no change in angular momentum. When airborne, angular momentum is constant/conserved.
- E.g. When rotating in the air, the radius can be decreased by tucking. Since angular momentum is conserved, there is a trade-off between moment of inertia and angular velocity. Hence, by tucking, a gymnast can somersault faster and complete
rotations, before extending their legs to reduce angular velocity to prevent over rotation.
16
Q
SUMMATION OF FORCES/MOMENTUM
A
- The correct timing and sequence of body segments to produce maximal force.
- When throwing, athlete starts with larger heavier muscles to generate force/stability.
E.g., In a throw you start off by moving legs/core, followed by the torso, shoulders, arm and
hand. - Since momentum is conserved, when this is transferred to lighter body parts (of less mass),
they move with much greater velocity (momentum = mass x velocity).
17
Q
SUMMATION OF FORCES/MOMENTUM
To maximise force summation:
A
- Use as many body parts as possible
- Use correct sequence – heavier/ slower (Mv) to lighter/faster(mV) body parts
- Use correct timing – move the next body part when previous body part reaches optimal velocity
- Stabilise – once momentum passes from one body part to another the previous body part must stabilize to reduce the loss of momentum.
- This allows a projectile to be launched with optimal velocity
18
Q
Distance:
A
The distance travelled from start to finish e.g., a 400-metre distance sprint.
19
Q
Displacement:
A
- The straight-line distance from starting point to end point.
- Generally includes a direction. E.g. North, south.
- Displacement in a 400-metre running event is 0m.
- Displacement in a 100-metre spring is 100 m South.
20
Q
speed:
A
- Speed = distance / time
21
Q
velocity:
A
- Velocity = displacement / time
- Generally includes a direction. E.g. +ve, North
22
Q
acceleration:
A
- Rate of change of velocity.
- Acceleration = change in velocity / time
- Acceleration = (final velocity – initial velocity) / time
- At constant velocity there is zero acceleration.
23
Q
projectile motion:
A
A projectile is an airborne object which is under the influence of only gravity and air resistance.
* Follows a ‘parabolic’ path due to the constant acceleration from gravity.
* E.g., a ball that has been thrown into the air. Humans can be projectiles too, like a high jumper!
24
Q
factors affecting projectile motion:
A
- Height of release
- Angle of release
- Speed of release (or velocity of release)
25
factors affecting projectile motion:
Maximum distance
E.g. Throwing a javelin.
* Height of release:
increasing the height of release will generally maximise horizontal
distance if technique is not compromised.
* Angle of release:
o If the height of release is the same as the height of landing, the angle of
release should be 45 degrees.
o If the height of release is less than the height of landing, the angle of release
should be greater than 45 degrees
o If the height of release is greater than the height of landing, the angle of
release should be less than 45 degrees.
* Velocity of release:
increase velocity of release to increase the horizontal distance that the projectile travels.
26
factors affecting projectile motion:
Accuracy
E.g. Shooting a goal in netball.
* Height of release:
the height of release should be as high as possible without
compromising technique.
* Angle of release:
don’t give a specific value for the angle of release. Describe it as high or low depending on the specific objectives of the sport. E.g. to avoid defenders in a shoulder pass a netballer may need a high angle of release.
* Velocity of release:
will increase or decrease depending on what the player needs to do. For example, if the ball is not reaching the hoop they may need to increase
velocity of release, but if the ball keeps bouncing off the backboard and missing, they may need to decrease velocity of release.
27
levers
A lever is made up of a rigid bar, an axis, force and resistance.
In the human body, the bones provide a rigid bar, axis is typically a joint, the force is generated by the muscles and resistance is due to a weight/body.
28
Third class levers
- Force is always in the middle
- Resistance arm > Force arm
- Mechanical advantage < 1
- Built for speed
(increasing lever are length means that with the same force applied - ball can move at a greater velocity)
29
Mechanical advantage
- A measure of the force amplification generated by
a lever.
- Dependent upon the ratio between the length of
force arm (distance from axis to force) and
resistance arm (distance from axis to resistance).
MA < 1 : speed advantage
MA = 1 : balance
MA > 1 : force advantage
*from the axis to the force is the force arm
*from the axis to the resistance is the resistance arm
30
Equilibrium
* A state in which all forces are balanced. E.g., a pen sitting on a table is in equilibrium just as an athlete waiting to start a race is in equilibrium.
* Static equilibrium occurs when an object is stationary all forces total to 0.
* Dynamic equilibrium occurs when an object is moving at a constant velocity and there is no change to its state of motion.
31
Stability
* The resistance to disruption of equilibrium.
* In some cases, such as at the start of a race, one wants to be able to start quickly by being able to disrupt equilibrium through very little movement. This is why the
crouch start is used; it allows an athlete to move their line of gravity close to the edge of their base of support and be less stable.
32
Balance
* The ability to maintain and control equilibrium while stationary (static) or while moving (dynamic).
33
Factors affecting stability
- centre of gravity
- base of support
- line of gravity
- friction
- mass
34
Factors affecting stability
- centre of gravity
* The average position of one’s mass that can be assumed to be the point upon which gravity acts.
* Having a lower centre of gravity makes someone more stable.
35
Factors affecting stability
- Base of support
* When one’s line of gravity falls outside of the base of support, equilibrium is
disrupted.
* Thus, a larger base of support increases stability.
36
Factors affecting stability
- Line of gravity
* A line drawn straight down from the centre of gravity.
* This must be maintained within base of support to maintain equilibrium.
37
Factors affecting stability
- friction
* Greater friction can be generated by wearing spikes/boots which enable greater stability and balance.
38
Factors affecting stability
- mass
* Athletes of larger mass have greater inertia, and according to Newton’s Second Law, require greater force to accelerate (a = f/m).
* E.g., sumo wrestlers have a large mass to maintain equilibrium and not fall over.
