Biomechanics
Science that studies living things from a mechanical perspective
What is a force
A push or pull
Mass x Acceleration
How do forces affect objects
Change its shape (stretch, squash, twist)
Move the object (speed up, slow down, change direction)
Types of forces
Gravity
Weight
Friction
Drag
Gravity
A constant force that acts through the centre of mass of an object towards the earth
9.8m/s2
Friction
Occurs when two surfaces come into contact with each other, opposing the motion of an object
To start an object moving, you must overcome its friction by applying a greater force
Influenced by surface imperfections and surface area
Drag Force: Air and Water Resistance
Caused by the collision of air and water particles on the object, opposing its motion
Affected by air density, speed, cross sectional area of object
Increase speed means increase drag
Decrease surface area and use tight clothing
Weight and Mass
Mass is the amount of matter an object is made up of (kg)
Weight is the force exerted upon a body by gravity (N)
Weight = Mass x Gravity
Inertia
Tendency of an object to resist a change in its state of motion, whether at rest or constant velocity
Greater mass=greater inertia=greater force to move object
Momentum
Measure of the amount of motion an object has and its resistance to changing that motion
Momentum = Mass x Velocity
Conservation of momentum
Momentum is conserved in an isolated system where there are no external factors acting
“Total momentum of systems before the collision is equal to the total momentum after the collision’
Summation of Momentum
- Sequential and coordinated movements of each body segment to produce maximum velocity
- Max Vel result from momentum generated from body parts closer to centre of gravity to those further away
- larger body parts moving quickly force smaller body parts to move even faster
How to summate momentum
- use as many body parts as possible
- use stronger, larger muscles before quicker and smaller muscles
- coordinating the sequencing of body parts so momentum can be transferred from one muscle group to the next
- create a stable base of support for Movement to occur around
Impulse
change in momentum of an object, mass in motion
Impulse = Force x Time
Manipulating impulse can reduce injury (hands while catching)
Larger force over shorter time or smaller force over longer time
Newtons First Law of Motion
Law of Inertia
A body will remain at rest or in uniform motion in a straight line unless acted upon by a external force
Newtons Second Law
Law of Acceleration
A force applied to an object will produce a change in motion in the direction of the force applied that is directly proportional to the size of force
Newtons Third Law
Law of Action Reaction
For every action there is an equal and opposite reaction
Torque
The turning effect caused by an eccentric force (one that doesn’t act through the objects centre of gravity)
Force x lever arm
Newtons First Law of Angular Motion
The angular momentum of a body remains constant unless acted upon by an external torque
Newtons Second Law of Angular Motion
A torque applied to an object will produce a change in angular motion in the direction of the applied torque that is directly proportional to the size of the torque
Newtons Third Law of Angular Motion
For every torque there is an equal and opposite torque
Angular momentum
Quantity of angular motion of an object
Moment of inertia
The resistance of an object to changes in its state of angular motion
Mass x Radius2
Product of distribution of mass of object and the axis about which it rotates
Conservation of Angular Momentum
Angular momentum is conserved when body is in flight
As angular momentum is constant, and mass is constant, then there is a trade off between moment of inertia and velocity
General motion
Combination of linear and angular motion
Linear motion
Movement of the body where all parts move in the same direction at the same time along a line
Curved line= curvilinear
Straight line= rectilinear
Angular motion
Movement of a body part around an axis of rotation
Projectile motion
The movement of an object through the air
Distance
Measures the path travelled from start to finish regardless of direction
Displacement
Change of position from initial position to final position
Direction of motion is important
Speed
Ratio of the distance covered to the time taken
Speed= distance/time (m/s)
Velocity
Ratio of displacement or change in position to the time taken
Velocity = displacement/time (m/s)
Acceleration
Change in velocity in a given period of time
Acceleration = change in velocity/change in time (m/s2)
Can be positive or negative
Angular distance
Sum of all angular changes the body undergoes in degrees,
Angular displacement
Difference between the initial and final angular position of an object in degrees
Angular speed
Angular distance covered divided by the time taken to complete the motion
Angular velocity
Rate of change of the angular displacement of a body over time
Angular acceleration
Rate of change of angular velocity
Projectile
An object or body that is launched into the air and affected by the forces of gravity and air resistance
Path of an object is affected by
Angle of release
Speed of release
Height of release
Horizontal Trajectory
Projection at 0° or perfectly horizontal
Oblique trajectory
Occurs when the angle of projection is between 0° and 90° (parabolic)
Vertical trajectory
Object travels straight up and down
Best angle for covering the greatest horizontal distance
45°
Speed of release
Greater speed of release = greater horizontal range of projectile
Height of release
Difference between the height of projectile release from height at which it lands
Equilibrium
When all forces and torques are balanced
Static equilibrium
Body/object must not be moving or rotating
-sum of all vertical, horizontal forces and torques must be zero
Dynamic equilibrium
When the body/object is moving with a constant velocity, no change in speed or direction
Stability
Resistance to the disruption of equilibrium
Balance
Ability to control equilibrium
Factors affecting stability
Base of support
Centre of gravity
Body mass
Friction between object and surface its in contact with
Base of Support
Generally, larger BOS the greater stability
Moving one foot behind the other increases forward/backwards stability
Moving one foot further away midline increases side to side stab
Point of contact with the supporting surface
Centre of Gravity
Point around which the body’s weight is balanced
Usually found near naval
Lowering COG increases stability
Line of gravity
Direction in which the gravity acts through the centre of gravity
- when LOG acts through centre of BOS, stability increased
- stability decreased when LOG moves to outside edge of BOS
Body mass
Greater mass of object, greater force required to move it, greater stability
Friction
Increasing friction between object and surface it is contact with increases stability
What is a lever
A simple machine consisting of a rigid bar that can be made to rotate around an axis in order to exert a force on another object
Components of a lever
Axis
Resistance
Force
1st class lever
Resistance and force applied in the same direction with axis in middle
(Seesaw, extending head)
2nd class lever
Resistance and force applied in opposite directions
Resistance closer to axis and force further away
(Wheelbarrow and standing on tip toes)
Third class lever
Resistance and force applied in opposite direction
Force closer to axis and resistance further away
(Catapult, flexing elbow)
Mechanical advantage
Ratio of force arm to resistance arm
Force arm/resistance arm
Force arm: distance from axis to force
Resistance arm: distance from axis to resistance
Mechanical advantage greater than one
Greater force
Less force to move resistance
Mechanical advantage less than one
Increased range of motion and angular speed
Lever length
Longer levers have greater inertia and therefore more difficult to swing
Applying spin to a ball
Applying an eccentric force (one that acts outside an objects centre of gravity) causes objects to rotate and move forward. This turning effect is known as torque