Chapter 2 - Biomechanics Flashcards
What are kinetics?
The study of forces that cause motion
What are Kinematics?
Is the description of the motion
Linear motion
Is motion that occurs either in a straight line or curved path
Angular motion
Takes place when a body moves along a circular path
Mass
Is the quantity of matter found within a particular body
Inertia
Is the resistance of a body to a change in its state of motion
Velocity
Is the rate of the speed an object moves its position
Force
Is the product of mass and acceleration
Force summation
- Is the correct timing and sequencing of body segments and muscles through a range of motion
- Ex. Throwing a javelin requires maximum force
- Ex. Putting in golf requires sub-maximal force
Momentum
Is the product of mass and velocity
- Ex. A body with greater mass moving faster will have greater momentum than a lighter object moving slower
Formula: momentum (p) = mass (m) × velocity (v)
Conservation of momentum
- When two things collide, the combined momentum of two things stays the same
- Ex. Ten pin bowling, the momentum of the bowling ball and the pins when combined are the same pre and post-collision
Angular momentum
- Is greater if the mass is larger and the further the mass will be distributed
Simultaneous force summation
- Is the use of multiple body parts at the same time to produce force
- Ex. A sprinter sprinting off the blocks
Sequential force summation
- Is the activation of body parts that are used in sequence to produce force
- Ex. A high jumper
Moment of Inertia
Is a measure of an object’s resistance to change in its rate of rotation
Newton’s first law
Law of inertia
- Objects will stay at rest or continue to travel in the same direction at a constant velocity unless acted on by an unbalanced force
- Ex. A ball will not move unless a force (foot) is acted upon it resulting in it travelling a distance
Newton’s second law
Law of acceleration
- The acceleration of an object is dependent on the amount of force acting upon the mass of the object
- Ex. Hitting a ball with a cricket bat, then hitting a bowling ball with a cricket bat. Distances will vary based on the mass of the object being hit
Newton’s third law
Law of action reaction
- For every action, there is an equal and opposite reaction
- Ex. A roller bladder pushing off another roller bladder, when there is force by one side, there will be opposite and equal force by the other side, causing each side to move in opposite directions
Ex. Pushing off the blocks in a 100m sprint, pushing into there blocks the blocks push back
Impulse
I = force x time
- Is the product of force and time
- The greater the impulse, the greater the momentum generated
- Ex. A discuss thrower using a standing throw, compared to someone using a full spin prior to release.
Linear distance
Is the total distance covered by an object
Linear displacement
Is the difference between the initial position and final position of an object
Difference between linear distance and displacement
When a swimmer starts at one end of the pool and swims up and back, the distance travelled is 100m and the displacement is 0m. This is because they start and end at the same spot
Angular distance and displacement
Ex. If we were to run around a track, our angular distance would be 360 degrees, but our displacement would be zero, as we have reached the same starting point again (like drawing a circle)
Angular distance
Is the total of all angular changed that result from an object or body part angle between the starting and finishing position
First class lever
- The resistance and the force are on either side of the axis
Ex. A see-saw
Second class lever
- The resistance is between the force and the axis
Ex. A wheelbarrow
Third class lever
- The force is between the resistance and the axis
- These are the most commonly used levers in the human body
Ex. A bicep curl
Projectile motion
- As soon as an object or body is released into the air, it becomes a projectile and is automatically under the influence of two external forces, gravity and air resistance
- Air resistance = Acts horizontally on a projectile as it moves through the air
- Drag forces are created which force the projectile to slow down and reduce flight time and distance
Factors affecting projectile motion
- Velocity
- Mass
- Gravity
- Shape
- Surface area
- Nature of surface area
AF - Velocity
The higher the velocity, the greater the air resistance
AF - Mass
The lower the mass the greater the air resistance
AF - Shape
The more streamlined the objects will experience less air resistance
- Ex. A torpedo in football is going to go further then a drop punt because its shape is less wind resistant
AF - Gravity
Pulls the object to the ground, acting as a vertical force
AF - Surface area
The greater the surface area exposed to the air, the greater the air resistance
- Ex. Badminton shuttle
AF - Nature of surface area
Smooth surfaces decrease drag and are less affected by air resistance.
- Ex. Cyclist wears lycra as it is less windy effected
Speed of release
- Force applied to the projectile will have a large impact on its motion
- The greater the force = greater speed, further it will travel
Angle of release
- In most sporting situations where maximal distance is desired, there needs to be an optimal release angle (45 degrees)
- Equipment can be used to alter the release angle
Ex. 3-iron golf club has a release angle of 23deg while a sand-wedge has a release angle of 55deg
Height of release
- If the angle and speed of the object are constant, an object released from a higher point will travel further.
- A taller athlete who naturally releases a ball when throwing would therefore have an advantage over a shorter athlete.
- Ex. A tennis serve
Equilibrium
- When all forces are balanced
- An object in equilibrium is either motionless or moving with a constant velocity (no acceleration)
- Stastic equilibrium
- Dynamic equilibrium
Stastic equilibrium
The state in which a body has zero velocity and zero acceleration
Dynamic equilibrium
Is the state in which a body is in motion with a constant velocity
Stability and balance
- Stability is the degree to which a body can resist change in its current state of equilibrium
- Balance is the ability to control the state of equilibrium
Static balance
- A person being able to control their body position while stationary
Ex. Ballet
Dynamic balance
A person being able to control their body position while moving
Ex. Playing netball
Factors affecting stability
- Body Mass
- Friction
- Base of support
- Centre of Gravity (COG)
- Location of COG
AF - Body mass
The greater the mass of an object or body, the greater the force required to move it
(Newtons 2nd Law)
AF - Friction
Increasing friction between the body and the surface it is in contact with increases stability of the body
AF - Base of support
The larger the base of support, the greater the stability of an object
AF - Centre of gravity (COG)
- The COG is the point around which the body’s weight is evenly balanced and distributed, regardless of the position of the body
- Can be moved by simply moving body parts
Ex. Rugby players will lean forward as they move towards an opposition
AF - Location of COG
- The COG of a perfectly symmetrical object that has constant density and mass and uniform weight distribution will be in the exact centre of the object.
Ex. Sumo wrestler has there centre of gravity over the centre of their body, will allow greater balance
Tips for increasing stability and balance
- Lowering an objects centre of gravity
- Ensuring the line of gravity is over the base of support
- Increasing the size of the base of support
- Increasing friction between two or more bodies
- Increasing the mass of an object
- Extending the base of support in the direction from which a force is coming
Tips for reducing stability and balance to promote agility
- Raising an objects COG
- Shifting the line of gravity outside the base of support
- Narrowing the base of support
- Decreasing the friction between two or more bodies
- Decreasing the mass of an object
