Basic biomechanics (wk3) Flashcards
Describe the 2 main forms of biomechanical analysis (and types of motion and movements)
-Biomechanics -> Study of bones, muscles and forces on the body
-Kinematics = Description of movements
-Kinetics = Description and explanation of movements
-Types of motion -> rectilinear, curvilinear and angular
-Body segments are considered to be rigid bodies for the purposes of kinematic analysis -> includes the foot, shank, thigh, pelvis, thorax, hand, forearm, upper-arm and head
-Movements occur at joints between adjacent segments -> include the ankle, knee, hip, wrist, elbow and shoulder
Explain why a spatial reference system is important for kinematic analysis:
-Position -> location of a body in space at some instant in time
-Most labs use a cartesian coordinate system -> origin (0,0)
-Position can also be described by 3 values -> Z, X, Y
-Kinematic data collection -> inertial system, electromagnetic system and optical system
-Joint angles (relative angle) -> is the angle between the 2 segments on either side of the joint
-Segment angle (absolute angle) -> is the angle of the segment with respect to the right-hand horizontal (these changes according to the orientation of the body)
Distinguish between vectors and scalar forms of kinematic analysis:
-Scalars can be describes by magnitude e.g. mass, distance, speed and volume
-Vectors have both magnitude and direction e.g. velocity, force and acceleration
-Vectors are represented by arrows
Describe distance, displacement, speed and velocity:
-Distance -> Scalar quantity. Length of the path followed by an object in motion -> Direction of motion is not considered
-Displacement -> Vector quantity. The straight-line distance from initial position to the final position
-The units of distance and displacement is metres
-Speed measures the rate of motion. No direction so scalar quantity. Speed = distance/time
-Velocity also measures the rate of motion. But in a specific direction so vector quantity. Velocity = displacement /time
Explain the relationships between position, displacement, velocity and acceleration:
-Relationship between position and velocity. The ‘slope’ tells you the velocity direction. Positive slopes mean positive velocities (and vice versa). You can have a positive velocity but either be slowing down or speeding up.
-Acceleration -> An object is said to accelerate if there is any change in its velocity. This includes when an object speeds up, slows down, starts, stops, or changes direction. Acceleration = velocity/time. The units are metres per second per seconds (m/s2). Velocity is a vector so we can speak about a positive or negative acceleration.
-Relationship between velocity and acceleration. The ‘velocity slope’ tells you the acceleration direction. Positive slopes mean positive accelerations (and vice versa). You can have a positive velocity but either be slowing down or speeding up.
Describe ‘force’:
-Forces are pushes or pulls which enable us to start or stop moving, change direction or maintain balance
-Forces occur in pairs
-Characteristics; vector (magnitude and direction), point of application and line of application
-It’s measured in Newtons (N) -> 1N=1kg x 1.0ms-2
-Force = mass x acceleration
Describe the characteristic of forces (forces within the human body):
-Tensile forces -> pulling forces acting on the ends of an internal structure (muscles onto tendons onto bones) – act internally
-Compressive forces -> pushing force acting on the ends of an internal structure (bones onto cartilage onto bones) – act internally
-Colinear forces -> same line of action; same or opposite direction
-Resultant force -> vector addition of 2 or more forces
-Net force -> vector addiction of all the external forces acting on an object
-Concurrent forces -> Act through the same point of application but not on the same line. Resultant of 2 or more concurrent forces depends on both magnitude of each force and angle of application
Differentiate between contact and non-contact forces:
-External forces act on an object as a result of its interactions with the surrounding environment
-Contact forces -> ground reaction force, friction, air resistance
-Non-contact forces -> gravity, electromagnetic
-External forces -> air resistance, body weight, friction and ground reaction
Explain what a free-body diagram represents:
-A free body diagram is an illustration that shows the forces acting on an object in a given situation
-Horizontal -> friction, air resistance
-Vertical -> weight and ground reaction/force
Define body weight and explain how this differs from body mass:
-The force of gravity acting on an object is termed its ‘weight’ (measured in Newtons). W=mg.
-All objects attract each other with a gravitational force
-Mass refers to how much ‘stuff’ is present in the object at the time. Body mass = 100kg
-The closer the objects are, the greater forces each will experience. The larger object will exert more force onto a smaller object and the smaller object will exert its force onto the larger object. Acceleration due to gravity is 9.81 m/s/s. (Newton’s Law of gravity)
Describe what centre of gravity means:
-The centre of gravity is the point through which the resultant force of gravity acts on a body ad the entire weight of the body is balanced
-In humans the centre of gravity (COG) is near the waist (roughly) 53-57% of standing height. Can depend on body composition and whether you’re a female or male.
-The COG position is dependent on the distribution of weight
Explain how a variety of body movements will change a persons centre of gravity:
-When jumping, the end height of the COG is entirely determined from the ground reaction forces versus body weight
-The Fosbury Flop technique manipulates the COG under the body which allows greater heights to be achieved. The athlete passes over the bar while the COG passes through or underneath.
State Newton;s three laws of motion:
-Forces associated with linear motions can be analysed using Newton’s laws of motion;
1. Law of Inertia -> ‘Every body continues in its state of rest, or uniform motion in a straight line, unless its is acted upon by an external force’. Inertia is the resistance of a body to change its motion (i.e. an object’s resistance to a change in velocity)
2. Law of Acceleration -> External forces cause acceleration. If an object accelerates then a net external force must be acting on the object. Acceleration = Total force / mass.
3. Law of reaction -> ‘For every action, there is always an equal and opposite reaction’. Example = If object A exerts a force on another object B, then object B exerts the same force on object A but in the opposite direction.
Discuss the relationship between net external force, mass and acceleration
-Linear momentum is the object’s mass multiplied by its linear velocity (p (kg m/s) =m x v)
-Effect of unbalanced forces -> An object will accelerate in the direction of the net force (if it does not equal to zero)
-If an object accelerates then a net external force must be acting on the object. Acceleration = Total force / mass.
-Example if ground reaction force v body weight. If a person runs, they exert an action force on the ground, whilst the ground exerts a ‘reaction force’ on the person. If the ground reaction force is greater than the persons body weight, then they will accelerate upwards. The NET external vertical force will accelerate the runner up or down.
Explain how Newton’s laws of motion help us to determine changes in a person’s motion:
- Law of Inertia -> The presence of a net external force will cause an object to accelerate
- Law of Acceleration -> Specific relationship between the object’s mass, the net external force experienced and the acceleration it produces
- Law of reaction -> For every force there is an equal and opposite reaction force (mainly on the external forces from the objects perspective)
