Topic 4.3 - Biomechanics Flashcards
Scalars and Vectors
Scalar quantity has only magnitude (size)
Vector quantity has both magnitude and direction
Distance
Distance (d) – How far an object travels
Does NOT depend on direction
Displacement (s)
The difference between an object’s final position and starting position
DOES depend on direction
Speed
A scalar quantity that measures how fast an object is moving
“The rate at which an object covers distance.”
An object with no movement at all has a zero speed.
Velocity
A vector quantity that measures both the speed and direction of an object’s motion.
Speed vs Velocity
Speed = how fast you are travelling
Velocity = speed in a given direction
Equation for Velocity
speed (velocity) = distance travelled/time taken
The Formula Triangle
distance = velocity x time
velocity (speed) = distance / time
time = distance / velocity
Acceleration (a) m/s²
Rate at which an object changes its velocity
change in velocity, direction or both = acceleration
It’s calculated using the equation:
acceleration = change in velocity / change in time
change in velocity = final velocity - initial velocity
change in time = finish time - start time
What is a force?
A push or pull upon an object resulting from the object’s interaction with another object
4.3.7 Define Newton’s three laws of motion.
Law 1: The Law of Inertia
Law 2: The Law of Acceleration
Law 3: The Law of Action/Reaction
Newton’s First Law
Inertia is the natural tendency of an object to resist changes in motion
If an object is motionless, it will want to remain motionless, if an object is moving, it will want to continue moving at same speed, same direction, unless acted upon by an unbalanced force
The more mass….the more inertia
Newton’s Second Law
When forces are unbalanced in a particular direction, there is a NET FORCE
forces are balanced (no net force) = travels at constant velocity
Acceleration is proportional to net force
Mass is inversely proportional to net force
net force = mass x acceleration
F = ma
Newton’s Third Law
Every action has an EQUAL and OPPOSITE reaction
When two objects interact, there is a force on each object
magnitude of force on the first object = magnitude of force on the second object
direction of force on the first object is opposite the direction of force on the second object
Momentum
The quantity of motion of a moving body, measured as a product of its mass and velocity
Momentum (kg.m/s) = Mass (kg) x Velocity (m/s)
p = mv
The relationship between
mass and velocity for momentum
Doubling the mass, doubles the momentum
Quadrupling the velocity, quadruples the momentum
Linear relationship
4.3.3 Define the term centre of mass.
Point at which the mass and weight of an object are balanced in all directions
The lower the centre of mass the more stable the object
Can be outside the body aswell
Base of Support
The location on a body or object where most of the weight/mass is supported.
The larger the area the base covers, the more stable the object will be.
Line of Gravity
An imaginary vertical line through the centre of mass/gravity straight down to the earth
If the line of gravity falls within the object’s base of support the (i.e. its contact with the ground), the object is relatively stable
If the line of gravity falls outside of the base of support, the object is relatively unstable
Stability
Stability is dependant on the COM being directly above the BOS
Factors Affecting Stability
Position of the Centre of Mass
Position of the Line of Gravity
Mass of the Athlete
Size of the Base of Support
Torque
A force that rotates a body about an axis
Angular (Rotational) Momentum
Amount of angular (rotational) movement
The ice skater will continue to spin until another torque acts to change that state.
Conservation of angular momentum
The angular momentum of a system remains constant unless acted on by an external torque
To slow down (rotation), increase moment of inertia (for example opening arms in the skater example)
To increase speed (rotation), decrease moment of inertia (for example bringing arms close to the body)
Angular Momentum Formula
Angular Momentum = Angular Velocity x Moment of Inertia
Angular velocity
the rate of change of angular position of a rotating body
4.3.11. Explain the factors that affect projectile motion at take-off or release.
Angle of Release
Speed of Release
Height of Release
Optimal Release Angle
Depends on release height and landing height
RH > LH = < 45˚
RH = LH = 45˚
RH < LH = > 45˚
Speed of release
The magnitude of the projectile’s velocity vector at the instant of release
When projectile angle and height are held constant, speed of release will determine range
Height of release
If speed of release = angle of release for two shot-put athletes, the taller athlete has an advantage;
Bernoulli’s Principle
Velocity and pressure have an inverse relationship
Fluid velocity increases, pressure decreases
Fluid velocity decreases, pressure increase
Magnus Effect on Top Spin
Top of ball:
Surface of ball is travelling opposite to air flow –> air slow down –> high pressure
Bottom of ball:
Surface of ball is travelling the same direction of air flow –> air speeds up –> low pressure
Consequences:
Pressure difference cause ball to deviate toward area with lower pressure –> dips to the ground
Magnus Effect on Back Spin
Top of ball:
High velocity flow –> low pressure
Bottom of ball:
Low velocity flow –> high pressure
Consequences:
Ball deviate towards area with lower pressure –> stays up longer
Principles of Levers
Levers are…
- Simple machines that help us apply force.
- Rigid structures, hinged at some part with forces applied at two other points.
All levers have three parts…
Fulcrum (Axis) - The pivot point
Load (resistance) - The weight that needs to be moved
Effort - The force that is applied to move the resistance (or load)
Functions of a Lever
increase the load (or force)
increase the velocity
4.3.5 Distinguish between first, second and third class levers.
If F is in the middle: 1st class
If R is in the middle: 2nd Class
If E is in the middle: 3rd Class
First Class Levers
Second Class Lever
Third Class Lever
Impulse
To change momentum we need to apply an impulse
j = force x time
Impulse = the change in momentum
Impulse is the area under the force-time graph
