Biomechanics Flashcards
What is newton’s first law?
The law of inertia
Give a definition of the law of inertia
A body continues in a state of rest or constant velocity unless acted upon by external or unbalanced forces.
Apply N1 to an athlete in the blocks
The athlete will remain stationary in the blocks
What is inertia?
The resistance of a body to change its state of movement, whether at rest or while moving
What factors effect inertia?
-mass
What is Newton’s second law?
The law of acceleration
Describe the law of acceleration
A body’s rate of change of momentum is proportional to the size of the force applied, and acts in the same direction as the force applied.
Apply N2 to a sprinter coming out the blocks
The greater the force applied to the sprinter, the greater the rate of change of momentum and therefore acceleration out of the blocks.
What is Newton’s third law?
The law of reaction
Give a definition for N3
For every action force applied to a body there is an equal and opposite reaction force.
Give an example of how N3 can be applied to a high jumper
The more action force the high jumper applies in their takeoff jump the more reaction force the floor will apply back and the higher the jumper will leave the ground.
Apply N3 to a batter in Cricket
The more force the batter applies to the ball the more force the ball will apply back and therefore travel further when hit.
What is linear velocity and what is it measured in?
The rate of displacement, measured in m/s
How do you calculate velocity?
Velocity = displacement/time
What is acceleration and what are its units?
The rate of change in velocity, measured in m/s/s
How do you calculate acceleration?
Acceleration = (final velocity-initial velocity)/time
or
Acceleration = force/mass
What is force and what is it measured in?
Force is a push or pull that alters the state of motion of a body and is measured in Newtons
How do you calculate force?
Force= mass x acceleration
Define speed
The rate of change in distance over a given time
Define linear velocity
The rate of change in distance over displacement
What 5 things can forces do to a body?
- accelerate a body
- decelerate the body
- change shape of a body
- change direction
- create motion
What factors affect air resistance?
- frontal cross-sectional area, the smaller the less ar
- shape, how air flows over the whole body
- velocity, greater v = more ar
- smoothness of body
What is air resistance?
A form of fluid friction that opposes the motion of a body traveling through air
What is friction?
the force that opposes the motion of two surfaces in contact
What factors affect friction?
-roughness of ground, increase roughness=increase friction
-roughness of contact surface, increase roughness= increase friction
-temperature, increase temperature= increase friction
-size of normal reaction force, which is equal and opposite to the weight of the athlete
high mass athletes generate more reaction force therefore more friction
What is linear motion?
movement in a straight or curved line where all parts move over the same distance, in the same direction at the same time
Give examples of almost perfect linear motion
Water skiing
skeleton
bobsleigh
ski jump on the way down
what is angular velocity?
Angular displacement/ time
What is angular velocity measured in?
radian/second
What is moment of inertia?
resistance of a rotating body to change its state of angular motion or rotation
How do you calculate moment of inertia and what is it measured in?
mass x distribution of mass from the axis of rotation
kgm2
What is angular momentum?
The amount of momentum possessed by a rotating body
What is angular momentum measured in and how do you calculate it?
kgm2rad/s
angular velocity x moment of inertia
What factors affect the moment of inertia of a rotating body?
-mass of the body
-Distribution of mass from the axis
of rotation
Describe the relationship between angular velocity and moment of inertia
If a body has a high moment of inertia it will have a lower angular velocity and if a body has a low moment of inertia it will have a higher angular velocity
What is the angular analogue of Newton’s first law?
A rotating body will continue to turn about its axis of rotation with constant angular momentum unless acted upon by an eccentric force or external torque
Apply the angular analogue of newton’s first law to a gymnast performing a somersault
The gymnast will have a constant angular momentum until she hits the floor however she changes her body position by redistributing her mass closer to the axis of rotation which decreases her moment of inertia therefore her angular velocity can increase
Angular momentum cannot change throughout the movement, what is this termed as?
A conserved quantity
Explain the conservation of angular momentum when a gymnast is in the take-off phase of a somersault
-Gymnast generates angular
momentum through an eccentric reaction force from the floor through their body
-They begin to rotate about the transverse axis
- The distribution of their mass is away from the transverse axis so moment of inertia is high and angular velocity is low enabling them to control the movement
Explain the conservation of angular momentum when a gymnast is in the flight phase of a somersault
- The gymnast distributes their mass close to the transverse axis as they tuck in their arms and legs
- The moment of inertia decreases and the angular velocity increases so they can rotate more quickly
- The angular momentum generated at take-off is conserved as there is no eccentric force
Explain the conservation of angular momentum when a gymnast is in the landing phase of a somersault
- The gymnast distribute mass away from the transverse axis by untucking their arms and legs
- This increases their moment of inertia and decreases the angular velocity so slows their speed of rotation down allowing them to have more control of their landing
- As they land the floor applies an eccentric force to remove the conserved angular momentum, allowing the gymnast to stand at the end of the somersault
What factors affect stability?
- height of centre of mass
- size of base
- position of line of gravity
