BIOMECHANICAL PRINCIPLES & LEVERS
Newton’s Laws of linear motion
1. Law of inertia
A force is required to change the state of motion
Inertia: the resistance an object has to a change in its state of motion
Forces are equal/balances (resultant force = 0N)
In football, the ball with remain on the spot at rest unless it is kicked
2. Law of acceleration
Size and direction of force applied to the body (resultant force) determines size and direction
of acceleration
Force = Mass x Acceleration
When the forces are unbalanced, there is a change of speed
3. Law of action/Reaction
To every force there is an equal and opposite force
Centre of mass
The point of concentration of mass / the point of balance. The human body is irregular so the
centre of mass will change – males have higher centre of mass than women
Factors affecting stability
o Height of centre of mass
o Position of line of gravity
o Area of base of support
o Mass of performer
Levers
First Class Lever
e.g. Triceps in extension of the elbow
Mechanical advantage = Large range of movement, resistance can be
moved quickly
Mechanical disadvantage = Cannot apply much force to move an
object
Second Class Lever
e.g. Plantarflexion of the ankle
Mechanical advantage = Can generate large forces
Mechanical disadvantage = slow, with a limited range of
movement
Third Class Lever
e.g. Biceps in flexion of the elbow
Mechanical advantage = Large range of movement, resistance
moved quickly
Mechanical disadvantage = Cannot apply much force to move an
object
, Linear motion
Scalar quantity – measurements described in terms of magnitude – mass, distance, size
Vector quantity – measurements described in terms of magnitude and direction –
weight, acceleration, displacement, velocity, and momentum.
Mass vs weight
Mass = the quantity of matter the body possesses
Weight = the gravitational force exerted on an object
Distance vs displacement
Distance = measured in metres and is the path a body takes as it moves from the starting
to the finishing position
Scalar quantity – only magnitude (distance)
Displacement = measured in metres and is the shortest route in a straight line between
the starting and finishing position
Displacement is a vector quantity, includes direction
Speed vs velocity
Speed = distance / time
Velocity = displacement / time
Measurement Definition Unit Formula
Mass Quality of matter a body possesses kg Mass = w x g
Distance Path a body takes it moves from the m Distance = speed x
start to finish time
Speed Measurement of a body’s movement / m/s Speed = distance /
unit of time (no reference to direction) time
Weight Gravitational force exerted on an N Weight = mass x
object force (acceleration)
Displacement Shortest route in a straight line m Displacement =
between start and finish velocity x time
Velocity Rate of change of displacement m/s Velocity =
Displacement / time
Acceleration Rate of change of velocity m/s2 Change in velocity /
time
Momentum Product of mass and velocity of an kgm/s Momentum = mass x
object velocity
Newton’s Laws of linear motion
1. Law of inertia
A force is required to change the state of motion
Inertia: the resistance an object has to a change in its state of motion
Forces are equal/balances (resultant force = 0N)
In football, the ball with remain on the spot at rest unless it is kicked
2. Law of acceleration
Size and direction of force applied to the body (resultant force) determines size and direction
of acceleration
Force = Mass x Acceleration
When the forces are unbalanced, there is a change of speed
3. Law of action/Reaction
To every force there is an equal and opposite force
Centre of mass
The point of concentration of mass / the point of balance. The human body is irregular so the
centre of mass will change – males have higher centre of mass than women
Factors affecting stability
o Height of centre of mass
o Position of line of gravity
o Area of base of support
o Mass of performer
Levers
First Class Lever
e.g. Triceps in extension of the elbow
Mechanical advantage = Large range of movement, resistance can be
moved quickly
Mechanical disadvantage = Cannot apply much force to move an
object
Second Class Lever
e.g. Plantarflexion of the ankle
Mechanical advantage = Can generate large forces
Mechanical disadvantage = slow, with a limited range of
movement
Third Class Lever
e.g. Biceps in flexion of the elbow
Mechanical advantage = Large range of movement, resistance
moved quickly
Mechanical disadvantage = Cannot apply much force to move an
object
, Linear motion
Scalar quantity – measurements described in terms of magnitude – mass, distance, size
Vector quantity – measurements described in terms of magnitude and direction –
weight, acceleration, displacement, velocity, and momentum.
Mass vs weight
Mass = the quantity of matter the body possesses
Weight = the gravitational force exerted on an object
Distance vs displacement
Distance = measured in metres and is the path a body takes as it moves from the starting
to the finishing position
Scalar quantity – only magnitude (distance)
Displacement = measured in metres and is the shortest route in a straight line between
the starting and finishing position
Displacement is a vector quantity, includes direction
Speed vs velocity
Speed = distance / time
Velocity = displacement / time
Measurement Definition Unit Formula
Mass Quality of matter a body possesses kg Mass = w x g
Distance Path a body takes it moves from the m Distance = speed x
start to finish time
Speed Measurement of a body’s movement / m/s Speed = distance /
unit of time (no reference to direction) time
Weight Gravitational force exerted on an N Weight = mass x
object force (acceleration)
Displacement Shortest route in a straight line m Displacement =
between start and finish velocity x time
Velocity Rate of change of displacement m/s Velocity =
Displacement / time
Acceleration Rate of change of velocity m/s2 Change in velocity /
time
Momentum Product of mass and velocity of an kgm/s Momentum = mass x
object velocity
