Quiz 1: vector quantities, forces, and levers

Kinesiology definition

the study of movement

Biomechanics definition

the principles of mechanics applied to biological systems and human movement

What are the two divisions of biomechanics?

Kinematics and Kinetics

What is Kinematics?

Movement outputs; movements without regard for forces that produce motion or movement

What are Kinematics measures?

position, displacement, velocity, acceleration, distance, & speed

What is Kinetics?

movement inputs; forces that produce, start, stop, or modify motion

What are the anatomical structures that are kinetic structures?

muscle/tendon, ligament, capsule, and bone on bone internal forces

What are kinetic measures?

Forces and torque: friction, gravity, ground reaction, air and other external forces

How do kinematics and kinetics differ?

Kinematics describes how things move (like velocity and acceleration) without considering the forces causing the motion, while kinetics describes why things move by studying the forces, masses, and torques that produce the motion

What is a vector?

a quantity that has both magnitude and direction

What is a scalar quantities?

have magnitude but no direction

What is positon?

Location in space relative to some reference system or axis (r)

What are the units for position?

meters/linear OR degrees/angular

What vector quantities, when described negatively, mean a change in direction, not a change in quantity?

position, displacement, velocity, force, torque

What is displacement?

changes in the position of the body

What are the units of displacement?

meters (∆ r) or degrees (∆ θ)

What is the equation of displacement?

position (r) final - position initial (rf - ri)

What is distance?

The length of a path between two points; scalar quantity

What is velocity?

Rate of change in position with respect to time (v)

What is the velocity equation?

v=𝚫r/𝚫time

What does the slope of a position-time graph represent?

velocity (1st derivative of displacement)

What does the slope of a velocity-time graph represent?

acceleration (2nd derivative of displacement)

What are the units of velocity?

meters/second or degrees/second

What is speed?

the rate at which an object covers distance; scalar quantity (no direction)

What is acceleration?

Change in velocity wrt time (a) (aka rate of change of position wrt time)

What are the units of acceleration?

meters/second^2 or degrees/second^2

What is the equation for acceleration?

a = Δv / Δt

What does it mean when acceleration is described as a negative number?

decl. in a ___ direction; if veleocity is + = decleration; if velocity is - = acceleration

Can we figure direction from accleration?

No

What does an acceleration of 0 mean?

An object's velocity is constant or you are not moving

What are force vectors?

A push or pull that tends to change the state of rest of an object or the state of motion of the object.

What is the equation for force?

Force = mass x acceleration

What does force vectors link?

kinematics and kinetics

What is the units of force?

newtons (N)

What is a newton?

the amount of force, that when acting on 1 kg of mass, produces an acceleration of 1 m/s2 (~ 1 apple)

What is the newton equation?

1 N = 1 kg x 1m/s2

What are the force categories?

Discrete vs. Distributed, Contact vs. Remote, Internal vs. External

What is a discrete force?

a single, individualized force acting between two distinct bodies

What is a distributed force?

a force that is spread over a surface, line, or volume rather than concentrated at a single point

What is a contact force?

a force that acts between two objects only when they are physically touching

What is a remote (non-contact) force?

a force that originates from a point in space, not physically on the object itself, but is applied to the object

What is an internal force?

force that acts within object or system

What is an external force?

any force that results from the interaction between the object and its environment

What is gravity?

Force of attraction between any 2 particles

What is the gravity constant?

9.81 m/s2

What is the gravity equation?

W= mg (F=ma)

What type of force is gravity?

distributed, external, remote force

what is the center of gravity? (COG)

vertical projection of COM; is the point of balance wrt gravity

What is the center of mass (COM)?

point at the center of the total body mass; balance point

*moves w/ the body

What is joint reaction force (JRF)?

the equal and opposite forces that exist between ADJACENT BONES at a joint caused by the weight and inertial forces of the 2 segments

What does JRF include?

includes bone-on-bone forces, ligament forces, and muscle forces

What type of force is JRF?

Contact

What are bone-on-bone forces?

the actual forces (axial loading and shear) across the articulating surfaces

What are the JRFs?

Joint contact forces, axial forces, and shear forces

What is a joint contact force?

compressive force resulting from bone-on-bone or ligament

What are axial force?

Compression/distraction; perpendicular to the joint surface

What is shear force?

Perpendicular to axial, parallel to joint surface

What is ground reaction force (GRF)?

The force exerted by the ground on a body in contact with it

What is friction?

A force that opposes motion; parallel to contact surface (normal force and friction)

What is the friction equation?

Ff = uN (N = normal force; u = coefficient of friction)

What is the purpose of friction?

increase grip or impede motion

What is friction independent of?

surface contact

What is fluid resistance (air/water)

Drag (drives resistance), lift (air pushing up), buoyancy (water pushing up)

What is inertia?

Resistance to change in state of rest or motion; proportional to mass, and has linear and angular implications

How does increasing mass affect inertia?

increases inertia

What is muscle force?

force applied by muscle to overcome resistance

What kind of force can muscle apply?

only pulling forces

How is muscle force represented?

As a discrete line vector (as long as no bone deformity)

What is muscle force dependent on?

physiologic cross-sectional area (PCSA) and line of action (orgin/nsertion)

What is the muscle force outcome dependent on?

line of action (origin and insertion)

What is torque?

The ability of a force to cause rotation around an axis

*a force pushes; whether or not it rotates is based on the torque on it

What is the torque equation?

T = F*MA

How is MA related to distance?

perpendicular to the distance (⊥d; lever arm) from the line of action to the axis of rotation

What causes MA to change?

When the angle of pull changes, the position of the joint will change

When does torque change in the body?

as the "angle of pull" changes with changes in the position of a joint; determines muscles function

What is resultant torque?

summation due to multiple forces active at a given time

How do we determine the direction of torque and its sign?

MA will move the "shortest" distance to the axis of rotation. Moving CC (+) or Clockwise (-)

What are anatomical pulleys purpose?

Increase the MA action, increasing mechanical advantage and torque

How do we process force vectors?

by using resolution and composition

What is resolution?

a single force vector is resolved into its components

What is composition?

several force vectors are combined to represent a single vector

What is a free body diagram (FDB)?

a "snapshot" that represents interaction between a system and its environment

What do we need to ALWAYS consider in a FBD?

weight forces (Fw), muscle forces (Fm) , joint contact force (Fj)

What else do we consider for FBD that are context dependent?

GRF, Friction (Normal force (Nf) & friction (Ff)), and any other external forces

What can we assume in FBDs?

joints are frictionless, air resistance can be ignored, and use net muscle moment instead of force

What is the conversion of inches to meters?

1 in = 0.0254 m

What is the equation for the conversion from kg to N?

F(N) = ma or mg (kg); 1 N = 1 kg x 1m/s2

What is the conversion of N to lbs of FORCE?

1lbs = 4.44822 N

What is rotary/angular motion?

movement around a fixed axis in a curved path

What is linear/translatory motion?

motion in a straight line with no axis of rotation; each point moves the same distance

What is general motion?

rotation about a point, which is itself moving; combo of linear and angular

How do we determine the horizontal and vertical components of a muscle/vector?

SOH CAH TOA

How do we determine the resultant/component forces of the horizontal and vertical components?

Sum the Fx and Fy of each component

How do we determine the muscle/resultant vector force?

Pythagorean Theorem

How do we determine the angle of the resultant vector?

tanϴ= Ry/Rx (aka O/A)

What is the line of action of the resultant vector?

The direction of the vector found using the magnitude, angle, and summation of its components

What are the spatial reference frames (SRF)?

absolute, relative, orthogonal, non-orthogonal

What is an absolute RF?

RF won't move itself (e.g. __ relative to the room)

What is a relative RF?

RF will move (e.g. elbow relative to the forearm)

What is an orthogonal reference frame?

includes the cartesian coordinates (x,y,z), allowing us to map vectors