Equilibrium

Measurement

Process of quantifying physical quantities

Position

Location of an object in space

Velocity

Rate of change of position

Acceleration

Rate of change of velocity

Newton's Laws

Three fundamental laws of motion

Vector

Quantity with magnitude and direction

Vector Addition

Combining two or more vectors

Vector Decomposition

Breaking a vector into components

Torque

Rotational equivalent of force

Gravity

Force pulling objects toward Earth

Center Gravity

Point where weight acts

Equilibrium

Net force and torque equal zero

Stability

Resistance to toppling

Balance

Keeping center of gravity over base

Critical Angle

Angle where toppling occurs

Static Equilibrium

Object at rest with balanced forces

Dynamic Equilibrium

Object in motion with balanced forces

Pivot Point

Axis of rotation

Toppling

When CG moves outside base of support

Leg Spreading

Increases base of support for stability

Lifting Weight

Shifting center of mass to balance load

Amputee Balance

Artificial limbs restore stability

Lever

Rigid bar rotating about fulcrum

Fulcrum

Fixed point of rotation

Mechanical Advantage

Load divided by applied force

Class 1 Lever

Fulcrum between load and effort

Class 2 Lever

Load between fulcrum and effort

Class 3 Lever

Effort between fulcrum and load

M>1

Force smaller than load

M<1

Force larger than load

Speed Advantage

Inverse of mechanical advantage

Evolutionary Design

Biological levers optimized for speed

Crusher Claw

Example of force optimization in nature

Skeletal Muscle

Muscle that moves bones via tendons

Tendon

Connects muscle to bone

Joint

Connection between bones allowing motion

Lumbar Vertebra

Pivot for trunk bending

Spinalis Muscle

Erector spinae muscle group

Compression Force

Force along axis of bone

Hip Joint

Stabilized by muscle forces

Limping

Lean reduces hip joint force

Achilles Tendon

Connects calf muscle to heel bone

Tip-Toe

Achilles tension supports body weight

Friction

Resistance between two surfaces

Static Friction

Friction preventing motion

Coefficient Friction

Ratio Fs/N

Biotribology

Study of friction in biology

Oral Tribology

Lubrication in mouth by saliva

Hair Tribology

Friction affecting hair properties

Textile Tribology

Friction between skin and fabric

Catfish Fin

Friction locks fin upright

Snake Skin

Example of friction use in animals

Blisters

Caused by skin-textile friction

Force

Push or pull on an object

Work

Force times distance

Muscle Force

Force generated by contraction

Equilibrium Condition

Sum of forces and torques = 0

Range Motion

Extent of joint movement