Lecture 2: Language of Biomechanics Flashcards
What is the imperial system of measurement based on?
human-sized dimensions and referencing non-standard objects
- non-decimal system
- non-standard names
- units can vary by convention (ie. nautical mile and statute/land mile are not the same number of feet)
What is the system internationale (SI) system of measurement based on?
base units are derived from invariant constants of nature – ie. speed of light, triple-point of water)
- decimal system
- values consistent between countries
- standard prefix system of naming
What are fundamental quantities?
physical quantities from which all other quantities are derived
What are the 3 fundamental quantities?
mass, length, and time – all mechanical quantities can be expressed in terms of only these quantities
What unit system is used to describe the fundamental quantities?
MKS system of units (SI units) – meter, kilogram, second
What is length (l) defined by?
defined by speed of light = length of path travelled by light in a vacuum in 1/299,792,458 of a second
What is mass (m) defined by?
cubic decimeter (10 cm x 10 cm x 10 cm) of pure water (1 kg = 1000 cm3 or 1 L of water)
Analyzing the relationships between different physical quantities by identifying their fundamental quantities (M, L, T) allow you to do what?
allows you to determine if your equation is dimensionally consistent, BUT does NOT tell you if the equation is logically correct
ie. dimensionally sound, but physically flawed
How do you identify a meaningful physical equation?
either side of the equal sign of an equation will have the same dimensions
What is a scalar?
physical quantity that has magnitude
ie. mass, length, area, volume, speed, density, pressure, energy, work
What is a vector?
physical quantity that has magnitude and direction
ie. acceleration, velocity, direction, momentum, force, displacement, lift, drag, thrust, weight
What is Newton’s 1st Law?
a body stays at rest or in uniform motion in a straight line unless a force is applied to it
What is Newton’s 2nd Law?
acceleration is proportional to the applied force and is in the same direction as the force
What is Newton’s 3rd Law?
when one body exerts a force on another, the second always exerts a force on the first – the two forces are equal in magnitude, opposite in direction, and act along the same line (action/reaction)
What is force?
any influence that causes an object to undergo a change in its movement, direction, or geometrical construction
can cause an object with mass to change its velocity, accelerate, or deform
What is acceleration?
change in velocity over time
Force without Acceleration
- when BALANCED forces act on an object that is STATIONARY, there is no movement (no acceleration)
- when BALANCED forces act on an object that is IN MOTION, there is constant velocity (no acceleration)
Force Producing Acceleration
- when UNBALANCED forces act on a rigid object that is STATIONARY, it will move (acceleration) in the direction of the force
- when UNBALANCED forces act on an object that is IN MOTION, there is either acceleration (positive or negative if the forces are in line) OR a change in a direction (if the force is perpendicular to the direction of motion)
What is work?
displacement that occurs when a force is applied to a body in the direction of the force
work = force x displacement x cos θ
What is cos θ in the equation for work?
angle between the two vectors force and displacement – this accounts for how much of the force is in the direction of the displacement
When is a force not doing any work?
when the force and displacement are 90º to one another, the force cannot be causing the displacement
What is power?
rate at which work is done (energy is generated or consumed)
What is 1 atm at sea level in kPa?
101.3 kPa
What is the pressure difference between the lowest terrestrial point in the atmosphere (dead sea = 106 kPa) to the highest (Mt Everest = 30 kPa)?
3-fold
What does atmospheric pressure affect?
- respiration
- flight
How much does hydrostatic pressure increase with depth?
pressure increases by 1 atm with every 10 m of depth
How does hydrostatic pressure vary?
pressure varies from 101.3 kPa at the surface to 110,000 kPa (> 1000-fold)
How is pressure and volume of a gas in a container related?
pressure and volume are inversely proportion
- P1V1 = P2V2
- if pressure doubles, volume is halved
Pressure in fluids is omnidirectional. What does this mean?
at any given point within a fluid, the molecules are pressing equalling in all directions
for an object surrounded by a fluid (liquid or gas), pressure is exerted at 90º (normal) to the surface of the object
