Lecture 2: Language of Biomechanics

Question 1

What is the imperial system of measurement based on?

Answer 1

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)

Question 2

What is the system internationale (SI) system of measurement based on?

Answer 2

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

Question 3

What are fundamental quantities?

Answer 3

physical quantities from which all other quantities are derived

Question 4

What are the 3 fundamental quantities?

Answer 4

mass, length, and time – all mechanical quantities can be expressed in terms of only these quantities

Question 5

What unit system is used to describe the fundamental quantities?

Answer 5

MKS system of units (SI units) – meter, kilogram, second

Question 6

What is length (l) defined by?

Answer 6

defined by speed of light = length of path travelled by light in a vacuum in 1/299,792,458 of a second

Question 7

What is mass (m) defined by?

Answer 7

cubic decimeter (10 cm x 10 cm x 10 cm) of pure water (1 kg = 1000 cm3 or 1 L of water)

Question 8

Analyzing the relationships between different physical quantities by identifying their fundamental quantities (M, L, T) allow you to do what?

Answer 8

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

Question 9

How do you identify a meaningful physical equation?

Answer 9

either side of the equal sign of an equation will have the same dimensions

Question 10

What is a scalar?

Answer 10

physical quantity that has magnitude

ie. mass, length, area, volume, speed, density, pressure, energy, work

Question 11

What is a vector?

Answer 11

physical quantity that has magnitude and direction

ie. acceleration, velocity, direction, momentum, force, displacement, lift, drag, thrust, weight

Question 12

What is Newton’s 1st Law?

Answer 12

a body stays at rest or in uniform motion in a straight line unless a force is applied to it

Question 13

What is Newton’s 2nd Law?

Answer 13

acceleration is proportional to the applied force and is in the same direction as the force

Question 14

What is Newton’s 3rd Law?

Answer 14

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)

Question 15

What is force?

Answer 15

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

Question 16

What is acceleration?

Answer 16

change in velocity over time

Question 17

Force without Acceleration

Answer 17

• 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)

Question 18

Force Producing Acceleration

Answer 18

• 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)

Question 19

What is work?

Answer 19

displacement that occurs when a force is applied to a body in the direction of the force

work = force x displacement x cos θ

Question 20

What is cos θ in the equation for work?

Answer 20

angle between the two vectors force and displacement – this accounts for how much of the force is in the direction of the displacement

Question 21

When is a force not doing any work?

Answer 21

when the force and displacement are 90º to one another, the force cannot be causing the displacement

Question 22

What is power?

Answer 22

rate at which work is done (energy is generated or consumed)

Question 23

What is 1 atm at sea level in kPa?

Answer 23

101.3 kPa

Question 24

What is the pressure difference between the lowest terrestrial point in the atmosphere (dead sea = 106 kPa) to the highest (Mt Everest = 30 kPa)?

Answer 24

3-fold

Question 25

What does atmospheric pressure affect?

Answer 25

• respiration
• flight

Question 26

How much does hydrostatic pressure increase with depth?

Answer 26

pressure increases by 1 atm with every 10 m of depth

Question 27

How does hydrostatic pressure vary?

Answer 27

pressure varies from 101.3 kPa at the surface to 110,000 kPa (> 1000-fold)

Question 28

How is pressure and volume of a gas in a container related?

Answer 28

pressure and volume are inversely proportion

• P1V1 = P2V2
• if pressure doubles, volume is halved

Question 29

Pressure in fluids is omnidirectional. What does this mean?

Answer 29

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