Biomechanics - forces

Question 1

What is a force?

Answer 1

the pushing or pulling action that one object exerts on another

Question 2

What is an internal force?

Answer 2

the actions of your muscles

Question 3

What is an external force?

Answer 3

another force acting on you E.G gravity

Question 4

What are the 3 laws of motion?

Answer 4

1) the law of inertia
2) the law of acceleration
3) the law of reaction

Question 5

What does a force platform measure?

Answer 5

ground reaction forces (GRF)

Question 6

List the pros of embedded force platforms

Answer 6

• accurate and reliable 3D force measurements
• high sampling frequency and resolution

Question 7

List the cons of embedded force platforms

Answer 7

• often restricted to indoor use and single step
• possibly unnatural gait (force plate targeting)
• expensive

Question 8

Which type of force platforms are typically used in labs?

Answer 8

embedded force platforms

Question 9

What does portable force platforms measure?

Answer 9

vertical force

Question 10

What is the equation for force?

Answer 10

force = mass x acceleration

Question 11

What is a triaxial accelerometer?

Answer 11

• measures instantaneous acceleration
• at rest will measure 1 g (1 gravity) due to gravity
• orientation is important

Question 12

What are triaxial accelerometers often used to measure?

Answer 12

• physical activity
• quantity/intensity
• ‘load’ monitoring

Question 13

List the pros of accelerometers

Answer 13

• cheaper than lab equipment
• easy to use
• often embedded within other devices
• can monitor closer to the site of interest

Question 14

List the cons of accelerometers

Answer 14

• valid for intended purpose
• affect the movement being monitored
• battery life
• comfort

Question 15

What is the equation for weight?

Answer 15

weight = mass x acceleration due to gravity

Question 16

What is the equation for impulse (Ns)?

Answer 16

impulse = force (N) x time (s)

Question 17

On a graph what is impulse equal to?

Answer 17

the area

Question 18

Since impulse = Ft, what does that also mean impulse is equal to?

Answer 18

change in momentum

Question 19

What is the equation for rate of force development?

Answer 19

rate of force development = change in force/ time taken

Question 20

What is vertical average loading rate (VALR)?

Answer 20

average gradient between 20-80% of impact peak

Question 21

What is the vertical instantaneous loading rate (VILR)?

Answer 21

maximum gradient before impact peak

Question 22

What is the equation for moment?

Answer 22

moment (or torque) = force x perpendicular distance

Question 23

What is moment?

Answer 23

rotational equivalent of force

Question 24

What is friction?

Answer 24

a force that acts in the opposition to the movement of one surface over another

Question 25

What is the equation for friction?

Answer 25

friction = coefficient of friction x normal force

Question 26

What is normal force?

Answer 26

perpendicular to the surfaces in contact

Question 27

List the 3 types of friction

Answer 27

- static - sliding - rolling

Question 28

What is fluid friction?

Answer 28

objects moving through a fluid

Question 29

What are the 2 types of fluid friction?

Answer 29

- aerodynamics (air) - hydrodynamics (water)

Question 30

What are the 4 things needed for drag force that affect air/water resistance?

Answer 30

p = density of the fluid v = relative velocity A = surface area CD = drag coefficient

Question 31

How would you work out the velocities when they are going in opposite directions?

Answer 31

the sum of them both

Question 32

How would you work out the velocities when they are going in the same directions?

Answer 32

the difference of them

Question 33

What are the 2 types of flow?

Answer 33

- laminar - turbulent

Question 34

List the features of laminar flow

Answer 34

- fluid slides smoothly over - layers flow in parallel lines - little disruption to fluid

Question 35

List the features of turbulent flow

Answer 35

- less orderly (less predictable) - greater impact on object, slows object - boundary layer composed of vortices that increase surface friction, more disruption - common at rear of non-streamlined objects

Question 36

What are the difference between laminar and turbulent flow?

Answer 36

- turbulent causes more friction - laminar causes less resistance to movement

Question 37

What does it mean if there is a greater relative velocity?

Answer 37

- more disturbance of fluid around object - have to work harder to overcome fluid forces

Question 38

How can we reduce drag?

Answer 38

- smaller surface area - slower relative velocity - more streamlined shape