Introduction to Forces and Newton's Laws (2)

Question 1

what is the difference between ‘statics’ and ‘dynamics’ ?

Answer 1

statics - if the resulting force has a value of zero

dynamics - if the resulting force has a non-zero value

Question 2

what does statics refer to

Answer 2

systems moving at rest or at constant velocity (in equilibrium)

Question 3

state what it is meant by the key term - ‘translational motion’

Answer 3

in translational motion, when a system is in equilibrium, all the forces that are acting on the system cancel each other out, and the effect is zero

Question 4

‘concurrent forces do not coincide at the same point, so they cause rotation about an axis’

state 2 facts about this statement

Answer 4

1) these rotations all add up to zero

2) however, because this is a static case, no rotation occurs

Question 5

when must dynamics be used rather than statics?

Answer 5

when accelerations are significant (i.e. - a ≄ 0)

Question 6

what is the equation for acceleration ?

Answer 6

F = ma

Fx = m * ax
Fy = m * ay

Question 7

in the dynamic case, linear accelerations and the inertial properties of the body segments resisting these accelerations must be considered using what technique?

Answer 7

inverse dynamics

often referred to as ‘Newton-Euler-Inverse Approach’

Question 8

explain what the ‘inverse dynamics’ approach is (2 points)

Answer 8

1) calculates forces based off of accelerations of the object
2) analysis starts with most distal limb then moves more proximally

Question 9

state 3 assumptions that are made when using the ‘inverse dynamics’ approach

Answer 9

1) the body is considered to be a rigid link between segments of the system
2) each link, or segment, has a fixed mass and a fixed COM at a fixed point
3) the moment of inertia about any axis of each segment remains constant

Question 10

what is the impulse-momentum relationship ?

Answer 10

F x △t = (m x Vf) - (m x Vi)

Question 11

to change the momentum of an object, what must be done?

Answer 11

a force of large magnitude man be applied over a short period of time, or a force of a smaller magnitude can be applied over a longer period of time

Question 12

state what it is meant by the key term - ‘mechanical work’

Answer 12

mechanical work is equal to the magnitude of a force applied against an object and the distance the object moves in the direction of the force while the force is applied to the object

Question 13

what is the formula for work?

Answer 13

W = f x cos(θ) x s

^ more work is done if force is applied parallel to the direction of motion than if force was applied at an angle

Question 14

state what it is meant by the key term - ‘power’

Answer 14

power is defined as the rate at which force does work

Question 15

what is power plotted as ?

Answer 15

power is plotted on a graph as a function of time, the area under the curve equals work done

Question 16

what is the formula for power ?

Answer 16

P = △w / △t

P = F x (△s / △v)

P = F x V

Question 17

state what it is meant by the key term - energy

Answer 17

energy is the capacity to do work (J)

Question 18

state what it is meant by the key term - kinetic energy (KE)

Answer 18

KE refers to the energy resulting from motion

Question 19

what is the formula for KE ?

Answer 19

KE = 1/2 MV²

^ because the expression includes the square of velocity, any change in velocity greatly changes the amount of KE of the object

Question 20

state what it is meant by the key term - potential energy (PE)

Answer 20

PE is the capacity to do work because of position of form

Question 21

what is the formula for PE ?

Answer 21

PE = m x g x h

Question 22

what is the formula for strain energy (SE) ?

Answer 22

SE = 1/2 k * △x²

^ where ‘k’ is a proportionality constant and ‘△x’ is the distance over which the object is deformed

Question 23

what is it meant by the key term - ‘conservation of energy’

Answer 23

energy cannot be created or destroyed

Question 24

state what it is meant by the key term - closed system

Answer 24

a closed system is one that is physically isolated from its surroundings

Question 25

how can an isolated system be mathematically phrased?

Answer 25

TE = KE + PE

Question 26

the work energy theorem states that the work done is equal to the change in energy

Answer 26

W = △E

Question 27

what is the calculation called for the total work done resulting from the motion of all of the body segments called ?

Answer 27

inertial work

Question 28

for a single segment, the inertial work done by the segment formula is what?

Answer 28

Ws = △(1/2 mV²) + △(m x g x h)

Ws = KE + PE

Question 29

what does energy transfer within a segment refer to ?

Answer 29

energy transfer within a segment refers to changes from one form of energy to another, as in the change from potential to kinetic energy

Question 30

what does energy transfer between segments refer to ?

Answer 30

energy transfer between segments refers to the exchange of total energy of one segment to another

Question 31

state what it is meant by the key term - ‘external work’

Answer 31

external work may be defined as the work done by a body on an object