Introduction to Forces and Newton's Laws (1)

Question 1

state what it is meant by the key term - biomechanics

Answer 1

biomechanics is the study of structure and function of biological systems by the means and methods of mechanics

Question 2

state what it is meant by the key term - force (static)

Answer 2

the push or pull on an object, resulting from the object’s interaction with the environment

Question 3

state what it is meant by the key term - force (dynamic0

Answer 3

the influence that causes a mass to be accelerated

Question 4

what are the units of force ?

Answer 4

Newtons (N)

1 N = 1 kg m/s²

Question 5

what does the specific point of force application determine ?

Answer 5

determines whether the resulting motion is linear, angular, or both

Question 6

what is the line of action of a force ? (2 points)

Answer 6

1) a straight-line length in the direction in which the force is acting
2) a force can be assumed to produce the same acceleration of the object if it acts anywhere along its line of action

Question 7

state what it is meant by the key term - angle of application of a force

Answer 7

the orientation of the line of action to this system is given an angular position and is referred to as the angle of application (θ)

Question 8

what is the difference between ‘coplanar’ and ‘concurrent’ forces

Answer 8

coplanar - a system of forces acting on a single plane

concurrent - a number of forces acting on a single point

Question 9

state 2 facts about ‘concurrent coplanar forces’

Answer 9

1) any set of concurrent coplanar forces may be substituted by a single force, or the resultant, producing the same effect as multiple forces
2) the process of finding tis is called composition of vector forces

Question 10

state what it is meant by the key term - co-linear system

Answer 10

when forces act on a single line, the system is said to be co-linear

Question 11

state what it is meant by the key term - ‘Newton’s 1st Law of Inertia’

Answer 11

a body will remain in a position of rest, or constant velocity, unless acted upon by an external force causing it to change motion

Question 12

state what it is meant by the key term - inertia

Answer 12

inertia is the resistance of a body to change its state of motion

Question 13

state 2 additional facts about inertis

Answer 13

1) inertia is directly proportional to the athletes mass

2) an athletes mass is the same, regardless of where it is measured (e.g. - the moon)

Question 14

state what it is meant by the key term - ‘newton’s 2nd Law of Acceleration’

Answer 14

a body will accelerate in the direction of the force applied, and will accelerate directionally proportionally to the magnitude of the force applied

Question 15

what is the formula for Newton’s 2nd Law of Acceleration?

Answer 15

F = ma

Question 16

what can Newton’s second law be written as ?

Answer 16

△p / △t

Question 17

state what it is meant by the key term - momentum (p)

Answer 17

momentum (p) is the quantity of motion of an object

p = m x V

Question 18

state what it is meant by the key term - Newton’s 3rd Law of Action-Reaction

Answer 18

for every action there is an equal and opposite reaction. all reaction forces are equal in size and opposite in direction to all action forces

Question 19

how does anything move at all (Newton’s 3rd law)

3 points

Answer 19

1) we use the mass of the earth to our advantage
2) the action-reaction are acting on different objects
3) the result is that the two forces cannot cancel each other out because they may have a different effect on the two different objects

Question 20

state what it is meant by the key term - non-contact forces

Answer 20

forces that are exerted by objects that are not in direct contact with one another, and may actually be separated by a considerable distance

Question 21

state what it is meant by the key term - centre of gravity (COG)

Answer 21

the point of origin of the weight vector is the centre of gravity. this is the point at which ass parts of the body are evenly distributed

Question 22

how does centre of gravity (COG) differ from the COM

Answer 22

the COG only refers to the vertical direction because that is the direction in which gravity acts, but the COM does not depend on vertical orientation

Question 23

state what it is meant by the key term - contact forces

Answer 23

contact forces involve the actions, pushes, or pulls, exerted by one object in direct contact with another object

Question 24

state 3 examples of contact forces

Answer 24

GRF, friction, fluid resistance, inertial force, muscle force, elastic force

Question 25

if we are concerned with vertical motion, and the forces determining that motion, what 4 things do we need to consider?

Answer 25

1) we must consider the weight force (Fw) when calculating the vertical force
2) to calculate the resulting acceleration, we must calculate the net vertical force
3) depending on the direction of movement, Fw may be supporting or opposing the intended motion
4) the total and new vertical forces may not be equal

Question 26

state what it is meant by the key term - ground reaction force (GRF)

Answer 26

GRF is the reaction force provided by the surface upon which one is moving

Question 27

GRF can be resolved into 3 components. what are they ?

Answer 27

1) Fz = vertical (up and down)
2) Fy = antero-posterior (forward and backward)
3) Fx = medio-lateral (side to side)

Question 28

which components of GRF are referred to as the ‘sheer components’, why?

Answer 28

medio-lateral and antero-posterior

sheer components as they act parallel to the ground

Question 29

what piece of equipment is usually used to measure GRF?

Answer 29

a force plate/platform

Question 30

how does a force platform work ? (2 points)

Answer 30

1) in senses the deformation produced by the applied force (electrical charge) which is proportional to the force
2) its very accurate, with sampling frequencies that may vary (e.g. - 50 Hz for balance, 2000 Hz for impacts)

Question 31

state 4 facts about the load cells in force plates

Answer 31

1) 4 load cells measure GRF in 3D
2) ant/post =. x
3) med/lat = y
4) vertical = z

Question 32

what must be done when a joint reaction force is conducted ?

Answer 32

the segment is separated at the joints, and the forces acting across the joints must be considered

Question 33

state what it is meant by the key term - ‘joint reaction force’

Answer 33

when a muscle exerts a force across a joint, the muscle on the other side of the joint exert a force of equal magnitude back across the joint

Question 34

state 2 additional facts about the ‘joint reaction force’

Answer 34

1) does not reflect the bone-to-bone force across a joint

2) this is the sum of the actively contracting muscle forces pulling the joint together, and the joint reaction force

Question 35

state what it is meant by the key term - friction

Answer 35

friction is a force that acts parallel to the interface of two surfaces that are in contact during motion, or impeding motion as one surface moves across another

Question 36

what is friction force due to?

Answer 36

the bonding of molecules

Question 37

what is friction proportional to ? (3 points)

Answer 37

1) proportional to the force between the surfaces
2) F = u x N
3) where ‘u’ = the coefficient of friction, and ‘N’ is the normal force perpendicular to the surface

Question 38

what does the coefficient of friction ‘u’ depend on ? (2 points)

Answer 38

1) depends on the nature of the interacting forces
2) the greater the magnitude of the coefficient of friction, the greater the interaction between the molecules of the interacting surfaces

Question 39

sliding and rolling friction are types of what ?

Answer 39

kinetic friction

Question 40

state what it is meant by the key term - rotational friction

Answer 40

rotational friction is the resistance to the rotational or twisting movements

Question 41

what occurs when the coefficients of friction are too small or too large?

Answer 41

too small = slip hazards

too large = trip hazards

Question 42

through the analysis of Newton’s 2nd law of acceleration (F = ma), three general approaches to exploring kinetic and kinematic quantities occur. what are they?

Answer 42

1) the effect of a force at an instance in time
2) the effect of a force applied over a period of time
3) the effect of a force applied over a distance