Lecture 5

Question 1

What is the first law of motion

Answer 1

-property of an object to resist changes in motion

Question 2

what is momentum?

Answer 2

quantity of motion possessed by a body
M=mv
when tow object collides, both objects would tend to continue moving in the same direction of the object with a larger momentum

Question 3

conservation of momentum

Answer 3

if net external force acting on a system ( one or more) objects equals zero the total system momentum is conserved

M1=M2
(mv)1=(mv)2
M=(m1 +m2)

Question 4

what is the mechanical behavior of when bodies are in contact ( 1st law)

Answer 4

• when 2 objects collied
• this is the exchange of a large force during a small time interval (ball to bat)
• resultant behavior of the object depend on their collective momentum and the nature of the impact

Question 5

what is perfectly elastic impact

Answer 5

in which the velocity of the system is conserved

e=1 (superball bounce)

Question 6

perfectly plastic impact

Answer 6

in which there is a total loss of system velocity

e=0 ( spaghetti hits wall)

Question 7

impacts/ collision

Answer 7

e = (v2-v1)/ (u1-u2)

u= velocities before impact
v=velocities after impact

Question 8

second law of acceleration

Answer 8

F=ma or a= F/m
- remember you can look at this in different directions
such as vertically, horizontally and the Z direction

Question 9

what is the mechanical behavior of when bodies are in contact (2nd law)

Answer 9

when external force do ac there is a change in systems total momentum

to modify this you think about impulse

Question 10

What is Impulse

Answer 10

the product of a force and the time interval over which the force acts

Ft=mv or Ft=mv2- mv1

Question 11

how do you increase momentum using impulse

Answer 11

• throwing a ball ↓v intial but has ↑v final
• you get ↑ in v by having a ↑over in time

–lighter objects the time is greater limitation on impulse than force

–heavier objects the size of the force will limit impulse

Question 12

How do you decrease momentum using impulse

Answer 12

• catching a egg
• by having a give time you are ↑ the time ↓ the F
• remember the right side of the equation will NOT change the v is coming in cant change and you cant change the mass so you have to change time to ↓ the F

Question 13

third law- action / reaction and collisions

Answer 13

when a body exerts a force on another body the second body exerts a reaction force on the first body that is equal in magnitude and opposite in direction

Question 14

ground reaction forces

Answer 14

• grf is the reaction force to the push applied to the ground by the runner
• we resolve the resultant grf into three perpendicular components that each have functional significance during walking and running
• total body weght contributes to total body acceleration in proportion to the acceleration of their own center of mass
• -vertical ( support)
• -anterior- posterior ( propulsion- braking)
• -medial lateral (sway)

Question 15

LOOK at the last slide of 5a

Answer 15

then draw them out!!

Question 16

what is inertia

Answer 16

resistance to change in motion

Question 17

what is angular law of inertia

Answer 17

a rotating body will maintain a state of rest or constant rotational motion unless acted on by an external torque that changes the state

• inertia is represented by the moment of inertia (i)

Question 18

how is linear kinetics represent inertia

Answer 18

this would be mass

Question 19

what is the inertia equations

Answer 19

I=mr2

• the distribution of the mass is more important than the mass itself

Question 20

what influences inertia

Answer 20

• mass of object
• shape
• distance of axis or the rotation form the center of mass
• orientation of axis of rotation (radius)

Question 21

human moments of inertia

Answer 21

• object can only have one linear inertia value ( mass) but multiple moments of inertia due to multiple axes or rotation
• body segments have different axes of rotation and moments of inertia for each plane of motion
• vertical you can tuck you knees in
• horizontial you can move your arms in or out

Question 22

why does a running drive their knees up

Answer 22

by driving your knees up you are ↓ the radius that will ↓ the inertia causing less resistance to movement making it easier to move faster

Question 23

what is the equation of human moments of inertai

Answer 23

I= sum of mk^2

k= radius of gyration the object mass distribution with respect to a given axis of rotation

Question 24

how does moment of inertia and linear velocity connect

Answer 24

longer radius = higher linear velocity (↑lenght, MOI↑)

↑ angular inertia-= more difficult to accelerate the object angularyly to keeep the same angular V

Question 25

What is angular momentum

Answer 25

(H)
-quantity of angular motion possessed by a body

H=Iw
H=mk^2w

I- inertia
w- angular velocity

Question 26

how to find total angular momentum

Answer 26

for multisegmented object the angular momentum is the sum of the angular momenta of the individual body segments

H= sum (Iw + mr^2w)

so it is the sum of all the local terms Iw of the segment
and the remote term mr^2w of the entire body

Question 27

What is the conservation of angular momentum

Answer 27

• the principle of conservation
• the body MOI is variable and can be changed by altering limb positions
• w of the body also changes to conserve M and accommodate changes in moment of inertia

H1=H2 or

(mk^2w)1= (mk^2w)

Question 28

principle of conservation of H

Answer 28

the total angular momentum of a given system remain constant in the absence of external torques

– when in the air with no external torques you can…
1 transfer angular velocity form on epart of th body to the other
2 change the total body axis of rotation

Question 29

what happens is the tradeoff with H and inertia and w

Answer 29

tucked position= small I and large w

extended position= large I, and small w

Question 30

What is the angular law of acceleration

Answer 30

a net torque caused angular accelertion of a boyd that is proportional to the torque inversely proportional to the body moment of inertia
- if the E T action on a object do not sum to 0the objet will experience an w i the direction fo the net torque
T=Ix or T=mk^2x

Question 31

Net T and H

Answer 31

the change in angular momentum of an object is proportional to the next external T and the change in direction. the net external T is proportional to hte rate of change of the H
sum of T= change in H

large T= large and quick change in H
small T= small and slwo change in H

Question 32

what is angular impulse

Answer 32

the product of T and the time interval over which the torque acts

Tt=(Iw)2-(Iw)1

-H is required for total body rotation executed in the air primarily derived from the angular impulse created by the reaction force of the support surface during take off

Question 33

what is angular law of reaction

Answer 33

for every angular action there is an equal and opposite angular reaction

• when one body exerts a T on a second the second body exerts a reaction T that is equal in magnitude and opposite in direction on the first body

Question 34

why would a tightrope walker use a pole

Answer 34

this would increase K that would increase I so it would be hard to move

-↑ MOI and ↓ CoG =↑ stabillity

Question 35

linear kinematic quantities and equation

Answer 35

mass= m
force = F
momentum= M=mv
Impulse= Ft=mv

Question 36

angular kinematic quantities and equations

Answer 36

moment of Inertia= ( I=mk^2)
Torque= ( T=Fd)
Angular momentum= (H=mk^2w)
Angular impulse= (Fdt)

Question 37

read over the last slide of 5b

Answer 37

this is a bunch of equations