3.2.2.4 Angular motion

Question 1

motion is linear or angular?

Answer 1

dependant on direction of application of force in relation to COM

Question 2

linear motion

Answer 2

apply force through COM e.g. snooker (line of application pass through COM = resulting motion = linear) = DIRECT FORCE (reaction force from ground)

Question 3

angular motion

Answer 3

force whose line of application passes outside COM of body = resulting motion = angular e.g. high jump
ECCENTRIC FORCE

Question 4

e.g. back somersault

Answer 4

eccentric force = angular motion = take off
enough vertical force= body into air for sufficient time
-control size and direction of GRF
correct positioning of body at take off = GRF = aimed up & in front of COM

Question 5

moment of force & torque

Answer 5

describe turning effect produced by a force 
acts eccentrically (to 1 side of) to an axis of rotation 
moment = f x d 
d= distance from axis of rotation

Question 6

angular displacement

Answer 6

smallest change in angle between start and finish angle should be measured in radians

Question 7

1 radian

Answer 7

57.3 degrees

Question 8

angular velocity

Answer 8

angle turned through per second
rotational speed of object and axis about rotating
ω = angular displacement divided by time taken (rad/s)

Question 9

ω

Answer 9

omega

angular velocity

Question 10

3 sports rates of spin apply to

Answer 10

1 tumbling gymnast
2 spinning skates
3 trampolinist (tucked somersaults)

Question 11

angular acceleration

Answer 11

rate of change of angular velocity (rad/s squared)

change of angular velocity divided by time taken
ω2 - ω1 divided by t

used when rates of spin increase or decrease

Question 12

newtons 1st law

Answer 12

angular velocity remain same provided no external torque acts
angular momentum remains same (conserved)

Question 13

newtons 2nd law

Answer 13

rate of change of angular momentum of body = proportional to torque causing it & change takes place in direction in which torque acts

Question 14

newtons 3rd law

Answer 14

torque is applied from 1 body to another = second body will exert equal and opposite torque on first body

Question 15

moment of inertia (I)

Answer 15

= mass for rotating systems

object rotating large I = large torque = change AV

small I = small moments of force/torque change AV

Question 16

moment of inertia depends on?

Answer 16

1. spread of mass away from axis of spin (body shape)

spread out (arms wide) = bigger  
kg/m^2 

mass away from axis of rotation increase I (picks/tucks = reduce I)

Question 17

conservation of angular momentum (AM)

Answer 17

flight = no external torque
AM spinning body = same (no external torque)
spinning/twisting/tumbling = keep value of H once movement begun
I changes =ω also changes keep H the same
I increases ω decreases rate of spin gets less
only exactly true if body has no contact with surroundings

Question 18

angular momentum (H)

Answer 18

moment of inertia x angular velocity

I x ω

Question 19

spinning skater example linking to moment of inertia

Answer 19

arms wide = I large = slow spin

arms narrow = I small = spin quick

Question 20

tumbling gymnast example relating to moment of inertia

Answer 20

body position open I large = spin slow

closed/tucked = I small = spin quick

Question 21

relationship between centre of mass and application of force

Answer 21

tucking decrease I (mass closer axis of rotation = easier rotate) angular velocity increases
rotate faster = ensure performer = more time for landing

Question 22

eccentric force

Answer 22

off centre force