ShmoopTube

00:00

Hurry And here's your shmoop du jour Brought to you

00:05

by a ball tied to a stick with a string

00:07

Yep because without that how are the mice gonna play

00:10

tether ball if they do falling diagram right balls attached

00:14

to a string with a string assuming the ball is

00:17

spun with equal force what will happen to the velocity

00:21

of the ball if the length of the string is

00:23

have And here the potential answers All right equal forces

00:27

Well that's Really important Okay so let's think about angular

00:31

momenta Angular momentum is the amount of rotation object has

00:35

mathematically speaking Angular momentum is the product of mass velocity

00:39

and distance from the centre which we can think of

00:41

as the objects radius good word and the our baby

00:46

And we know once mo mentum starts it won't stop

00:49

or change until something acts to change it that's the

00:52

law of conservation of momentum That's what nunes first laws

00:56

all about an object in motion stays in motion until

00:59

something acts on it and rotating or orbiting objects have

01:03

their own law of conservation of angular momentum The idea

01:06

is the same No angular momentum doesn't change unless it

01:10

has To just like us with socks way Don't change

01:13

him unless we have to get pretty pungent by your

01:16

laundry day So if an object momentum doesn't change unless

01:19

something acts upon it well what happens if the object

01:22

itself changes We'll answer that by talking about our favorite

01:26

sport figure skating We get so hyped about the winter

01:29

olympics and every four years you start dressing like ice

01:31

dancers just to get into the spirit All right well

01:34

we especially love when a figure skater starts twirling around

01:37

and then she goes faster and faster and we get

01:39

dizzy just looking at her The reason she picks up

01:42

speed is because she changes her radius She starts spinning

01:45

with a certain momentum and she has her arms out

01:48

wide like that A speeder spin She brings her arms

01:51

and is close to her body She can decreasing her

01:54

radius Her velocity than increases that's because the angular momentum

02:00

has to remain the same and her mass isn't changing

02:03

So if one part of the equation decreases another part

02:07

has to increase So now let's take a look at

02:09

our question If the force applied to the ball is

02:11

the same that means the angular momentum has to be

02:15

the same too So if we cut the length in

02:17

half the rest of the equation has to double The

02:20

mass of the ball isn't changing so the velocity will

02:23

have to double means going to spin around twice as

02:25

fast It means the right answer is c Now we're

02:28

going to get back to our rodent tether ball match

02:30

It's super cute toe watch But sometimes steve the mouth 00:02:33.603 --> [endTime] can be a real sore loser

Full Transcript