Hi, I'm Dianna.
You're watching Physics Girl.
And welcome to the last part of physics riddles with my friend,
the Queen of Imperfect Robots, Simone Giertz.
If You haven't seen the last part,
I've got a link in the description and a card
and, you know, all the good stuff.
Here's a recap of the second riddle and the answer.
All right, you're sitting in a boat holding a rock,
and it's a rock that will sink in water.
You throw it off of the boat into the water, and it sinks.
Does the water level go up, go down, or stay the same?
So I'm thinking of when you have it in the boat,
it's the weight of the rock that matters because that's
like what's weighing the boat down and pressing
the water out.
Displacing some water.
Yeah, displacing some water.
But when you throw it off, it's the volume
of the rock that matters.
Because so now the volume is displacing the water.
Yes.
I mean if it's one of those, you know,
those rocks that float like [INAUDIBLE] in Swedish.
But I did say that it sinks.
OK, it sinks.
Yeah, so I see what you're getting at.
But part of the important setup of the question
is that the rock sinks.
The weight of the stone is going
to displace more water than the volume of it.
And that is because--
that's because it's more dense than the water.
I like how you're thinking.
Yeah, no.
So I think that the water level is gonna sink.
Because if you just have a barrel of water
or a mass of water, you would have it in the boat.
And then you'd throw it on the side, that wouldn't affect it
because that same volume of water weighs as much as the--
As you displaced.
Yeah, but the difference is that the rock is heavier.
It's more dense than water.
Yeah.
Is that correct?
Yes!
Yeah!
High five!
Yeah.
That was exactly correct reasoning.
Thank you.
I actually make a video about this one.
And the way that I like to remember it is I
think of a really extreme case.
So if you have like a super, super, super heavy rock,
but it's really small--
Yeah.
So you imagine a rock made out of black hole material.
If you put that in your boat, your boat is going to-- it's
going to sink really far down into the water,
and that will push the water level up really far.
And then when you throw it overboard,
the boat will come way far back up.
And the water level will go down because it
won't displace much water once it falls in the water.
I feel like overall that's such a good approach to problem
solving where we're just taking it to one of the extremes
and being like does this reasoning makes
sense in the extreme cases.
Second question--
Oh there's more.
There's more.
What is the difference between a servo motor and a DC
motor in how it functions and how you, as a user, use it?
Well, I'm going to guess that a DC motor,
you put direct current through it.
OK, a DC motor-- no, I have no idea.
Mostly I--
I have failed so hard.
No, no, no, you're doing good.
Take my star away.
No, keep your star.
Don't-- they're non-returnable.
But what's the difference, I mean
there are a lot of technical differences between servo
motors and DC motors.
But for the use case of it, DC motors
are very easy to control the velocity of them
or the speed of them, so how fast they spin.
Whereas servo motors, you control the precision.
So a servo motor, you would want
to use in one of those claws that goes and picks up
the animals, like you want it to be in a specific location.
But then you don't want a good claw that actually picks up
the animals because you don't want any of the children
to win any prizes.
Because you just hate the world.
Because you're terrible corporate monsters.
No.
We should build a claw machine for the greater good
that picks it up every time.
Everybody wins.
That is a fantastic idea.
But I have a feeling that if you tried to do it,
you'd be like really well-intentioned,
and you would end up beheading the toy.
That would be such a fun project.
Having a claw machine, it actually got it.
But then it just like completely crumples everything
and gives it to you.
I might have to build that.
I'm getting--
Just remember that it started right here.
This is payback time.
You might have this one.
I always confuse the two.
It's a [INAUDIBLE] question.
What's the difference between a bit and a byte?
Oh, I confuse them as well.
So one of them is eight of the other.
Umm-hmm.
Which one is which?
A bit is smaller and a byte is larger.
So a byte is 8 bits.
Am I right?
You got it.
Thank you!
[INAUDIBLE] forehead.
All over your clothes.
I got--
If we go out, what do you think people would
think that we had just gone to?
I don't know, maybe to the dentist.
And we had to pull out a lot of teeth.
I was thinking like we taught first graders.
And we were like, you can put these wherever you want.
And they were like--
Just put it on your body.
Last question, bonus question.
Is this when I level up in my physics game?
This is when you level up.
So you have two sticks.
It takes an hour to burn each stick.
If you wanted to time an hour, for example,
you could just burn the whole stick.
How do you time 45 minutes?
And they burn at varying rates, so you couldn't just
like mark it in half and say, OK, it's burned halfway
so now it's been.
Along the length of the stick, it burns at different rates.
So you couldn't just gauge when it's halfway
or when it's like 3/4 of the way.
Two sticks.
You say, Alexa set a timer for 45 minutes.
45 minutes, starting now.
In 45 minutes, we're going to be like--
Ooh, you can burn them from both ends.
[INAUDIBLE] Ooh, because then you can time half an hour.
Burn one from both ends or like--
[INAUDIBLE] need more than a half hour.
I got you girl.
I'll only be 45 minutes late.
Ooh, what if you--
OK.
Ahh!
OK, I got it.
You burn one of them from both ends, one from one end.
When the one that burns from both ends is burnt out,
you turn the other end of the longer one.
Girl!
Yeah?
Yeah.
[INAUDIBLE] You will still acknowledge that you know me
in public.
Where's your gold star?
Oh yeah, [INAUDIBLE] I got a gold star.
I got a gold star.
Yeah, you get this one.
It's a little bit--
Oh, but that's OK.
Yeah, it's right in the middle.
That was amazing.
Not that I expected you to do poorly.
It's just like I put you on the spot in front of a camera
and ask you some tough questions.
Good job.
Pound it.
Thank you.
Alligator.
[LAUGHTER]
High five.
Time to end this video.
Should I do it [INAUDIBLE]
We're losing it.
We need to wrap this back together, this bag of crazy.
Thank you so much, Simone, for letting
me put you through that.
Thanks for having me.
This was fun.
It was super fun.
Yeah, I feel the physics part of my brain being like--
It's blossoming, just a little.
I hope some day to work on a robot with you.
Yeah.
I've got plenty of ideas.
And thank you so much for watching this madness.
Subscribe if you want more physics videos.
Usually there are more physicsy, but this was fun.
And hit the notification button, I guess.
They do that.
People do that, if you want more notifications.
I didn't know you could do that.
Yeah.
YouTube keeps changing things up.
I'll hit the notification button on your channel.
You should get notified when they have videos.
No, no, I'd love to get notified.
And check out Simone's channel.
And happy physics-ing!
It feels weird because we're at your channel,
but we're at my house.
We're at your house.
Yeah, it's a way to be somebody's guest.
You're just like coming into their house and being like,
no, this is my show.
[LAUGHTER]
Tearing up.
I don't think I'm going to be able to get
through filming this because--
No!
I can't look at you.
How are we ever--
I don't even know what's funny.
Your grandma is Italian.