Circular Motion - Science Theater 016

[sciencetheater]

Lets see if we can clarify some things to help conclude the ongoing discussion.

Centrifugal force (a force pushing outward from the center) --> a misunderstanding of physics

Centripetal force (the force pulling toward the center) --> the sum of all forces on an object, which makes it travel in a circle

In a sense, a centripetal force doesn't exist - it isn't one of the four (three) fundamental forces in the universe. On the other hand, it IS a concept that exists that describes a net force.

[MrRJames73]

How do you go from being wrong about centripetal and centrifugal forces to talking about curving space? Stop trying to teach physics, give drake university their degree back, and go to a real school to learn about physics.. such as BSHU. You're teaching these young kids the wrong things which they will commit to memory. O and get some new clothes.. may I suggest Nike?

Your shit has just been killed

[NinjaB12]

Yeah sorry, centrifugal forces do not exist. For example, when someone is turning the car, you may feel like you're moving outward, towards the door. In actuality, you want to keep going in the same direction, so you and the door end up colliding.

[justforfun22111]

@feliztex centrifugal forces are not real. a centrifugal force is an outward force you feel while you are rotating. you only think there is a force because of the inertial reference frames. they are not real. and you cant curve space time with them!

[MrRJames73]

You do know that centrifugal force is fake right? Centrifugal force is what you feel being acted on by centripetal force. And the definition of centripetal force is "center-seeking" force?

[llamadude314]

@feliztex You seem to have your forces a bit screwed up. Centrifugal forces is not real, it is just a misconception of real forces and laws in action. Here is an example, going down with a high velocity on a roller coaster and then the cart of the roller coaster changes direction to go up on another hill. During the change in direction, you would feel as though you are being pushed into the ground and that is what some people think is centrifugal force or g force. This is completely wrong.

[llamadude314]

@llamadude314 Centrifugal force is just Newton's Laws of Motion. Newton's first law states that an object in motion will stay in motion. During the fall in the roller coaster, the human body is going down. Now, the roller coaster will change direction, but while the roller coaster changes direction, the human body still wants to move down which causes the feeling of the "g force", but in reality, there really is no force causing that feeling, just the body wanting to stay in the same direction.

[llamadude314]

@llamadude314 So centrifugal force is not real. The object that is in some rotational movement just wants to stay in the same direction, but since it is in some rotational movement, the direction is constantly changing.

[great112211]

@feliztex Umm, guess what centrifugal forces are fictitious there's really no debating that (And you're going to receive more comments like this i'm warning you now). You think the centrifugal force acts on the objects in the frame, well it doesn't, it only feels like it does, but what real force can you associate with centrifugal force? I understand we don't know everything about our world, but centrifugal forces will stay fictitious for a long time to come.

[great112211]

@great112211 Oh and centripetal forces is a real force, since it can be associated with real forces, you're right to think that there really is no such thing as the centripetal force, it's just a name given to any force that points towards the center.

[danish9t5]

wonderful!!!!!!!



[LFchinatown]

Your ties are always awesome

[feliztex]

Very nice experiment with the candle! It demonstrates that centrifugal forces are real and that the centripetal force you talk about is in fact fictitious: the candle movement is its inertial reaction to the centrifugal force outwards. It is obvious now. Put the same candle inside a car and start accelerating the car. You will see the light of the candle pointing the opposite direction of the real force. Thank you! And forget centripetal accelerations do to rotating objects.

[sciencetheater]

@feliztex To be precise, the flame (not the light) of the candle will point in the opposite direction of the real force. This is because the flame (and associated hot gases) is lighter than the air around it and will move in the opposite direction of the force. Candle flames typically burn upwards - because gravity is usually downwards. In the same way, the candle flame points to the center of the circle, because the centripetal force is away from the center.

[feliztex]

@sciencetheater: :)) yes, the flame... but I think we both are wrong. I mean, not 100% correct. I more sure now: the circular restriction of movement creates a fictitious centriPetal force which provokes a real force in reaction: the centriFugal force. The flame inclines in the direction of the "action" while the basis of the candle is pushed to out of the centre. The flame will always point in the direction of the action (even if the action is fictitious). Se this: /watch?v=KWvJHdNaPV4

[feliztex]

@sciencetheater: :)) so, it seems we can create a real force by simply forcing a curvature in the space... nice, hm? Einstein thought on this, for sure. Centrifugal forces are real. Fortunately.

[sciencetheater]

@feliztex Hmm, if you're going to curve space, I'm not going to debate what will happen... sounds a bit deeper into the theoretical side of things than I'm interested in delving... However, if you are on a circular space ship that rotates to create artificial gravity, note that there is no force pushing you DOWN into the ground (centrifugal) only a force of the ground pushing UP on you (centripetal.)

[feliztex]

@sciencetheater; hi, if you are really interested to understand what I mean I invite you to Google: "Apparently Deriving Fictitious Forces [free]". We are all still very confused with what our world is, don't doubt... regards.

[Farenzil]

@sciencetheater. if u got to centripetal forces, one that spins the flame and one that spins the platform it stands on. What direction will the flame point then?(If the circular motion is the same direction?)

[Farenzil]

@sciencetheater *two centripetal forces.

[thelasttimeitried]

An object traveling in a straight line will continue traveling on that course until acted upon by another force. When a force is applied perpendicular to the direction of travel and you deflect the object without changing its speed. Keep pushing with a constant force perpendicular to the direction of travel (in the same plane, etc), and it ends up going in a circle. Worrying about 'up/down/in/out' just muddles the picture.

[SONGSBYMAX]

Ether...

[Narkarina]

1:34 if that were true we would be walking around with major headaches..

[RJonStreetz]

@Narkarina you are a headache to science LOL

[lekunberriko1]

very nice tie.

[Dellster13]

Hi, any ideas how to convince me that what is shown here is true ... e.g i think like this: when in circular motion the force is acting away from the circle hence why we fly away from the circle ! But apparently this isn't true and i cant get my head around it !

[sciencetheater]

@Dellster13 put a ball on a merry go round, and watch what it does when it flies off... it will fly off and head out tangent to the circle... (Note, use a big enough circle so you can compare its path to the center of the circle.) Or think of a car going around a big wide corner. If you let go of a ball out the window it will fly "forward" (true, it might look like it will fall behind you if you're going fast) and not straight sideways...

[abztehbabz]

thanks, this really helped

[hobomnky]

the way i see it the denser air is being pushed outward and the hot lighter air is then forced more towards the middle

[sciencetheater]

@hobomnky Yes, as long as you keep in mind it isn't technically "outward", the bottle is being pulled inward... :) The denser air is just trying to not move...

[hobomnky]

@sciencetheater can u explain y

cuz we r basically saying the same thing but looking at it from 2 different points of view

[sciencetheater]

@hobomnky In order "move" the air in the jar in a circle, it has to be pushed towards the middle of the circle. The jar pushes the air inwards towards the center (and thus the air experiences an accelleration in that direction). Accelleration and gravity are indistinguishable to anyone experiencing them, so the air in the jar "feels" like there is gravity pulling on it from the outside of the circle. Thus the denser air will settle to the outside edge of the jar.

[manofaction2828]

Dude, I love this stuff. You're making concepts I already understood so much cooler. Subscribing

[carvingmadness]

Still cannot grasp concept that the center is "pulling" in all of the demonstrations. It appears as though you are only "holding" the items, not pulling them. May take some time. Excellent presentation nevertheless. Thanks

[sciencetheater]

@carvingmadness The key thing to keep in mind is that _something_ is making a force towards the middle. Think of a ball twirled on a string. It only works if the string is on the center side of the ball. You can't twirl a ball in a circle with the string on the outside.

Make a ping-pong ball go in a circle by surrounding it with people. If you start the ball rolling on the edge, all the people blow toward the middle to make it go in a circle.

[carvingmadness]

very nice explanation. plan to revisit this site again in order to better absorb the whole concept. a bit difficult to understand as to "why" it does what it does, but will review. thank you.

[xxxcoolboyxxx]

Your videos are so greatt!

[mxs703]

okay so what about when an object is spinning vertically like in ur demo... will the force being exerted at the top be different from the bottom

[sciencetheater]

For the wineglass... the force exerted by the string is greater at the bottom than the top, HOWEVER, the NET force is the same at the top and bottom (the NET force is constant - in magnitude - when something is moving in a circle. vertical or horizontal.)

At the top the string and gravity pull down on the glass. At the bottom, gravity pulls down and the string has to pull up against gravity AND add in more force to create the net force.

[mxs703]

ok cool thanks

[jello07032]

please go on and make more videos you´re so cool and i love science

[planetrob555]

Looks like you are accomplishing what teachers should be trying to accomplish. Inquisitive people are engaged in conversation about something, in this case, science.

So, my hat's off to you, sir.

...............rob

[sciencetheater]

Thanks for watching and commenting!

-Dr. C

[Merdam9]

Where did you buy that DNA tie??

[sciencetheater]

A gift from my parents I believe.

[ZeroMinima]

With this one your are actually the coolest man on earth!!! Dude

[cmajorutube2010]

does this has to do with action reaction law of motion? bcz u mentioned the object being pulled to the centre but what i see is the object is trying to move outwards.. so does this mean tat the action is pulling it inwards and the reaction is pulling it outwards?

[sciencetheater]

That is close. A ball on a string going around in a circle is really trying to go in a straight line, but the string pulls it in toward the center to make it go in a circle. By Newton's 3rd law (action/reaction) the ball must then be applying a force on the string.

The important thing to keep in mind is that there is NO force on the ball pulling out, just pulling it in. (The ball pulls out on the string, the string pulls in on the ball.)

[oooowwwwdddd]

I don't understand that. It seems that the ball is being pulled outward by centrifugal force and the string is stopping it from traveling away from it. The string isn't necessarily pulling the ball inward but just keeping it from traveling outward.

And, can you produce artificial gravity in space inside a spinning cylinder or is that an unproven theory?

[sciencetheater]

There is no centrifugal force. If you let go of the string, the ball goes straight (not outwards, so if you were twirling vertically, and let go at the top, the ball would fly straight forwards not straight up). To make something travel in a circle, you have to pull it towards the center of the circle.

[sciencetheater]

You can make "artificial gravity" by spinning a cylinder, it will feel like gravity, etc... In fact, even if the cylinder is stopped, but you run around on the inside surface, you will feel like its gravity... you just have to have the circular movement...

[edwardmanboy]

by the way u sed lean on ur info thing instead of learn =] just saying nice video lol

[edwardmanboy]

nice

[edtronic]

you are cool