There's a difference between centripetal and centrifugal.

Centripetal force:

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All accelerations are caused by a net force acting on an object.  In the case of an object moving in a circular path, the net force is a special force called the centripetal force (not centrifugal!).   Centripetal is Latin for “center seeking”.  So a centripetal force is a center seeking force which means that the force is always directed toward the center of the circle.  Without this force, an object will simply continue moving in straight line motion.


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Centrifugal force represents the effects of inertia that arise in connection with rotation and which are experienced as an outward force away from the center of rotation.

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Physics Day 4: Non-Fundamental Forces

Source: http://www.school-for-champions.com/science/friction.htm#.VWd13mRViko

Now, usually when we think of force, we think of forces that arise from combinations of fundamental forces. We touched briefly on them last week - the normal force being an important force that makes everyday life possible. However, there are a lot of non-fundamental forces that we experience in everyday life that are important to talk about. There’s normal, friction, tension, elastic, pressure, drag, stress; then there are forces associated with rotation called torques such as centripetal force; then there’s the difference between conservative and nonconservative forces. Needles to say, it’s complicated. 

Friction is the force that opposes motion. So in the above example, you’re pushing on a box - friction is what keeps that box from just spiraling forward. Friction is caused the contact between two surfaces and can happen between any state of matter - solids, fluids, you name it. There are multiple types of friction: dry friction occurs between two solid surfaces in contact and is what we typically think of when we think of friction; fluid friction between two fluids (liquid or air) moving against each other; lubricated friction where a fluid separates two solids; skin friction where a fluid moves across the surface of a body; and internal friction, the friction between elements within a material that affect each other when such a material is deformed. Frictional force actually converts kinetic energy into thermal energy - the motion of one object turns into heat. 

Tension is the force when a string, cable, chain, or something similar is exerting a pulling force. Tension occurs when atoms and molecules in these materials are pulled apart from one another which actually causes them to gain potential energy. It’s opposite is compression, when a material is pushed together causing all the atoms and molecules to come closer together. Tension really describes a grouping of forces that all act similarly. System involving tension usually have two possibilities - either its acceleration is zero and the system is in equilibrium, or the system is accelerating (like a yo yo) and there is a force present in the system. 

The elastic force involves solid materials that return to their original shape after being deformed - or, not returning to their original shape as the case may be. The more elastic a material is, the more able it is to return to its original shape - however, perfectly elastic materials are few and far between. Usually when elasticity is thought of it’s in relation to springs - an ideal spring is massless, frictionless, unbreakable, and infinitely stretchable, which of course does not exist. But if it did, they’d exert pushing forces when contracted and pulling when extended proportional to the amount the spring was moved from equilibrium. 

Pressure is the force that is applied perpendicular to the surface of an object, given per unit area over which the force is distributed. Pressure thus isn’t actually a force but a measure of how a force is applied, and is important to consider in many aspects of science - from how an engine works to how rocks are changed inside the Earth. Stress, on the other hand, is a measure of the forces exerted by the particles neighboring each other in one material. Strain is a measure of how much that material stress. Stress, strain and pressure all come together and are used by everyone from engineers to architects to design materials that will not deform under the forces exerted by their environments. 

Torques are forces that cause extended objects to rotate - the spokes of a wheel attached to the center, a ceiling fan, and a planet rotating around the sun. Torque is, thus, the rotational equivalent of force - a whole branch of physics actually studies the properties of matter, energy and motion in relation to rotational objects, which have to be studied differently than those objects moving in non-rotational contexts. Centripetal force is one of the forces in question and involves objects that are in circular motion, such as those described above. 

Now, conservative forces versus nonconservative forces! A conservative force is one that acts on a closed system that only allows energy to convert between kinetic and potential forms - this means that mechanical energy within the system is conserved. There are actually a lot of conservative forces - gravity, electromagnetic and spring forces only have to do with the mechanical energy of a system. Nonconservative forces, therefore, allow for energy to be converted into other forms, such as heat - these include friction, tension, compression, and drag. 

Forces are complicated, everywhere, and affect how we do pretty much everything - and have to do with the motion of objects. So how do we talk about motion? Well, with Newton’s laws - which will be our topic next week. 

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River Orders and Patterns

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Streams and rivers go in very specific orders. The most common form of labeling them is with the Strahler classification system. The smallest tributaries are referred to as first-order streams while the largest river is a twelfth order waterway. First through third order streams are labeled headwater. 80% of the Earth’s waterways are headwater.

When two first order streams join, it forms a second order stream. When two second order streams meet, it creates a third order stream. However, when a first order stream joins a second order, the stream remains as a second order. It does not become a third. When a stream is assigned an order, the number refers to the lowermost section of the stream.

There is a change from the point of origin or headwater to their mouths or where they empty into a larger body of water. The depth, width, and velocity gradually change as well as the amount of water exiting as water approaches the mouth of large rivers. This is known as the River Continuum Concept.

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There are also many patterns of river, most, but not all, shown here. This is a general shape for each. Radial and centripetal tend to look like spokes on a bicycle wheel. Deranged is mostly random seeming as the name implies. Rectangular also speaks for itself. Trellis looks somewhat parallel. Dendritic is leaf-looking, mostly. Annular, not shown above, is a river form which is somewhat circular. 

Centripetal Force & Acceleration

Centripetal force is a force that is perpendicular to motion as shown in this diagram

These diagrams show the basics of centripetal force. There are a few things you should notice:

~Even thought the object is following a curved path, both v1 and v2 are straight lines. Why? An object will always want to go in  a straight line , unless acted on by an unbalanced force. Here’s an example: think about when you are in a car and the driver makes a turn. You feel like you are being pushed against the door of the car. Actually, what is happening is that you want to still go in a straight line, but the car turns and pushes your body into the new direction.

~Centripetal force (Fc) is always towards the center of the circle.

~As seen in the car diagram, the object is pushed right, to the center, to go left and vice versa.

*NOTE- Even if an object is just turning it is still considered circular motion.

In this picture, the string is creating the Fc, pulling perpendicularly to the object to create a circle. 

When Fc is continuously applied, it is constantly “tapping” the velocity so that it changes direction ever so slightly and creates a circle.

There is no outward force, otherwise the object would go in a straight line.

Now, what would happen if someone cut the string? Well, there would be no more Fc to “tap” the velocity. So whatever direction the velocity was in at the precise moment the string was cut would be the direction that the object would fly, in a straight line.

Think about this:

What is causing the Fc of a satellite orbiting Earth?

The Fg of Earth.

What is causing the Fc of a car turning?

The friction of the road.

What is causing the Fc of laundry spinning in a washing machine?

The walls of the machine. 

Now here is another thing to remember:

Centripetal acceleration (ac) is always in the same direction as Fc. 

How do you find the ac? Another formula! yay!

Let’s look at the units.

 the squared in the numerator and the m in the denominator then cancel leaving you with

  which is the units used for acceleration (ac).

a few cool people for your consideration.

1. centripetal ; my boo. if you don’t follow her something is wrong with you. she has a ton of other cool blogs too (a one for color images and some cool collabs)– specifically flash-bangs which is some fuckin quality shit let me tell you.

2. goodbyeoldengland ; another quality blog with an absolute darling behind the keyboard. black and white, male model packed, absolutely gorgeous. i’m not sure what else to say other than follow her or i’ll shit on your doorstep.

3. superjunkhead ; probably one of my idol blogs negl. i reblog practically everything they post cause it’s fucking brilliant and top notch– stuff i don’t really see already floating around or just edited and reposted. i look forward to their posts a lot and you know what you should too.

4. heretic-vii ; pretty much take what i said above and copy and paste here. another blog that really inspires me; always seems to find new and interesting stuff. also in flash-bangs (linked above) so you know they’re the shit.

5. shitfuckcockballs ; this is a more eclectic blog than the others (which are primarily fashion/black and white) aaaand i’m pretty sure i’ve been following them since the dawn of time. s/he posts all over the place (i think he? i’m not sure? listen whatever shut up) basically the point is i dig it and you should dig it if you know what’s good for you. it’ll spice up your dash.

k that’s the end of my spontaneous whatever this is. i picked only five cause well i’m lazy and it’s nearly 3 am but rest assured if i follow you i probably really like you and mouthbreathe all over your shit like a total creep. cool beans.


Hammer throwers uses a lot of centripetal force.

The chain is what provides the Fc.

They continuously spin around to keep applying the Fc.

They know to release at exactly the moment when the velocity it pointed out of the hole in the fence so that the hammer flies in that direction.


so, i kind of loathe promo posts clogging up dashboards and i don’t honestly talk personally on here a lot but i’ve had a lot of spectacular people come my way and though i’ve limited myself to five people now, i might do one of these again later to show how much i appreciate most of you guys. so here, in no particular order:

1. xabuton – terry schiefer’s tumblr, he posts amazing shit, guys. seriously. not only that, he makes probably the most beautiful jewelry i’ve ever laid eyes on. he’s always really kind to people that talk to him and he’s an all around super nice guy with a great eye for fashion.

2. asyllum – i can’t remember who on my dash linked her but i should find them and kiss them on the mouth because i adore her blog so much. it’s dark and interesting and incredibly unique. maybe not everyone’s cup of tea, but give it a try and wait it out. she grows on you.

3. gthegentleman – i followed him on a whim one day and i haven’t regretted it since. he’s got incredible style and is probably one of my top reblogged tumblrs. such a nice guy, too. definitely give him a try if you want to class up your dash or just want to talk to a real gentleman.

4. centripetal – my darling win. one of my best friends in the whole world. there’s really nothing i can say to sum up how fucking fabulous she and her tumblr are mostly because i’m lazy but also because it’s hard to put into words how much you admire someone as much as i admire her. honestly, just go take a look for yourself. you’ll be stunned, i promise.

5. finefools – this girl is hilarious and her tumblr is actually one of my favorites on here. i don’t honestly follow many blogs that aren’t fashion related on here anymore but i make it a point to keep her around because she makes me laugh and she’s got a really unique sense of aesthetic and style. and hey, she likes chico, how can you go wrong?

there you go. go forth and be merry.