# hollyferg

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• Birthday 08/23/1996

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1. ## the physics behind taking your physics test!

so much physics my brain hurts ahh
2. ## The Physics of Walking.

Walking is something that we do every day, without thinking about it. Its seems very simple and straight forward. You just put one foot in front of the other and you move. But it is kind of complicated. It has a lot to do with forces. Newton's laws of motion are involved. So what do forces have to do with walking? Newton's third law states that every action has an equal and opposite reaction. This is relevant to walking because when you put your foot on the ground, you are applying a force to it. In doing this, the ground also actually applies an equal force onto your foot, in the opposite direction, pushing you forward. When running, you tend to take longer strides because you are applying a larger force to the ground, so the ground must apply a larger force onto your body. When a larger force is applied to your foot, you go farther, taking a longer step. Another law of motion that is at work is Newton's first law of motion. An object in motion stays moving, and an object at rests stays at rest unless an outside force acts on it. If people didn't apply forces to the ground, they obviously wouldn't move. This is because the ground then doesn't apply a force to the persons foot. They would stay at rest. But also, if it weren't for gravity, we would all float up into space the second we took one step. This is because the ground applies a force onto us, so we are set into motion. Gravity keeps this force from pushing us all the way into space. (there is also centrifugal force that wants to fly people off of the planet, but ehh.)
3. ## Space Elevators?

that would be so awesome! but still really scary haha
4. ## Waves at Concerts!

its pretty cool how sound can bend and still reach you even if stuff is blocking the waves ^^
5. ## Static Electricity!

Weird things can happen in balloons. They're affected a lot by static electricity. This is why it will stick to a wall or your clothes after it has been rubbed against something else, like your hair. This happens because of the charge of the balloon and whatever you're trying to stick it to. Something that is charged negatively will stick to something that is positively charged. If you rub a balloon against your head, it becomes negatively charged because it gains electrons from your hair. This picture shows what happens when you put a charged balloon on a wall. The balloon is negatively charged. When the balloon comes in contact with the wall, the wall and the balloon both become polarized. The negative particles in the balloon are attracted to the positive particles in the wall, and also push the negative ones in the wall away, so they stick and the balloon appears to be floating all by itself. Another thing that can happen is that two balloons can repel each other. If two different balloons are rubbed against your hair or clothes or anything else that loses electrons, they will both become negatively charged by gaining electrons. If they are brought near each other, they will want to repel. But it my opinion, it is more fun to see balloons stick to things. Like this cat.
6. ## Boxing!

i never thought about how potential energy relates to this, it's pretty cool
7. ## Pump up the Energy!

i have always been suspicious that energy drinks are terrible. hm.
8. ## The Earth is a Giant Magnet

Have you ever wondered how compasses work? How they always point the same direction? It's because the Earth is just a big magnet! Compasses are magnetized so they always point north, no matter where you are on the Earth. But why does this happen? That is because the north side of the compass is attracted to the geographic North pole. This shouldn't make sense because opposites attract, so two north poles of a magnet should repel each other. This can be easily explained- the "North Pole" is really the magnetic south pole of the Earth. So when a compass is pointing north, it is really pointing to the south end of the Earth. However, compasses can be easily interfered with. They're just sensitive magnets, so if another magnet comes close to the compass, it will point towards the south end of the other magnet, and no longer point to the Earth's North Pole!
9. ## Physics of Sailing

i always wondered about the sail. it seems so confusing!
10. ## The Physics of a Concert

i didn't realize how many waves there were in a place like that! with all the lights and the music too
11. ## Physics of Trampolines

Everyone likes trampolines. But how do they even work? It's all about energy, and at the same time, proves Newton's laws of motion. Potential energy (PE) and kinetic energy (KE) are the reason trampolines allow you to jump higher than you can on flat ground. One type of potential energy that is involved with trampolines is the potential energy stored in springs. Another type of energy is gravitational potential energy. There is also kinetic energy because you are moving. The equation that connects potential and kinetic energy to find total energy (E) is: E=PE+KE+Q The total energy of the person jumping on a trampoline equals all of the potential energy (both the spring and gravitational potential), plus the kinetic energy. Q is internal energy, which isn't really important here. Other equations needed to understand the forces and energy of trampolines are: PE=mgh This used to find the potential energy due to gravity. You multiply the mass of the object (or person in this case), by the height they are from the ground, by g, acceleration due to gravity. Which is always 9.81 m/s^2. People with larger masses have a greater potential energy due to gravity if they are at the same height as someone with a smaller mass. However, it is harder for people with larger masses to reach the same heights as people with small masses, because gravity is pulling them down more. PE=(1/2)kx^2 The potential energy stored in a spring: "x" is how much the spring stretches, and "k" is the spring constant. Hooke's law goes along with this: F=kx. The force of the spring is the constant multiplied by the change in the spring length. This demonstrates Newton's third law; every action has an equal and opposite reaction. When the springs are stretched by the person, they have to compress again, making the person jump higher as the trampoline returns to its original position. Because of gravity, larger masses allow the spring to be stretched out more. This can be shown by the equation F=ma, which is Newton's second law of motion. "F" is the force of gravity, "m" is mass, and "a" here is also g, acceleration due to gravity. So when mass increases, so does the force of gravity. This means the object/person is being pulled down harder by gravity. This stretches the springs of the trampoline more, creating a higher spring potential energy. But the mass is usually too heavy for the spring to move you if you just stand there, which is why you don't move unless you start jumping first. Smaller kids usually jump higher than adults, even though they have a lower potential energy due to gravity, because the trampoline can more easily spring them back up, since they are being pulled down by gravity slightly less. This is all a great example of Newton's first law: objects in motion will keep moving, and objects at rest will not move, until acted upon by an outside force. The outside forces that keep you on the trampoline are both gravity, which keeps you down, and the trampoline itself, which keeps you up. You also wont move until you begin jumping. Pushing your feet down makes you go up. (Newton's third law!)
12. ## Can you really swing over the bar?

I never realized that the reason you cant do a full circle on a normal swing has so much to do with the loose chains. Now it makes soo much more sense
13. ## The Physics of Drawing- Light Waves and Colors

Drawing is much more complicated than many people think. It also has a lot to do with physics. The main physics behind drawing is light waves. This is because light is a type of wave, which carries energy like all other waves. Light is essential for drawing, or any other kind of art. Light allows you to see, and more specifically, it allows you to see an object’s shape, color and the shadows on it. Being able to see all these things makes it possible to take a 3D object and put it on a piece of paper. The way light lets you to see objects and colors is by reflection. White light is where all the colors in the spectrum of visible light appear all at once. Examples of this is the sun. These pictures show each color's wavelength. Red has a long wavelength, violet has a small shorter one. All of them together are white light. Different objects reflect a specific color, or type of light because of their different wavelengths. Space is the only true black because it absorbs all light and colors because there is nothing for light to reflect off of. An example of light reflection creating colors is an apple. When you look at it, you see it as the color red. This is because red light is reflected off of the apple and into receptors in your eye, and all the other colors are absorbed into the apple. So, when you are trying to draw or paint, or whatever else, you have to look at an object and observe its light. This object reflects light and creates color. But there are also shadows. Rounded objects allow light to diffract. Light waves want to travel in straight lines, but when they run into an object, they diffract, or bend slightly around the edge. This makes your eye see the object get gradually darker until there is barely any light reaching it, on the side facing away from the light waves. This is why it’s difficult to accurately draw things unless you know how to look at the light instead of just the object itself. Looking for the light and dark spots of the object is what makes it look 3D on paper. I have always wondered why it seems so hard to draw, but now I know its because I’ve just been looking at the shapes instead of paying more attention to the light on it. I’ll have to keep that in mind.
14. ## Kushel.

the universe is pretty coool.
15. ## Um... Hello?

i don't think anyone knows what to expect... haha
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