# reedelena

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1. ## Electric Fields

Positive charges their electric fields are pointed out away from the charge. A negative charge their electric field is pointed toward the charge. When a positive and a negative charge are brought close together they will be drawn toward each other, they are magnetic. The electric fields never cross each other when they are magnetic. When you bring a magnetic positive charge and a positive charge together they will be repulsive, the same holds true if you bring a negative charge and a negative charge together. They are repulsive charges. The equation for electric field strength is E=Fe/q.
2. ## Electric Current

In physics we learned about electric current, resistance and conductivity. Electric current is the flow of positive electric charge and the units are amperes (A) which is equal to one coulomb per second. To find the electric current you divide coulombs by the time. An example to find the electric current is when you are given 3000 coulombs and .2 seconds. Divide 3000 by .2 and you would get 15000 amperes. Conductivity is how well a material conveys electric charge. Conductivity depends on the number of free electric charges available to move and also the mobility of charges. Resistivity is how well something impedes the electric charge.
3. ## wave interference

Interference is when two waves are coming towards each other and you want to determine what happens when the two waves meet. Interference occurs when waves in the same medium, meet at the same time, and at the same location. Superposition is when you add the two waves together to find out what happens to the amplitude at the point that they meet. A constructive interference is when the amplitude is higher (bigger) then the two initial waves. The destructive wave is when you add the two amplitudes the number should be smaller then the two initial waves. With a destructive wave there is a point where the two waves actually make a straight line. You still add the two amplitudes but the resulting number is smaller. With constructive and destructive waves after the waves have meet they continue on in the direction that they were initially going in. The last type of interference is a standing wave, that is when two waves are approaching in the same medium, same frequency, same amplitude, and traveling in opposite directions.
4. ## Wave Equation

Like for everything else in physics there is an equation for waves. The equation is velocity= frequency times the wavelength. Velocity is determined by the medium (speed), which means that the medium determines how fast or slow the wave is. If frequency increases wavelength decreases, they have an inverse relationship. Meaning that if one goes up the other one goes down. Frequency is measured in hertz, velocity is measured in meters per second, and wavelength is measured in meters. If you were given a problem where it says that the frequency of a wave is 10 hertz and the wavelength was 2 meters, to find the speed you would multiply the frequency and wavelength together resulting in 20 meters per second. If you were asked to find the frequency of a wave and you were given the velocity and wavelength you would divide velocity and wavelength.
5. ## Waves

Lately in physics we have been talking about waves and the different types of waves. We learned about a transverse wave which are perpendicular to the direction of wave travel. Besides transverse waves we learned about a longitudinal wave which are parallel to the direction of wave travel. Another type of wave is a mechanical wave, for a mechanical wave to work it must have a medium. Sound is a type of mechanical waves they need a medium for them to work. Which is why in space you can not hear sound because there are no mediums for the sound wave to travel though. When a wave enters a new medium its frequency stays the same. The last type of wave is an electromagnetic wave, and it is different from a mechanical wave because it does not need a medium to travel through. A single vibratory disturbance in a wave is called a pulse. The amplitude is the height of from when the wave is at rest to the crest.
6. ## Springs

The force of a spring, the more you stretch or compress a spring the greater the force of the spring. Hooke's law tells us the force of a spring is equal to -kx. The K is the spring constant, the stiffness of the spring and the x is the displacement from equilibrium. We also learned what elastic potential energy is, which is the work done in stretching or compressing the spring. The equation of elastic potential energy is (1/2)kx^2. A spring with a spring constant of 4N/m is compressed by a force of 1.2 N. What is the total elastic potential energy stored in the compressed spring? We first have to find the displacement of the spring. We rearrange the force of a spring formula so that x=Fs/-k. We divide 1.2 N by -4 N/m and we get -.3m. Then we take our x and we plug it into the equation (1/2)(4 N/m)(-.3m)^2 and we get .18 J.
7. ## Ice Skating

We have been talking about the winter Olympics in physics the last few days and when I think of the Olympics the first thought that pops into my brain is brrr that's cold. The next thought is how I always admire the ice skaters and how they are able to turn so quickly in a certain amount of time. One of the units that we have learned in class is frequency, which is the number of revolutions completed in one second. When you watch a professional ice skater you think that they are doing one revolution in one second, when in reality they are doing three revolutions in one second. To find their frequency when turning we would divide the number of revolutions they have done by how long their sequence is. They also apply angular momentum which characterizes an object's resistance to change in rotation. When they are rotating they apply a force called a torque it helps speed things up.
8. ## Science of Superman

In class Ms. Winchester showed us a scene from The Big Bang Theory and it talked about how Superman and many comic books are full of scientific errors. First of all men can not really fly, so that defies everything we have learned about gravity. However if men did fly they would not be able to catch a women falling out of a building without initially killing them. Say that a women is falling out of a building and she is accelerating at a certain amount and superman is flying even faster so that he is able to catch her his acceleration is greater. So if he was to have his arms (which are made of steel) out in front of him to catch her she would be cut into three separate piece. So she would have died either way, either in the arms of Superman or by hitting the pavement.
9. ## Skiing

Tis the season to be skiing, even though I hate winter and i do not ski myself physics is applied when you ski. When you look at skiing you can apply Newton's three laws the first law being an object in motion will stay in motion and object at rest will stay at rest until acted upon by an outside force. This is how a skier is able to go downhill without stopping, the gravity is what puts the skier in motion and the skier will not stop until an outside force acts upon it. That outside force could be another skier, a bump on the hill, or a tree that just happens to be there. Newton's second law states that force equals mass x acceleration. Using this we can calculation how much force we have or going to have when we go down a hill by taking our mass and multiplying it by our acceleration. By using this we can calculate our force we can also figure out how much it would hurt if we were to hit a tree. And our last law states that for every action there is an equal and opposite reaction. This is used when we are using our poles to push the ground away from us to get started, in a sense the ground is pushing back.
10. ## Power

In class we have been talking about power and how to calculate the power. Power is the rate at which work is done, the same amount of work can be done with different supplied if the time is different. If an 8 kg box is raised to a height of 2 meters in .5 seconds, what amount of power was supplied. To find the power we have to use to formula that we used in class which is work over time. To find work we must multiply the force times the displacement. We would multiply 8 kg, 9.81 m/s^2 and 2 meters to find the work. Our work in this problem is equal to 156.96 Joules. Then we would divide our work by the time that is provided for us .5 seconds. Once you have divided Joules/second you would get the answer 313.92 watts. This tells us the rate at which the work is done.
11. ## Weight lifting

In the last few week of physics we have been talking about work and energy and when it is applied. Work is the process of moving an object by applying a force, so if we are pushing someone and they end up falling in that direction then you are applying work to them. When I think of work and applying a force I think of a weight lifter and how much force they have to apply to the weights to be able to life them. If a weight lifter is lifting a 100 kg weight and their displacement is 2 meters the work being done is 1962 Joules. For a force to have done work on an object it must have caused a displacement, the weights had originally been on the ground and were raised two meters. Weight lifters use a lot of work and energy to be able to lift their weights.

13. ## Physics when you swim

I like how you applied physics to swimming, it sounds like a very interesting sport. I like how you applied initial and final velocity in your example.
14. ## The physics of dancing

Just like in every other sport, you can apply physics to dancing. When we are jumping off the floor for a certain jump we are a.) using newton's third law b.) we are also using acceleration. To get ourselves off the ground we have to push off the floor, when we push down onto the floor the floor pushes back on us allowing us to leave the floor. When we are preparing to jump into the ground we have to run, we are applying acceleration to our bodies so that we are able to defy gravity's acceleration of 9.81 m/s^2. We can also apply Newton's first law to dancing, an object in motion stays in motion unless acted upon an outside force. when we perform certain turn sequences, which is when we continuously turn in circles, we have to have an outside force (a fellow dancer) stop us because our force is so great that we are not able to stop ourselves.
15. ## Every force has an opposite equal force

Newton's third law is for every force there is an equal opposite force and this law can be applied to many different sports, especially swimming. As a swimmer you have to go from one end of the pool to the other end of the pool multiple times and the way we get there is by applying Newton's third law. When we are swimming freestyle to go forward we place our hands in in front of us, however we are not pushing the water forward, we are pushing it behind us. When we push the water behind us that is how we propel ourselves forward. When we are flip turning off the wall we are pushing down on the wall and the wall pushes back on us and that makes us leave the wall. The last way that it is applied is when we are diving off the blocks, we push back on the block and it pushes back on us which enables us to go forward off the block. That is how Newton's third law is applied to swimming.