This class is boss,yo

[obviousphysics-blog]

Simple Machines

Simple machines are meant to give mechanical advantage when it comes to doing work. An example of a simple machine is an inclined plane. By forcing you to exert the force over a longer distance, less force is needed to move an object up an inclined plane than a vertical incline. Another good example of an inclined plane is a lever, such as one's arm. A lever allow a lot of force to be exerted over a short distance at one end of the lever, while at the other end, a small force works over a large distance. 

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This week we began talking about machines. A machine is a device for increasing a force or changing the direction of a force. Fd(input)=Fd(output). This equation shows the that the work input is the same as the work output. With this you can also calculate the efficiency of a machine. Wout/Win *100. There are 3 common simple machines, the lever, the pulley, and the incline. No machine has 100% efficiency.

[obviousphysics-blog]

I think it's especially interesting that the different parts of your body are simple machines as well. Take, for example, your arm, which works a lot like a lever. 

[obviousphysics-blog]

Christmas Trees

Today, my dog Max partook in his holiday tradition of trying to rip the Christmas tree down. His stunt made me think of potential and kinetic energy. While the tree was just sitting there, it had only potential energy. As soon as Max began pulling it down, that potential energy converted into kinetic energy. Finally, when the tree reached the ground, it had no potential energy. This year, like always and probably by some Christmas miracle, Max's attempt to sabotage Christmas resulted in absolutely zero ornaments on the tree being harmed. 

[obviousphysics-blog]

Mechanical advantage

I've already talked a little about pulleys, but we actually got to use them in a lab on Monday. What we found was the difference between actual and ideal mechanical advantage. Actual was equal to resistance force over actual effort force, while ideal was effort distance over resistance distance. Actual advantage takes into account friction so it's lower than ideal, and will never have 100% efficiency, as no machine can be perfectly efficient.

[canyoubelievethisurlwasavai-blog]

A pendulum displays how kinetic and potential energy very well. We can see how at the bottom there’s more kinetic energy than potential energy. Then more potential energy than kinetic energy at the sides.

[obviousphysics-blog]

Of course, no matter where the pendulum is, energy is conserved. It's just in different forms. 

[obviousphysics-blog]

Rubber bands are a pretty good example of potential energy in action. When you pull a rubber band back, and hold it that way, all of the energy is held in place, waiting to be used. As soon as you take your finger away and the rubber band springs into action, all of that potential energy is converted into kinetic energy. 

[obviousphysics-blog]

Pulleys

I think it's worth examining how pulleys affect the amount of energy needed. Since work is equal to force times distance, a great force over a short distance can produce the same work as a small force over a great distance. Consequently, pulleys increase the distance over which a force is applied. This means that a smaller force is needed to do the same amount of work. 

[obviousphysics-blog]

Energy

Today in class, we learned how position affects energy. For example, at the top of a hill, a roller coaster cart might have 1000 joules of potential energy. At the bottom of that hill, it would have zero potential energy. However, energy is always conserved, just in a different form. That cart at the bottom of the hill might have zero potential energy, but it has 1000 joules of kinetic energy. The cart at the top of the hill has no kinetic energy, because it's sitting still. Total energy is just kinetic plus potential, making the two carts equal in terms of energy. 

[canyoubelievethisurlwasavai-blog]

A bow makes a good example for a lot of things in physics. The bowman does work when he pulls back on the string. Before the release, there’s a lot of potential energy being stored. This all becomes kinetic energy when the bow is released.

[obviousphysics-blog]

Momentum sort of comes into play here too. The arrow has forward momentum, while the bow has negative momentum from the string being pulled back. Together, they equal zero. 

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Our Lab and Power

Our lab for this cycle centered around power. We all dashed up the steps outside Parents' Hall, timed each other, and calculated horsepower based on the distance of the steps, weight, and time. Ultimately, all of the data we found seemed to support what we had been taught in class about power. Power is a function of work over time. The heavier someone was, the more work they put out, and subsequently they produced more power. However, time came into play as well. The slower someone moved up the steps, the less power they produced. Those with the most power generated had both larger weights and faster times. 

[obviousphysics-blog]

Trampolines

I think trampolines are a pretty good example of kinetic and potential energy in action. When you jump up, you have kinetic energy, from your motion. But when you fall back down to the trampoline and hit its surface, you cause it to dent down. While you're in this sort of ditch in the trampoline, you have a great deal of potential energy. When the trampoline eventually springs back to a flat state, you're propelled into the air, and all that potential energy becomes kinetic. 

[obviousphysics-blog]

Work

One of the topics we discussed this week was work. Work is equal to force times distance. Work, scientifically, requires motion. This is because force is required, meaning motion must be present as well. Work made me think of mowing a lawn. The further you push it, the more work you do. The more force you push the lawnmower with, the more work is done.

[obviousphysics-blog]

Transfer of Momentum

I went bowling a few weeks back, and I think it actually has a good deal to do with momentum. The pins at the end of the lane have zero momentum, since they're sitting still. The bowling ball has its own momentum, from its mass and velocity. When it hits the pin, due to elastic collisions, the bowling balls and pin both move forward with the same total momentum. However, if the mass of the pins and the ball were the same, all of the bowling ball's momentum would be transferred to the pin. 

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Impulse and car accidents

I've written about this before, but impulse is basically just the change in momentum. You calculate by multiplying the force and difference in time. The reason bumpers on cars are made to crush in is so that the force from the other car hits your car over a greater period of time. This makes the change in momentum less sudden, and therefore less dangerous. This same principle is applicable to the airbags in your car, increasing the amount of time over which the force is applied to you. 

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Conservation of momentum

One of the topics we focused on this week was the conservation of momentum. Basically, this means that the momentum of two objects that have collided is equal and in opposite directions. The formula for this is m1v1+m2v2=m1v1'+m2v2', or that the added masses of the objects times their velocities is equal to the added masses of the objects times their new velocities. This made me think two people colliding. The momentum with which they each fall back after the collision is equal for both people. However, the directions are opposite. 

[obviousphysics-blog]

‘Puppy Day’ shakes off the stress at GMU law school : http://wapo.st/vPgEOG

We should get some puppies for the upcoming test Mr. Love.

[obviousphysics-blog]

Impulse

In class, we've just begun to explore impulse. Impulse is the relationship between a force and how long it is in contact with an object. Impulse is found by multiplying the time interval and force. For example, a 50 Newton force applied to an object for a time interval of 1 second would create the same impulse as a 1 newton force with a time interval of 50 seconds. Think of trying to tackle someone. If you tackle them with great force, it might not take long at all to overcome them. On the other hand, using a lesser force when tackling them might require you be in contact with them for a greater amount of time.