weeerk - unit 8

Until now, we have been learning about work, or any change in energy. Today we learned about power, and how that is the result of work divided by time. The units are joules/sec, also known as a watt. During our laboratory, we learned that objects that are more massive take more power to move. This is because the rate at which work is being done is greater than the rate of an object that is less massive. The difference between work and power, is that work is the amount of energy an object uses, and power is the rate of the energy being used.

The cost of electricity is about 20c/ Kwh, the following equation is the cost of one light bulb left on for ten hours straight.

0.21 Kw * 10 hrs * 0.20 c/Kw hr = $0.42

potentiality - Unit 8

To blow off steam from a tough day of physics, I went to go work out at my gym after school. During my speed bag lesson, I noticed that there was a pendulum right before my eyes! The speed bag located on a hook (to allow the bag go back and forth) was actually a pendulum! This unit was about work and to understand it, a pendulum was used to show how work is neither created nor destroyed. Where the pendulum lays when no one has touched it, is the equilibrium point. We can call this 0m, and nowhere on the pendulum no matter how it is pushed can go past the equilibrium point. When the weight of the pendulum is brought up above the ground at a certain point and released, the weight should go back and forth and never go higher than the dropping point. When the weight of the pendulum is suspended in the air, it has potential energy, because there is distance for the force of the ball to come down. Because it isn't at its equilibrium point, it has more than 0 potential energy. When the weight is released, the potential energy decreases as the kinetic energy increases (an inverse relationship). When the pendulum is swinging back and force, the equilibrium point is when it'd be going the fastest because there is no force working against it/for it. If you had the same situation (suspending a pendulum above the ground) but pushed the weight of the pendulum forward, no longer will it return to the same spot. It will go back and forth faster, and end up higher than the dropping point. In this video of me speed bag boxing, I am putting energy into the pendulum to make it go back and forth. Because I hit it with a great amount of energy (and the weight is very light) the bag goes back and forth quickly, and hits either side of the top of the pendulum.

the smell of success should NOT be the smell of eggs! - Unit 7

For this project, I was assigned to my partner Nalei. When we came up with an egg catcher, we agreed that in order for there to be less force on the egg (so it won't break), we had to somehow increase the contact time, and decrease the the impulse.

What we did: We used a plastic container and cushioned the bottom and sides with shredded newspaper. There are about ten sheets of newspaper on the bottom of the container, so there is something between the hard plastic and the shredded newspaper. Towards the middle of the container, there is a cup of cotton balls surrounding the egg. The egg is wrapped in one sheet of newspaper, and is sitting on the cotton balls. On top of the wrapped eggs, there are more cotton balls and newspaper.

What we used:
1 plastic container 23 cm in height, 13 cm in width, 17 cm in length.
20-30 cotton balls
15 sheets of newspaper

Why we did: The four inches of newspaper were supposed to cushion the eggs landing, and create a separation between the egg and the plastic. The cotton was supposed to increase the contact time, as well as create more of a cushion. Wrapping the egg in newspaper was supposed to protect the egg more.
...success?

No, I failed. A lot of the mass came from the lid of the plastic container, which we weren't expecting to land on the bottom. The lid split open, and the egg couldn't handle all of the force.

delta P - Unit 7

In this unit, we learned about momentum. In order to find momentum, you must know the mass and velocity. To find the change in momentum, you will have to know the average force and change in time. To be put simply, momentum is just inertia in motion. When we look at momentum between two objects, some things never change. If the two colliding objects have different masses, they will still have the same force of impact, the impulses would be the same, the changes in momentum would be the same (same thing as impulse, changes in momentum and impulse are two interchangeable words), however, the speeds of the two objects will be different (because mass is inversely related to velocity).

Here is a sample problem: A 50kg man is running with a velocity of 10m/s north onto a 1000 kg car. When the man is in the car, the velocity is 15 m/s north. What was the velocity of the car after the man jumped on it?

Equation: MboyiVboyi + McariVcari = (Mboy + Mcar) Vf

50kg(10m/s) + 1000kg(15m/s) = (50kg+1000kg) Vf

500 + 15000 = 1050Vf

15500 = 1050vf

Vf = 14.76 m/s

all work, no play - Unit 7

After our long three day weekend, we got right back into physics by learning the kinematics of collisions. In this picture that mysteriously looks very similar to the one Mr. Blake took, our class is having a water balloon contest. This is to prove that objects have a limit to how much force they can stand. Like someone falling off of a 20 story building, "It's not the fall that kills them, it's the landing surface." What this quote is saying, is that when you are falling, your body increases velocity and the final force you land with is so great that your body can't handle it; therefore you die. Well in this fun activity we did at the end of class, we had to catch the water balloon in such a way that would cushion the water balloon so it wouldn't burst. We learned that if we increase the time where the balloon was caught, the less force would impact the egg. In the equation: delta P/change in time = avg. force, we see that force and time are inversely related, indicating that the more time it takes to catch, the less force will be exerted on that object.

I learned many concepts in this class that I wouldn't have learned in any other class. Most of everything I learned is on other blog posts.
Physics is enjoyable for me because I am finally learning the "behind the scenes" of what's going on when objects are in motion. Many questions I had about why something happens have been answered by taking this class. For example, I always wondered why a ball would still bounce up and down in your hand when you were in a car. Why wouldn't it go flying straight through the back window? I am glad I took this class over the summer. I am also really glad I have friends who I can enjoy this difficult class with. I can rely on them for help, and they make it fun. Four to six hours everyday seem like nothing!
In physics, the concepts were really hard for me to understand the first time around. Since this class is so compressed, we had to learn everything really quickly. The ideas and concepts kept getting harder and harder. This is an ongoing challenge for me, but I've fixed the problem by asking Mr. Blake and Colin for help, asking my wunnerful table mates and going to extra help after school. Because I don't understand everything as well, I need to spend more time on homework.