Unit 5 Blog Post

Unit 5 was a pretty equation heavy rather than conceptual. We first began by going over work. Work is force x distance, but the force and distance both have to be parallel or no work is being done, and the only distance used is vertical. We introduced work with a experiment in which we walked, and ran upstairs. The point of this exercise was to understand that no matter how fast you reach a fixed height you will be doing the same amount of work because work is simply force times distance. But when you added weights you changed the work because you changed the force you had to carry in that upward distance. In this experiment we were not just introduced to work but also power. Power is work over time. Meaning when we ran up the stairs we had different power than from when we walked. We actually had more power when we ran, this is because the time was less and when you divide the work over a smaller time you will have a larger result than a larger time. Power is measured in watts. Hmmm... Watts and Power? Sounds familiar. Oh yeah that is because when we hear power we think of horsepower. Horsepower is what they rate an engines strength and speed on. A single horsepower is 746 watts and when running up the stairs I was able to produce a full horsepower.
     Our next topic was Kinetic energy (KE) and it's relationship to work and Potential energy (PE). Kinetic energy is the energy and object has while in motion. Or work in motion. KE= 1/2mv^2. KE and work are related in that change in KE(or delta KE) = work. My podcast group chose this topic and here is our video for it...

Our video showed Luke's car changing velocities and therefore kinetic energies and their respective differences and then we found the distance it would require to stop by using the equation Change in KE= work. Because the velocity is the KE equation is squared the stopping distance will be squared. say you have a velocity of 2, your stopping distance would be 4, 3 would be 9 and so on. We used the stopping distance as our bread and butter in explaining the relationship between Kinetic Energy and Work. Potential energy is the energy that depends on an objects height. PE=mgh. An object will have high PE at a large height and zero PE on the ground. Another group in our class did a video on PE relationship with KE. 

They use a pendulum to describe the relationship between potential and kinetic energy. PE and KE are always conserved. The max energy will always be the su of KE and PE. A resting object at its peak will always have it's highest PE and lowest KE (0). At the bottom it will have its highest KE and lowest PE (0) and will reverse when it gets back to the peak.
    The last key concept we learned was machines. Machines help us by directing the work we do on an object more efficiently. To carry a 1N box 1m up we can't change the work done, but we can decrease the amount of force we put in. We can do this because work=f x d, and we can change the distance it takes us for us to get to the target distance. We can do this because if we are trying to get a box 1m high the only thing important to work is the force and upwards distance, but we can increase the horizontal distance up toward the vertical height we want to reach and fraction the force we exert. Ramps, Pulleys and levers are machines that do such things. By increasing the D in we are able to decrease the f in. This is how machines help us, not by decreasing work, but by making more efficient use of our force put in.

unit 4 blog post

I think unit 4 was my favorite physics lesson so far. Every lesson in physics is applicable to real life but I felt as this unit hit my areas of interest. We kicked of the unit by first going over torque. Torque at a mathematical level is force x lever arm. But scientifically torque is the tendency to rotate at an objects axis of rotation. You can increase torque on objects to help you achieve tasks as well. This video gives examples on how to... 

In class we had a mass of meter stick challenge in where we were assigned a meter stick with a 1 kg weight attached to it. To find the weight we had to find the center of mass of the meter stick without the weight attached. We accomplished this task by finding the torque on both sides of the meter stick while balancing it with the weight attached. 

All objects have a center of gravity/mass. We can manipulate the distribution of our mass to keep our center of gravity from rotating. In football linemen crouch with their legs far apart and knees bent. They do this and it makes them harder to rotate or be knocked over for two reasons. Spreading ones legs widens their base of support which gives more space for their weight to go over. An object looses balance when it's weight is not over its base of support. The bent knees keep a person's weight close to their axis of rotation and this keeps them closer to the ground and base of support which makes falling over more difficult. This video explains the application...

Objects rotating  have two velocities, tangential and rotational. Tangential velocity is the distance cover in a spin while rotational is the amount of spins over given time. We see these in gears. You can have tow gears connected, a small and large, and they will both have the same tangential speed but different rotational velocities. This is because they both spin the same amount of notches per second but the smaller gear finishes a rotation quicker. Th wheels of train tracks are tapered so they have varying rotational velocities and because the train spins on wheels, it is the rotational velocity that controls the speed and direction of the train.
     We also learned about rotational inertia. As an object spins, the distribution of it's mass can change it's rotational inertia. When an objects mass is closer to it's axis of rotation it has less rotational inertia and spins faster. This is how ice skaters are able to control the rate at which they rotate. My group video explains how rotational inertia works and how it is conserved.

The last thing we went over was centripetal force which literally means center seeking. This force is by the moon stays revolving around earth. Earths gravity acts as a rope pulling the moon toward it so the moon does crash off somewhere. Say you have a bucket of water and rope attached plate. You put the water on the plate and start to spin it around your head. The water does not spill because the centripetal force keeps it towards the middle of the cup.