Nov. 3. 2010

Hey,

So today in class we started with the Transparency 11-3 Worksheet. (the one about Potential Energy and Kinetic Energy)

answers:

1. What type of energy exists in the situation shown?
- Gravitational Potential Energy/ Kinetic Energy

2. How are these two types of energy defined?
-GPE: energy stored in a system as a result of the force of gravity between the object and Earth; Ep=mgh
-Ek: energy of motion; Ek=1/2mv^2

3. At what points is the kinetic energy of the ball at a maximum?
-Just as the ball is thrown up and when it returns to its lowest point, velocity is the greatest at these 2 points.

4. When is gravitational potential energy at a maximum?
-At the top of its trajectory; Gravitational Energy is proportional to the height of an object above Earth's surface

5. As the gravitaional potential energy increases, how does the kinetic energy change? Is this an example of an open or a closed system?
-Kinetic Energy decreases; closed system

6. How does the sum of the kinetic and gravitational potential energy change? What Principle does this demonstrate?
- Sum stays constant; Law of conservation of Energy

7. How many times during one rise and fall of the ball are the gravitaional potential and kinetic energy equal?
-twice


Next we moved onto the last part of the unit; Force and the Spring

One of the first things we need to use when working with springs is its deformation i.e. how much it stretches from its normal length when a force is added. This will be shown with X

This means that a graph of Force x X will be a straight line
http://www.pa.msu.edu/courses/1998spring/ISP209/homework/hmwk3/Hw03gr.gif

The slope of the graph, (K) can be calculated by k=rise/run=F/X

"K" is a constant called the spring constant and has the dimensions of force per unit length (N/m). "K" is also referred to as the stiffness because the larger the value for "k" the stiffer the spring

It is important to understand that, in the equation F=kx, the Force is coming from something else added to the spring. This means that when the spring is compressed, both X and F are negative (-). When the spring is stretched, bothe are positive (+)

This is explained in Hooke's Law ffor a spring: "The force applied to an ideal spring is given by F=kx where k is the spring constant and x is the displacement of the spring from its unstrained length"
................ for a diagram of the above, click on the link below
http://www.pa.msu.edu/courses/1998spring/ISP209/homework/hmwk3/Hw03gr.gif

Derivations for F=kx

W= area of triangle
W=1/2 Fx
W=1/2 (kx) (x)
=1/2 kx^2

Es=1/2kx^2


We also worked on a lab based on what we just learned, in which we put weights on a spring and measured the displacement and Force exerted. The lab is due tomorrow

If you have any questions, feel free to ask Mrs. Kozoriz

HAVE A GOOD EVENING!!!