1. Chapter 4
Section 2

2. Changing Forms
Going back to the money analogy, how do you change the form of money?
Just like with money doing certain activities can change the from of energy.
You may start off with electricity, but once you turn on a light the electricity changes to light energy and heat energy.

3. When you have PE it can always be converted to KE.
Look at the picture below, as the ball reaches it its peaks it has mostly PE, but as it moves the PE gets transformed into KE. It has the most KE at its lowest point.

4. Projectile’s such a throwing a ball work similarly.
As the ball starts out it has mostly PE. When it reaches it’s peak and begins to descend it is mostly KE. When it reaches the ground it again is PE.

5. Mechanical Energy
In order to convert PE to KE or KE to PE you must first know how much total energy is in the system.
Mechanical Energy (ME) is the total amount of energy in a system.
To find ME you add the PE and the KE together.
ME=KE+PE

6. ME Practice Problems
If a ball in motion has a kinetic energy of 12 J and when at rest has a potential energy of 8 J what is the ME of the ball?
What is the mechanical energy of a 500 kg rollercoaster car moving with a velocity of 3m/s at the top of a hill that is 30 m high?

7. Given that the mechanical energy of a paper airplane is 3. 948 J
Given that the mechanical energy of a paper airplane is J. What is the speed of the paper airplane , if its weight is 0.05 kg and is thrown from a height of 8m?

8. Conservation of Energy
Is energy always conserved?
What about when you start an action such as swinging, if you don’t continue to pump your legs what happens?
This is the effect of friction. The rope or chain rubs against itself and the person on the swing. This in turn transforms some of energy into heat and even sound. Every time a cycle is made some more energy is converted. Even the air around the person takes on some of the energy.

9. Food and Energy
Your body uses energy to allow you to be active and perform metabolic processes such as breathing, heart rate, and digestion.
This energy comes from food. The energy that comes from food is measured with calories.
1 Calorie = 4,184 J

10. Questions What is the term for energy that comes from food?
What is Mechanical Energy?
What is Potential Energy?
How does fiction affect energy?