CHAPTER 12 NOTES
Energy: the ability to do work.
Work: what you are doing.
You need energy to do work. With no energy, work cannot be done. Imagine when you are tired. It is very difficult to do work whether it is physical or mental. In order to gain some energy you need to eat something healthy or get some sleep. It’s like recharging your own personal battery.
Potential energy vs. kinetic energy
Potential energy is energy stored based on the objects mass and/or position.
Kinetic energy is energy of motion.
Mechanical energy is the total amount of energy of an object whether it is in motion or at rest. Mechanical energy can be all potential, all kinetic, or some of both.
You can increase the potential of something by changing its position or adding mass. This in turn will give the object more kinetic energy.
As an object moves its energy transfers from potential to kinetic. The potential an object starts with will never be gained again unless you add another force to it. For example on a rollercoaster. In order to get the car to its greatest potential, a motor pulls the car to the top of the biggest hill. The car will never reach the height of the first hill because its energy is being transferred to kinetic as it goes through the rest of its hills and loops. You would need to push the car or have another motor pull the car back to more potential. Some of the energy is transferred to heat due to friction, the opposing force of motion between two surfaces that are touching. In this case it is the wheels and the track. You can increase the potential of this rollercoaster by making the first hill higher or increase the mass of the car.
Law of conservation of energy: energy can be neither created nor destroyed. It can only be transferred. As it transfers, the total amount will always be the same as long as it is in a closed system (well-defined group of objects that transfers energy between one another).
All energy involves either motion or position. They types of energy are:
- Thermal: the total energy of the particles that make up an object. The energy will be more if the temperature is higher because the particles that make up the object will be moving faster. The heat given off from the movement of particles is what will be transferred to other objects. (See the Laws of Thermodynamics below for more information on heat transfer)
- Chemical: energy of a compound that changes as its atoms are rearranged to form new compounds. This is a form of potential energy. If you have more atoms bonded together, the amount of chemical energy will be more. Examples: food, batteries, plants undergoing photosynthesis.
- Electrical: energy of moving electrons.
- Sound: an object’s vibrations cause air particles to vibrate .
- Light: vibrations of electrically charge particles. Air particles do not vibrate with light energy. Light energy can travel through a vacuum.
- Nuclear: energy associated with changes in the nucleus of an atom. This can occur during fusion (two nuclei fuse or join together) or during fission (one nucleus splits apart). Examples: The sun uses nuclear fusion in the core to give off its energy and nuclear power plants use nuclear fission with uranium to create large amounts of energy.
Energy transfers from one form to the other. When there is a transfer, the amount of energy should remain the same or close to the same. Whenever there is energy, some is always transferred to heat which is never gained back.
Laws of Thermodynamics (flow of heat)
Zeroth Law: If two things have the same temperature (thermal equilibrium), no heat will flow between them.
First Law: Energy is always conserved (always adds up) throughout the universe.
Second Law: Whenever we use energy, some of it becomes heat.
This law has taken away the dreams of many who believed that there could be a perpetual motion machine. This is a machine that would put out exactly as much energy as it takes in. So it would always move. But, because some is transferred to thermal energy it will always need more. Bummer!
Third Law: At absolute zero, all motion stops, but we can never quite get there. (look on page 392 in your book)
Energy conversions are a change from one form of energy to another.
Think about the pendulum we hung from the ceiling. If I raised the ball higher, I gave it more potential. As I released the ball, the pendulum swung away from me changed into kinetic energy. When it reached its highest peak again it went back to potential. This continued until the transfer slowed down the pendulum because some of the energy transferred heat to the air particles around it and to the string holding the ball.
Green plants use chlorophyll and light energy from the sun to produce the chemical energy in the food you eat. This energy is then transferred into kinetic energy when we do work and also thermal energy in order to maintain our body temperature.
An alarm clock uses electrical energy to change into light and sound energy.
A battery uses chemical energy to change into electrical energy.
A light bulb uses electrical energy to change into light and thermal energy.
A blender uses electrical energy to change into kinetic energy and sound energy.
ENERGY RESOURCES:
- a natural resource that can be converted by humans into other forms of energy in order to do useful work.
We are constantly trying to find other sources in order to replace those we run out of.
Nonerenewable resources cannot be replaced after they are used or can be replaces only over thousands or millions of years.
Example: Fossil fuels, energy resources that formed from the buried remains of plants an animals that lived millions of years ago. These are coal, petroleum, and natural gas.
Most of our coal use is for electrical power. Petroleum is mostly used for gasoline, kerosene, and wax. Natural gas is used in our homes for the stove and heating systems.
Nuclear energy is considered a use of nonrenewable resources because our supply of uranium is limited.
Renewable resources can be used and replaced in nature over a relatively short period of time. We use solar energy for power, energy from water, energy from wind, energy from within the Earth’s crust, and from plants or other organic matter called biomass.
All types of resources have their good and bad. Look on page 351 for more information.
