Work, Energy, Heat Chapter 3/4 Study Guide PHYS 101
1. Mechanical energy is the energy possessed by an object due to its motion or its stored energy of position. Mechanical energy can be either kinetic (energy of motion) or potential (energy of position). An object that possesses mechanical energy is able to do work. Mechanical energy is the form involved in the operation of simple machines.
2. Objects that have potential energy do not use their energy until they move. That is why it is called "potential" energy. Potential means that something is capable of becoming active. Any object that can move to a lower place has the potential to do work on the way down, such as a marble rolling down a driveway. Objects also store energy in motion. A moving mass can certainly exert forces, as you would quickly observe if someone ran into you during a basketball game. Energy of motion is called kinetic energy. Energy appears in different forms, such as motion and heat. Energy can travel in different forms, such as light, sound or electricity. The workings of the universe plus all of present day technology can be viewed from the perspective of energy flowing from one place to another and changing back and forth from one form to another.
3. Energy can be transferred from one system to another (or from a system to its environment) in different ways: 1) thermally, when a warmer object is in contact with a cooler one; 2) mechanically, when two objects push or pull on each other over a distance; 3) electrically, when an electrical source such as a battery or generator is connected in a complete circuit to an electrical device; or 4) by electromagnetic waves. Energy is one of the fundamental building blocks of our universe. Energy can change from one form to another, although in the process some energy is always converted to heat. Some systems transform energy with less loss of heat than others. Electrical energy can be produced from a variety of energy sources and can be transformed into almost any other form of energy. Batteries store energy and transfer energy to components in a circuit. In the battery the energy comes from chemical reactions. Electricity is important because we can use it to make so many things work (electrical energy). For example, a bulb converts electrical energy into light energy and a speaker converts it into sound energy. The electrical energy generated by windmills, waterfalls and power plants is actually a secondary source of energy. To produce electricity, a heat source is needed to create the conditions in which electrical currents form. In effect, the primary source of electrical energy is the heat generated by burning fossil fuels, water power and wind power. A natural form of electrical energy can be seen in the lightning that appears during storms. Solar energy, water and wind power are sources of green energy—meaning they do not pollute the environment. Note: It is not necessary to investigate nuclear energy.
4. A machine is a device that makes work easier by changing the size or direction of a force. When you use a machine, you do the work on the machine, and the machine does the work on something else. Mechanical advantage is the number of times the machine multiplies force. Ideal Mechanical Advantage (IMA) is what is desired of a machine, where Actual Mechanical Advantage (AMA) is what the machine actually does. A lever is a simple machine that has a bar that pivots at a fixed point called a fulcrum. A pulley is a simple machine that consists of a wheel over which a rope, chain, or wire passes. A simple machine that consists of two circular objects of different sizes is known as a wheel and axle. The mechanical advantage of a wheel and axle is the radius of the wheel divided by the radius of the axle. A simple machine that is a straight, slanted surface, and facilitates the raising of loads is an inclined plane. A compound machine consists of two or more simple machines put together. In fact, most machines are compound machines. Some examples are a pair of scissors and a bicycle.