Mechanical energy is the sum of kinetic and potential energy in a mechanical system, often simplified for high school physics. The total mechanical energy can be calculated by adding the potential and kinetic energy of the system. Mechanical energy is different from chemical and nuclear energy and can be converted into other types of energy.
Mechanical energy is the sum of the energy in a mechanical system, or any group of objects that interact according to basic mechanical principles. This includes both kinetic energy, the energy of motion, and potential energy, the stored energy of position. Typically, in a mechanical system, gravity is the only large external force that needs to be considered. In a chemical system, on the other hand, all forces between individual molecules and atoms must be taken into account.
Background generale
Mechanical energy exists as both kinetic and potential energy in a system. Kinetic energy is present whenever an object is in motion. Potential energy is based on an object’s location; it is stored energy and cannot function on its own. It can, however, be converted into other forms of energy, including kinetic energy. A bowling ball suspended 10 feet (3m) above the ground, for example, has no kinetic energy because it’s not moving. However, it has a large amount of potential energy (in this case, gravitational potential energy) that would be converted into kinetic energy if the ball were dropped.
High school physics lessons often begin by instructing students in the basic principles of mechanical systems and their energy. This is because they are generally easier to visualize and simplify. Basic calculations on these systems can be done without using calculus. In most simple physics problems, the mechanical system remains closed and factors that would normally deplete the system’s energy, such as friction and air resistance, are ignored.
How to calculate mechanical energy
The total mechanical energy can be calculated simply by adding the potential and kinetic energy of the system. Potential energy (PE) is the product of the object’s height above the ground (h), its mass (m) and the gravitational acceleration of the earth (g, which is 9.8 m/s2).
PE = h × m × g
The kinetic energy of an object (KE) is the product of 1/2 its mass and its velocity squared (v).
KE = 1/2mv2
Mass is expressed in kilograms (kg), height in meters (m), velocity in meters per second (m/s), and energy in joules (j).
For example, the potential energy of a 5-kilogram (11-pound) bowling ball that is 3 meters (10 feet) above the ground is 147 joules (5 kg × 3 m × 9.8 m/s2 = 147 j) if the ball is in motion or at rest. If that ball also falls at a speed of 2 m/s, its kinetic energy is 10 joules (1/2 × 5 kg × 22 m/s = 10 j).
Once the potential and kinetic energy are known, the total mechanical energy can be found. The two types of energy are simply added together.
Mechanical energy = PE + KE
In this example, the total mechanical energy of the bowling ball is 157 joules (147 j + 10 j = 157 j).
Mechanical energy vs. chemical and nuclear
There are many other forms of energy, and it can sometimes be difficult to distinguish one from the other correctly. Chemical energy, for example, is that energy stored within the chemical bonds in molecules. Nuclear energy is the energy present in the interactions between particles in the nucleus of an atom. Mechanical energy, by contrast, generally ignores the composition of objects and looks only at the objects in question, not caring about their molecular composition.
This focus is designed to simplify calculations for mechanical energy and mechanical systems. Objects in these systems are generally treated as individual objects rather than the sum of billions of molecules. Calculating both the kinetic and potential energy of a single object is a simple task; calculating these types of energy for billions of molecules would be extremely difficult. Without simplifying the parts in a mechanical system, scientists would have to examine individual atoms and all the interactions and forces between them. This is typically reserved for particle physics.
Conversion between energy types
Mechanical energy can be converted into other types of energy using special equipment. For example, generators are designed to take mechanical work and turn it into electricity. Other types of energy can also be converted into mechanical energy; for example, a car’s internal combustion engine converts the chemical energy contained in the fuel into mechanical energy used to propel the car.
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