15.1 Energy and Its Forms

Chapter 15: Energy

15.1 Energy and Its Forms

Energy &Work are closely related:

·  Energy is the ability to do work. Energy is transferred by a force moving an object through a distance.

·  Any object that has energy has the ability to created a force.

·  Work: is a transfer of energy. When work is done on an object, energy is transferred to that object.

·  Work is done by forces. Work is done on objects.

·  Work in a physics problem means force times distance.

·  The joule is the SI unit of work & energy.

·  Energy is measured in joules, the same units as work. That is because energy is really stored work.

·  If you push a box with a force of one Newton (N) for a distance of one meter (m), you have done exactly one joule of work.

·  Energy can take many different forms and can always be measured in joules.

Kinetic & Potential Energy: 2 general types of energy.

·  Kinetic energy: the energy of motion

·  The kinetic energy of any moving object depends upon its mass & speed.

·  Kinetic energy increases as the square of the speed. This means:

o  If you go twice as fast, your energy increases by 4 times (22 = 4)

o  If your speed is three times higher, you energy is 9 times bigger. (32 = 9)

·  Kinetic energy increases with mass.

·  Double the mass = double the KE.

·  Kinetic energy increases with speed.

·  Double the speed = quadruple the KE

? Why would tripling the speed at which a car is

moving have a greater effect on its kinetic energy

than tripling its mass?

·  Potential Energy: energy that is stored, energy with the potential to do work.

·  Potential energy comes from the position of an object relative to the Earth.

·  Potential energy that depends upon an object’s height is called gravitational potential energy

o  An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity.

o  Elastic Potential Energy: the potential energy of an object that is stretched or compressed.

Forms of Energy: each of these forms of energy can be converted into other forms of energy.

·  Mechanical Energy: the energy associated with the motion and position of everyday objects is mechanical energy.

·  Thermal Energy: Heat, the particles that make up matter are always in random motion.

·  Chemical Energy: the energy stored in the chemical bonds in compounds. When these bonds are broken, the release energy can do work. All chemical compounds store energy.

·  Electrical: The energy associated with electric charges, these charges can exert forces that do work.

·  Electromagnetic Energy: a form of energy that travels through space in the form of waves.

·  Nuclear Energy: The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy.

o  Fission: a process that releases energy by splitting nuclei apart.

o  Fusion: release energy when less massive nuclei combine to form a more massive nucleus.

15.2 Energy Conversion & Conservation:

·  Energy can be converted from one form to another.

·  Energy conversion: the process of changing energy from one form to another

·  When energy changes from one form to another, the total energy remains unchanged even though many energy conversions may occur.

·  The work done by friction changes kinetic energy into thermal energy.

·  The law of conservation of energy states that energy cannot be created or destroyed.

·  The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls.

·  When friction is small enough to be ignored, an object’s mechanical energy does not change. If you apply the law of conservation of energy to a process, you obtain an equation for the conservation of energy.