Energy

Chapter 15 and 16

What is energy?

Energy is the ability to do work. When work is done on an object, energy is

transferred to that object Energy is measured in Joules

There are 2 basic types of energy Kinetic energy Potential energy

Kinetic Energy

This is energy of Motion Anything that moves has kinetic energy.

Kinetic Energy = ½ mass·velocity2

KE = ½ mv2

*note that doubling the mass doubles the KE but if you double the velocity, the KE quadruples.

Potential Energy

Energy that is stored as a result of position or shape. A rock at the top of a mountain has a lot of

energy as compared to a rock that is at the base.

A stretched rubber band has a lot of potential energy as compared to one that is not stretched.

There are 2 types of Potential energy Gravitational Elastic

Gravitational Potential Energy

Energy that results from an objects height. (like the rock on the mountain example)

PEg = mass·gravity·height

PEg = mgh

Elastic Potential Energy

This is the potential energy of objects due to their shape. Elastic objects tend to go back to their original shape after they have been stretched or compressed.

Forms of energy

There are 6 major forms of energy.1. Mechanical

2. Thermal

3. Chemical

4. Electrical

5. Electromagnetic6. Nuclear (not “nuculer” like Pres. Bush says)

Mechanical Energy – motion and position of everyday objects. Sum of objects potential and kinetic energy.

Thermal Energy – sum of all potential and kinetic energies of an objects subatomic particle.

Chemical Energy – energy stored in chemical bonds in compounds.

Electrical Energy – energy associated with electrical charges.

Electromagnetic energies – travels through space in the form of waves.

Nuclear Energy – The energy stored in atomic nuclei.

Energy Conversion

Energy can be converted from one form to another.

A stone on a mountain top. The stone has high PEg and if it begins to fall it will convert its PEg into Kinetic energy until it hits the ground where It no longer has any PE.

Conservation of Energy

It’s a law! Energy cannot be created nor destroyed. Energy can only be converted into other

forms.

Energy IN = Energy OUT

Energy Conservation in Pendulums

As a pendulum swings, energy is constantly being converted from one form to another. At the highest point when the pendulum is

changing directions, the pendulum experiences maximum PE.

At the very bottom of the swing where the pendulum is moving the fastest, the pendulum experiences maximum KE.

Energy conservation in a pole vault. When a pole-vaulter runs toward the pit, he or she is

gaining KE. Once the athlete reaches the pit they plant their pole

and it bends, thereby converting their KE into Elastic PE.

This elastic PE is then converted back into KE and propels the athlete upwards where he or she gains Gravitational PE.

Now, at the top this Gravitational PE is at its maximum and then begins to convert to KE again until the athlete lands safely on the pad.

Conservation of Energy in a match

Chemical energy(PE) in your muscles is converted into mechanical energy(KE) when you strike the match.

This KE is converted into thermal energy by friction with the sandpaper.

This thermal energy starts a chemical reaction and the chemical energy(PE) of the match is converted into thermal energy and electromagnetic energy.

Thermal Energy and Heat

Heat is the transfer of thermal energy from one object to another because of a temperature difference

Heat always flows from hot to cold.

Heat Transfer

Heat can be transferred in several ways. Conduction Convection Radiation

Conduction

Transfer of thermal energy or heat by objects that are touching Conduction is faster in objects or medium

whose molecules are closer together. For example metal conducts heat more efficiently than air.

Convection

Transfer of heat when particles of a fluid move from one place to another. Convection is how our earth redistributes heat.

(magma, water, and air)

Radiation

Transfer of energy by waves in space. No medium is necessary for radiation to

occur. This is the method by which we feel energy from the sun or see the stars.

As an objects Temperature increases, it radiates more energy.

Specific Heat

Amount of Thermal energy needed to raise the temperature of one gram of material by one degree Celsius.

Measured in joules per gram per degree Celsius. J/g·°C

The Higher an objects specific heat means that it will be more resistant to temperature change.