Energy Unit

Adapted from Motion, Forces, and Energy textbook Copyright 1997 Prentice-Hall Inc.

What is Energy?

What is energy?  Energy is not matter.   Matter is anything with mass and volume 

We now know how to change matter into energy though. How?

 We live in an ocean of energy. Energy is all around us, we are surrounded.

Energy

Energy:

  The ability of something to cause change

 

The ability to do work

Measured in joules (j)

  Unit: Energy (j) same as work (j)

5 Forms of Energy

5 forms of energy:1. mechanical

2. heat

3. chemical

4. electromagnetic

5. nuclear

Mechanical Energy

Mechanical Energy

Energy associated with motion

Heat Energy

Heat Energy

The internal motion of the atoms is called heat energy.

The faster the atoms move the more heat energy they have.

Rub hands together mechanical to heat

Chemical Energy

Chemical Energy

Energy required to bond atoms together.

bonds are broken,

chemical energy is released

Electromagnetic Energy

Electromagnetic Energy

  Moving electric charges

Nuclear Energy

Nuclear Energy 

Nucleus -(protons and neutrons)

nucleus splits, nuclear energy is released in the form of heat and light energy

Potential Energy

Potential Energy (PE):  Stored energy due to position Examples: rock on a cliff, battery, food,

gasoline, stretched rubber band, apple hanging in a tree

 

Elastic Potential Energy

Elastic PE: Energy stored by something that can

stretch or compress (ex. rubber band, spring)

 Ex: shoot an object with rubber band. Farther you stretch the rubber band, the faster the object travels, therefore greater KE.

Elastic Potential Energy

Do rubber bands have energy to do work?

(un-stretched rubber bands no energy) 

Stretch rubber band—Does it have energy to do work?(stretched rubber bands have energy)

 Where is the energy when the rubber band is stretched?

(it is in the rubber band) 

What happens to the energy when the rubber band is released?

(it is converted into motion -- KE)

Gravitational PE

Gravitational PE (GPE):

 

Energy stored by objects that are above the earth’s surface (objects that can fall)

 

Depends on mass, acceleration and height

 

GPE increases with height

Gravitational PE

GPE = mass gravity height

GPE = m g h = weight height

  GPE = m (kg) 9.8 m/s2 h (m)

j = 1 Nm

 

Kinetic Energy

Kinetic Energy (KE):  Energy in the form of motion

 

Depends on mass and velocity of moving object.

  Object in motion has ability to do work

Kinetic Energy

KE = ½ mass velocity2

 

KE = m V2

2

(j) = (kg) (m2/s2)

 1 j = 1 kg m2/s2

Kinetic Energy

Double mass and you double energy

  Double velocity = 4 times the KE

As velocity is squared, increase velocity and KE greatly increases.

Which would hurt more? Double mass of bowling ball or double the velocity? Explain.

Roller CoasterPE: 354kJKE: 0kJV: 0m/s

PE: 177kJKE: 177kJV: 26.2m/S

h=70m

Potential energy becomes Kinetic energy.

h=35m

PE: 0kJKE: 354kJV: 37.1m/S

PE: 0kJKE: 354kJV: 37.1m/S

Kinetic energy can become Potential energy.

Energy analogy

When energy is transferred, it can transform (change form) but it still remains energy.

 

 Analogy:How is energy like money?

  When money is transferred from one person or place to another it can change form (transform) but it still remains money.

Energy Transformations (ball)

Demonstrate: how bounce height of ball becomes lower and lower each time it bounces. Have students infer why this happens.

Each time the ball bounces, part of its energy is transformed into other forms of energy, such as thermal (heat) energy, sound energy and vibrations in the ground. In addition, some energy is absorbed by the ball. Therefore, it will never bounce as high as the initial drop height.

Energy Transformations

Ex: A light bulb is a device that transforms electrical energy into electromagnetic (light) energy and thermal energy

 Chemical energy (coal) heat energy

(burn to create steam) mechanical energy (steam is used to turn turbines) Electromagnetic energy (generates electricity) heat energy (blow drier, oven)

Law of Conservation of Energy

The law of Conservation of Energy:

 

Energy cannot be created or destroyed. It may be transformed from one form into another; however, the total amount of energy in the universe remains constant. (Transformers)

Law of Conservation of Energy

Energy conversions occur without a gain or loss in energy

Energy into a system = energy out of a system

 Due to friction, energy might seem to be lost, but it has changed into thermal energy.

 .

Bibliography

staffweb.psdschools.org/jbarnaby/8_pwrpt/Energy%20unit%20pwr%20point.ppt