Conservation of Mechanical Energy

CONCEPT

Mechanical Energy is the energy associated with motion. Mechanical Energy is divided into potential and kinetic energy.

Potential energy: the energy stored within an object.

For example, a stretched bow of an archer.

The formula for potential energy is
mass x gravitational acceleration x height

Kinetic energy: the energy possessed by the object because of its motion or because of its velocity.

For example, a person running.

The formula for kinetic energy is 0.5 x mass x velocity2





EQUATIONS + SOLUTION

Kinetic Energy
Determine the Kinetic Energy of a rabbit hopping with velocity of 2 m/s and 12 kg mass.
KE= 0.5 x m x v2
KE= 0.5 x 12 kg x 22
KE= 24 Joules

Potential Energy
Determine the Potential Energy of a chandelier hanging from the ceiling with a mass of 4 kg, hanging 5 m high and 12 m/s2 for the gravitational acceleration.
PE= m x g x h
PE= 4 kg x 12 m/s2 x 5m
PE= 240 Joules


CONSERVATION OF ENERGY

- It is the transformation from one form of energy into another.
- Instruments or objects which help the transformation are called converters.
- Example: a lamp turned on changes electrical energy into light and thermal energy.

Sources of Energy

  Sources of energy which are not renewable: cannot be regenerated after it is used up.
Examples are fossil fuel, coal, and natural gas.

  Sources of energy which are renewable: Source of energy which can be regenerated when it is used up.

 1. Wind Energy
- Always available in nature.
- Example: windmill. Disadvantages are they have big construction size and needs a high speed wind.


2. Waterfall Energy
- Moving water can rotate a turbine which further produces energy.
- Moving water has sufficient potential and kinetic energy.
- Example: Hydroelectric power plant. It is electricity generated from the energy of moving water.


3. Solar Energy
- Easy to get and pollution free
- It will never run out because the sun always beam to earth
- Example: calculator using solar energy



4. Nuclear Energy
- Fission: the splitting process of a heavy nucleus into two lighter nuclei and a huge energy release. Examples are nuclear power plant.
- Fusion: the process of joining the nuclei of atoms and a huge energy release.

5. Tidal Energy
- Example is a dike, used to gain electricity in a tidal power plant.

6. Geothermal Energy
- Produced from the heat of earth.
- A power plant which uses geothermal is called a geothermal power plant.

7. Biomass Energy
- The energy which comes from plants to animals.
- Plants are processed into alcohol to get biomass energy.

Self Assessment 15.6

1. Fossil fuels are considered as a source of energy which is not
renewable. Why is it so?
Fossil fuels take millions of years to form under the surface of earth, and when its burnt, they are finished.


2. What happens if the fuel consumption is not spared? 
When the fuel consumption is not spared, it will eventually run out and we will have to find alternatives.

3. Write down the dangerous issues of having a nuclear power plant. 
- Radioactive

 materials can come into contact with people mainly through accidents in nuclear power plants, accidents in transporting radioactive materials, and escape of radioactive wastes.

- 

Radiation can penetrate deep inside the human body where they can damage cells and thereby initiate a cancer. They can also cause genetic diseases in offsprings.

4. According to your opinion, in order to produce electrical energy, what is the best energy that fits with the current situation and is pollution free?
I think solar energy is the best energy that fits with the current situation. Solar energy is easy to get and it is pollution free and often noiseless. The sun will always beam onto Earth so this energy will never run out.

5. Write your suggestion in order to produce a very high temperature, so that a large amount of electricity can be generated from the use of seawater.

From the tidal energy of the seawater, we can convert it into electrical energy by putting a wave energy converter.

http://diditsmile.blogspot.com/2012/09/menghasilkan-energi-listrik-dari.html
http://www.physics.isu.edu/radinf/np-risk.htm
http://wiki.answers.com/Q/Why_are_fossil_fuels_considered_non-renewable

Chapter 3.1, Work

2. Work= F x D

             = 5000 N x 3000 m

             = 15 000 000 J

4. Work= F x D

    Distance= W ÷ F

                  = 20 000 J ÷ 340 N

                  = 58.82 m

6.  Mass= 100 kg

     Distance= 60 m

     Work= 1000 N x 60 m

              = 60 000 J

8.  Distance= 0.8 m

     Mass= 62 kg

     Work= F x D

              = 620 N x 0.8 m

              = 496 J

10. Force= 300 N

      Distance= 750 m

      Work=? 

(a) Friction=200N                                              (b) Friction= 300N

     W= (F1-F2) x d                                                  W= (F1-F2) x d

         = (300N-200N) x 750 m                                    = (300N-300N) x 750 m

         =  75 000 J / 75 kJ                                              = 0 J    

   

Energy

  People do work (running, walking, etc.) because they have energy. So, energy is defined as the ability to do work. The important thing about energy is that it is conserved, cannot be created or destroyed.

   For example, if object 1 hits object 2, the energy from object 1 goes to object 2 and the molecules in object 2 can cause the energy to vibrate, or go around the room, etc. The energy doesn't disappear.

Energy can come in different forms.

                         Chemical: Energy contained within food, your body, and fuel. The examples are gasoline filled up in a car, and batteries.

 Thermal: Vibration and movement of the atoms and molecules within substances. Some
examples are water boiled in a kettle and rubbing your hands until it feels warm.

                                 Sound: Energy created from the vibration of air particles around a sound source. Some examples are clapping your hands and a plane taking off.

 Light: Energy created by the radiation of electromagnetic waves. Examples are a
fire and the sun shining.

                                   Electrical: Energy created from the presence and flow of electric charge. Lightning is an example of electrical energy in nature and also stroking a cat with long fur.

 Nuclear: Energy released from the reaction of the radioactive matters. The examples 

are atomic and hydrogen bombs and also the sun (the energy is transmitted from sun

to earth in the form of electromagnetic radiation).

Mechanical: Energy associated with motion.

 1.  Potential energy, the energy stored within an object.

Spring potential energy - an archer's bow and a sling shot is two examples because 

when someone pulls it, energy is stored within it until it is released.

Gravitational potential energy - an apple hanging on a tree and a swing
are two examples. Both examples have gravitational potential energy because of the position.
The potential energy within the objects relates to its distance above ground.

2.  Kinetic energy, the energy possessed by an object because of it's motion/movement.

An object falling off of a table and a water falling from a tap water are some examples.

ball rolling down a slope
- kinetic and potential energy-

An apple hanging from a tree
-potential energy-

Resources:




- http://plainenglish.viewshare.net/physics/mechanics/energy.shtml
- http://www.nmsea.org/Curriculum/Primer/forms_of_energy.htm
- http://www.eia.gov/kids/energy.cfm?page=about_forms_of_energy-basics
- www.wisegeek.com/what-is-electrical-energy.htm

What is work?

Work involves force and displacement of objects. It can also be defined as a transfer of energy. So to do work, there are some requirements:
- a force must cause displacement
- a force must have the same direction as displacement

The formula of work is force times distance because work is the application of a force over a distance.
(Force: W x D)
The unit of measurement for force is N (Newtons), distance is m (meters), and work is J (Joules).

Examples of work:
1. A woman is pushing a trolley. She transfers force to the bed until it moves, so it is considered as work.
2. Two men are lifting a box from the floor, they are producing force so the box is lifted.

Sources:
 http://www.edinformatics.com/math_science/work_energy_power.htm