Extension Question 2

How do you calculate Potential energy?

Potential energy is calculated using this formula:
PE = mgh
PE = energy (measured in joules)
m = mass of object (measured in kilograms)
g = gravitational acceleration of the earth (9.8 m / sec2)
h = height above earth’s surface (measured in meters)

Example
Calculate the potential energy of a 5kg ball located 3m above the earth’s surface.

PE = 5 x 9.8 x 3
PE = 147 joules

How to calculate Kinetic Energy:
When an object moves it has acceleration therefore it has velocity.  The change of velocity means that there is kinetic energy.

The Equation is:
KE= ½ mv2­
KE= Kinetic Energy
M= Mass
V- velocity

Kinetic Energy Example:
Case 1: Determine the Kinetic energy of a 500kg roller coaster train which moves at a speed of 20 m/s.

M = 500 kg, V = 20 m/s
Step 1: Substitute the values in the below kinectic energy formula:
Kinetic Energy: Ek = ½ mv2
= ½ x 500 x 202
= 0.5 x 500 x 400
Kinetic Energy: Ek = 100000 Joules or 1 x 105 Joules
This example will guide you to calculate the kinetic energy manually.

Case 2: What is the speed of a 55 kg woman running with a kinetic energy of 412.7 J?
Ek = 412.7, M = 55 kg
Step 1: Substitute the values in the below Velocity formula:

Image

How can you calculate the velocity of an object when it loses height?

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Extension Three- How can you tell that the (swing) system is not 100% efficient?

swing

After gaining momentum, the swinger has two main options. These are to A) keep up the pace or B) allow themselves to slow down in order to get off.

If you go with option B), all you need to do is stop trying to swing. By doing this, your swing will eventually come to a stop, without actively dragging your feet through the ground.

Since an entirely efficient system recycles all energy within the action, a swing motion would have to never lose height in order to be 100% efficient.

Therefore, the action of swinging is not completely productive.

How does a child on a swing illustrate the Law of Conservation of Energy?

A child on a swing illustrates the Law of Conservation of Energy in a very clear and understandable way. When the child is at the highest point of the swing, the potential energy is at its highest. When the swing swoops down to the centre of the swing, the kinetic energy is highest. As it slowly climbs back up, the kinetic energy decreases as the speed decreases, and the potential energy increases with height. Click on the diagram below to see a visual representation of the process.

swanim

Energy Types

Potential Energy:
Dictionary Meaning:
The energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge, and other factors. (Harvard Dictionary)

Potential Energy is when the object is still.

Kinetic energy:
Dictionary meaning:
Energy that a body possesses by virtue of being in motion. (Havard Dictionary)

Kinetic Energy is when the object is moving.

Energy Transfer and Transformation

Why do you think it is important to understand how energy is transferred or transformed?  

Energy Transfer Definition

‘Energy transfer is the transfer of energy from one object or material to another’

-       Wikipedia 2013

Types of Energy Transfer

There are many different types of energy transfers including:

  • Radiant Energy (radiation)
  • Heat Conduction (travelling heat)
  • Convection (currents of warm air)
  • Mass transfer (hot material transferred to another location)
  • Electrical power transmission (wires carrying current)
  • Mechanical work (machines)

Energy Transformation Definition

‘Energy transformation or energy conversion is the process of changing one form of energy to another’

-       Wikipedia 2013

‘In physics, the term energy describes the capacity to produce certain changes within a system, without regard to limitations in transformation imposed by Entropy’

-       Wikipedia 2013

These are some common energy transformations:

Thermoelectric (Heat –> Electric energy)

Ocean thermal energy (Heat –> Electric energy)

Fire (Chemical energy –> Heat and Light energy)

Hydroelectric dams (Gravitational potential energy –> Electric energy)

Heater (Electric energy –>Heat)

It is important to understand how energy is transferred or transformed or transformed, so that you are able to use energy to it’s full potential and not loose / waste any in the process. As a physics student it is helpful to understand how energy is transferred / transformed when reading related materials and trying to apply your knowledge.  

Energy Transfer Post

This image shows an example of an energy transfer.

Law of Conservation of Energy

What is the Law of Conservation of Energy?
“All the energy before must be equal to all the energy after”
Therefore, no energy can be lost or created, rather transforms from one type to another.

How can it be expressed symbolically?
Eti=Etf
Where the initial total of energy (Eti) is equal to the final total of energy (Etf).