Energy Transformations

11SCI - Mechanics

Finn Le Sueur

2024

Akoranga 21: Mahi Tuatahi:

  1. Write the date in your book
  2. Brainstorm on the board what types of energy are there?

Ngā Whāinga Ako

  1. Identify energy changes.
  2. Explain the conservation of mechanical energy in free fall situations (e.g. ball sports)

Types of Energy

  • Gravitational potential energy
  • Heat energy
  • Sound energy
  • Light energy
  • Elastic potential energy
  • Electrical energy etc.

What do they have in common?

  • All energy is measured in Joules (\(J\)).
  • A transfer of energy is called work, measured in \(J\).

Conservation of Energy

Energy cannot be created or destroyed, only transformed.

  • This means that gravitational potential energy can be transformed into kinetic energy, and kinetic energy into other forms of energy.
  • It is always taken from somewhere, never created from nothing.

Written as an equation, this can mean:

\[ \begin{aligned} E_{k} &= E_{p} \cr \frac{1}{2} \times m \times v^{2} &= m \times g \times \Delta h \end{aligned} \]

In fact, we can make any two energy equations equal to each other! E.g. Spring potential energy and kinetic.

  • We can convert one type of energy into another through mathematics!
  • This is only true in a frictionless world where no energy is lost through heat/sound/light

Pātai

Mr Le Sueur has mass 71kg and has climbed a tree 4.5m tall to jump into a lake.

  1. Describe the type of energy at the top, the middle and bottom of the fall.
  2. Calculate the potential energy at the top.
  3. Calculate his maximum speed. At what position does he have this speed?
  4. Calculate his speed half way down the fall.

Whakawai / Practice

Read page 55 and 56 of your sciPAD to remind yourself of some types of energy and how it is transformed between different types.

Then answer Question 1 on page 59.

In Physics we live in an idealised world where friction does not exist and energy is transformed with 100% efficiency.

This means that 100% of elastic potential energy is converted into kinetic energy, in the case of the rubber band.

It means that 100% of gravitational potential energy is converted into kinetic energy in the case of a sky diver.

Tūhura: Marble Drop

  1. Come over to the demo bench to see the setup
  2. Open Google Classroom and do the tūhura!

Whakawai / Practice

  • sciPad 62-63
  • Mahi kāinga booklet Q40
  • Mahi kāinga booklet Q41