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Energy Transformations

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. Use $E_{k} = \frac{1}{2}mv^{2}$
  3. Explain the conservation of mechanical energy in free fall situations (e.g. ball sports)

Types of Energy


What do they have in common?


Conservation of Energy

Energy cannot be created or destroyed, only transformed.


Written as an equation, this can mean:

\begin{aligned} E_{k} &= E_{p} \
\frac{1}{2}mv^{2} &= mgh \end{aligned}

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



Pātai

Mr Le Sueur has mass 71kg and has climbed a tree 4.5m tall to jump into a lake. How fast will he be traveling when he hits the water?


Whakatika

\begin{aligned} E_{p} &= mgh = 71 \times 10 \times 4.5 = 3195J \
E_{k} &= E_{p} \
E_{k} &= \frac{1}{2}mv^{2} \
3195 &= \frac{1}{2} \times 71 \times v^{2} \
\frac{3195 \times 2}{71} = 90 &= v^{2} \
\sqrt{90} = 9.49ms^{-1} &= v \end{aligned}


Tūhura: Marble Drop

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

Akoranga 22 Mahi Tuatahi

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.


Akoranga 23 Mahi Tuatahi:

  1. Write the date in your books
  2. Open the Quizlet on Google Classroom and complete “Match” three times
  3. Get ready to play the Quizlet Live

Ngā Whāinga Ako

  1. Identify energy changes.
  2. Use $E_{k} = \frac{1}{2}mv^{2}$
  3. Explain the conservation of mechanical energy in free fall situations (e.g. ball sports)

Write ngā whāinga ako in your books


Pātai: Do you recall the law of conservation of energy?


Conservation of Energy

Energy cannot be created or destroyed, only transformed

We investigated this last term by calculating the gravitational potential energy of a marble at the top of a tube and predicting how fast it would be moving at the bottom of the tube if all of the $E_{p}$ was transformed into kinetic energy $E_{k}$.


Energy cannot be created or destroyed, only transformed


Pātai: Mahi Kāinga Booklet Q40