## Akoranga 21: Mahi Tuatahi:

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

## Ngā Whāinga Ako

- Identify energy changes.
- Use $E_{k} = \frac{1}{2}mv^{2}$
- 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} \

\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.

- 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. How fast will he be traveling when he hits the water?

- Starts with $E_{p}$, so calculate it
- Then transformed all to $E_{k}$, so put known values into $E_{k}=\frac{1}{2}mv^{2}$

#### 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

- Come over to the demo bench to see the setup
- 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:

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

## Ngā Whāinga Ako

- Identify energy changes.
- Use $E_{k} = \frac{1}{2}mv^{2}$
- 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

- This means that we can say $E_{k} = E_{p}$
- In words, all kinetic energy is transformed into potential energy, or vice versa.

### Pātai: Mahi Kāinga Booklet Q40

- Open mahi kāinga booklet 40
- 40a is an achieved level question
- 40b is an excellence level question
- start by identifying the change in energy
- then use it to calculate the speed if all of that energy is transformed into kinetic energy