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.
- 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.
- Describe the type of energy at the top, the middle and bottom of the fall.
- Calculate the potential energy at the top.
- Calculate his maximum speed. At what position does he have this speed?
- 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 🔗
- Come over to the demo bench to see the setup
- Open Google Classroom and do the tūhura!
Whakawai / Practice 🔗
- sciPad 62-63
- Mahi kāinga booklet Q40
- Mahi kāinga booklet Q41