Energy Transfer Tracker

Energy is only ever moved

Here is the one idea the whole topic is built on, and it is worth getting straight first. Energy is never made out of nothing, and it is never destroyed. It is only ever MOVED from one place to another. Those places are called STORES. A moving object holds energy in its kinetic store; something high up holds it in a gravitational store; a battery or a lump of food holds it in a chemical store; a hot object holds it in a thermal store. When something happens, energy shifts from one store to another along a PATHWAY. It can be moved by a force pushing something, by an electric current, by heating, or by radiation such as light or sound. ⭐ And because energy is only moved, never made or lost, you can TRACK it. Add up the energy in all the stores before a change, add it up after, and you get the same total. This is called conservation of energy. That turns any question into bookkeeping. Where did the energy start, where did it end up, and how did it get there? Carry that through everything that follows: which store did the energy start in, which store did it end in, and how did it get there?

Words for tracking energy

Six words the topic turns on, defined and nothing more.

Track a falling ball

A ball is held high, then dropped, and finally lies still on the ground. Put the energy changes in order.

• At the top, the energy is in the ball gravitational store
• As it falls, that energy moves into the kinetic store and the ball speeds up
• When it hits the ground, the kinetic store empties in an instant
• The energy ends up in the thermal store of the ball and the ground, which warm very slightly

Where did the energy go

A moving toy car rolls along the floor, slows down, and stops. Its kinetic store is now empty. Since energy cannot be destroyed, where has that energy gone?

• Into thermal stores: friction between the car and the floor has warmed them very slightly, so the energy is spread out, not gone
• It has been destroyed, because the car has stopped
• It was used up, so there is none left anywhere
• It went back into the gravitational store

A store against a pathway

These two words are easy to muddle, and keeping them apart is half the topic.

Which energy facts hold

Select the TWO statements that are true.

• The total energy before a change is equal to the total energy after it
• When energy seems to disappear, it has usually moved into thermal stores of the surroundings
• A battery creates new energy when it powers a device
• Once energy has been used, it no longer exists

How to track any transfer

A routine for almost any energy question. ⭐ Name the store the energy starts in. Ask where the energy is at the beginning: is something moving, raised up, hot, or holding fuel? That is the starting store. ⭐ Name the store it ends in. After the change, where has the energy gone? Very often some of it ends in thermal stores, spread into the surroundings, which is why energy seems to disappear when it has only spread out. ⭐ Name the pathway between them. Was the energy moved by a force, by an electric current, by heating, or by radiation? That is how it got from the first store to the second. ⚠️ And use the modern words. There is no store called heat energy, light energy or sound energy. Say the THERMAL store, and transfer BY HEATING or BY RADIATION. Getting this language right is itself worth marks. Do those three, and conservation checks your work: whatever was in the stores at the start must all be accounted for at the end.

Match each store to an example

Money never vanishes

Step away from physics and think about money in a set of bank accounts. You have a current account, a savings account and a cash tin. Money can sit in any of them, and it can be moved between them: a transfer online, cash withdrawn, a standing order set up. ⭐ Here is the key thing. When you move fifty pounds from savings to your current account, no money is created and none is destroyed. The savings account goes down by exactly what the current account goes up by. The TOTAL across all your accounts is unchanged by the move. ⚠️ If you added up every account before the transfer and added them up after, you would get the same figure. A move only ever shifts money about; it never changes the total. And if some of it seemed to disappear, you would not say it was destroyed. You would look for the account it went into, perhaps one you had forgotten. Energy works in exactly this way. The accounts are the places energy sits, the transfers are the ways it moves, and the total never changes, however much it is shifted around. When energy seems to vanish, it has simply moved into an account you were not watching, usually a warm one.

Complete the energy facts

Energy is held in a _____, and it moves from one to another along a _____. It is never made or destroyed, only moved, so we say energy is always _____. The energy an object has because it is moving is held in its _____ store.

Balance the energy books

A battery transfers 500 joules from its chemical store. Of that, 350 joules end up in the kinetic store of a toy, and the rest ends up in thermal stores. Since energy is conserved, how many joules end up in the thermal stores?

Build the conservation rule

Assemble the rule that energy is conserved.

The energy tracking run

Five questions on stores, pathways and conservation. Three lives.

Track three changes

Three everyday changes. For each, track where the energy goes.

• A drawn bow is released and the arrow flies off. Where does the energy start, and where does it go?
• An electric kettle boils water. Track the energy from the mains to the water.
• A student says a wind-up torch proves energy can be created, because winding it makes light appear from nothing. How would you correct them?

Explain what happens to the energy

A friend thinks that when a bouncing ball finally stops, its energy has been destroyed. Explain, using stores and pathways, what has really happened and why energy is still conserved.

• Explain what conservation of energy means
• Name the store the ball energy starts in when it is held high
• Track the energy through the stores as it falls, bounces and finally stops
• Explain where the energy ends up, and why it seems to have disappeared
• Finish by explaining why the total energy is the same at the end as at the start