Exercises: Forms of energy and transformations

State what form of energy each of these things has:

1. a) A kite flying high at the beach.
2. b) Water stored in a reservoir, at the top of the dam.
3. c) A new, unused battery.
4. d) The flame of a camping stove.

Vera has left her book on the top shelf of the bookcase, as shown in the figure.

1. a) What form of energy does the book have because it is so high up?
2. b) If the book falls, into what form of energy is that energy transformed while it falls?

At the neighborhood party they have connected some large speakers, like the one in the figure.

1. a) What form of energy enters the speaker through the cable?
2. b) What form of energy comes out of it and makes us dance?

Complete the sentence with the missing words: "Energy is neither created nor destroyed, it is only $\dots$ from one form to $\dots$". Then give an everyday example in which this happens.

Yasmin has a sandwich for breakfast and then plays a handball game, in which she runs and sweats a lot.

1. a) What form of energy was stored in the breakfast food?
2. b) Name two forms of energy into which her body transforms it during the game.

Match each form of energy to its example and write out the four complete pairs:

1. a) Nuclear energy.
2. b) Wind energy.
3. c) Sound energy.
4. d) Electrical energy.

Examples: the doorbell, a windmill, the wall outlet and the Sun.

The wind turns the colorful pinwheel that Mateo has planted in the garden, as shown in the figure.

1. a) What form of energy does the moving air have?
2. b) What form of energy do the pinwheel blades have as they rotate?

In a thermal power plant, natural gas is burned to generate electricity. The diagram of the plant is as follows:

The chain of transformations is out of order:

1. a) Electrical energy.
2. b) Chemical energy of the gas.
3. c) Kinetic energy of the turbine.
4. d) Thermal energy of the water vapor.

Write it in order using arrows, from the gas to the power grid.

In Daniela's yard there is a solar street light that turns on automatically at night.

1. a) What form of energy does it collect from the Sun during the day?
2. b) In what form is that energy stored in the light's battery?
3. c) Write the chain of transformations that energy undergoes at night, from the battery to the light.

In an old light bulb, out of every $100\ \text{J}$ of electrical energy, only $10\ \text{J}$ are converted into light. The figure shows this energy flow.

1. a) How many joules are lost as heat?
2. b) Why does it burn to touch one of these light bulbs after it has been on for a while?

Liam goes down a long hill on his bike without pedaling, and brakes when he reaches the bottom, as shown in the figure.

1. a) What energy transformation takes place while he goes down and gains speed?
2. b) When braking to a stop, into what form of energy is the kinetic energy transformed?

Sophia swings on a swing higher and higher. The figure shows the swing at the highest point (A) and at the lowest point (B).

1. a) What form of energy does she have at the highest point, where she stops for a moment?
2. b) And what form of energy does she have when passing through the lowest point?
3. c) If nobody pushes her, she goes less high each time. What "thief" takes away part of the energy and into what form does it convert it?

Bruno's camping flashlight works on batteries.

1. a) Write the complete chain of transformations, from the energy stored in the battery to the light that comes out.
2. b) In addition to giving light, the bulb warms up a little: what other form of energy appears?

An old light bulb transforms $100\ \text{J}$ of electrical energy into $10\ \text{J}$ of light. An LED bulb transforms the same $100\ \text{J}$ into $40\ \text{J}$ of light. The figure compares the energy flow of the two bulbs.

1. a) How much energy does each one lose as heat?
2. b) Which one would you choose for your home? Justify your answer using the data.
3. c) In summer it is hot at home. Explain why having many old light bulbs switched on can make the air conditioning use even more energy.

On a roller coaster, the car is stopped at the top of a $30\ \text{m}$ hill and then drops almost to the ground, as shown in the figure.

1. a) Describe the energy transformation that takes place on the way down.
2. b) If there were no friction at all, to what height could it climb on the next hill? Why?
3. c) In reality it always climbs a little less. Into what has the "missing" energy been converted?

An electric car is charged at a house with solar panels, as shown in the figure.

1. a) Write the complete chain of transformations, from sunlight to the motion of the car. It must include at least four forms of energy.
2. b) State two moments in that chain where some energy is lost as heat.
3. c) Some electric cars recharge the battery slightly when braking. What energy transformation do they take advantage of to do this?

A friend tells you: "It doesn't matter if you leave the light on, because energy is not destroyed, it is only transformed."

1. a) Is it true that energy is not destroyed?
2. b) Explain why, even so, this reasoning is wrong: think about what form of energy the bulb's energy ends up as and whether it can be reused.
3. c) Add another argument related to energy sources or money.

The International Space Station has huge solar panels as well as large batteries.

1. a) It orbits the Earth once every $90\ \text{min}$ and part of the journey is in shadow. Why does it need batteries if it already has panels?
2. b) Write the chain of transformations from sunlight to the onboard computer when the station is in shadow.
3. c) Computers and appliances heat up: what form of energy is in excess and must be radiated into space?

A pumped-storage hydroelectric power plant pumps water at night from a lower lake to an upper one, using cheap excess electricity. During the day it releases the water and generates electricity. The diagram of the installation is as follows:

1. a) Write down the sequence of transformations at night, when pumping the water up, and during the day, when releasing it.
2. b) In the process, some energy is lost as heat. Does this contradict the idea that energy is conserved? Explain your answer.
3. c) If it loses energy, why is it worthwhile for the power plant to operate like this? Think about how electricity does not cost the same at $3$ in the morning as at $8$ in the afternoon.

A gymnast jumps on a trampoline.

1. a) What form of energy does she have at the highest point of the jump?
2. b) Describe the complete transformations from the moment she falls until she rises again: what happens to the energy when the trampoline stretches and when it recoils?
3. c) To jump higher and higher, the gymnast "pushes" with her legs on each bounce. Where does her body get this extra energy from?