ACTIVITY SHEETS PHYSICS AND CHEMISTRY 2 nd ESO NAME:

ACTIVITY SHEETS PHYSICS AND CHEMISTRY 2 nd ESO NAME: Lesson 8. ENERGY AND ITS TRANSFORMATION ACTIVITY 1 Answer whether they have energy and what changes they produce: a) Petrol. b) A roof tile. c) A battery. d) A rolling ball. e) A sandwich. f) Boiling water. g) A light beam. ACTIVITY 2 1.-Read carefully the different types of energy in the left column. Take into account that kinetic means motion, therefore a body has kinetic energy if it is in motion. On the other hand, potential energy is related to the position of a body, the higher the position of a body the bigger the effect when it collides against the floor. Kinetic energy Boiling water Potential energy A rolling ball Thermal energy A roof tile Chemical energy Petrol or a sandwich Electrical energy A light beam Light energy A battery Nuclear energy An Uranium mineral 1

2.-Write the symbol > or < between the sentences: a) Kinetic energy, Ec, is related to the movement of the bodies. Ec (air at rest) Ec (air in motion) b) Potential energy, Ep, is related to the position of the bodies. Ep (helicopter 400 m) Ep (helicopter on the ground) c) Chemical energy, Eq, is related to the type and amount of substance. Eq (1 L of petrol) Eq (1 L of water) d) Thermal energy, E T, is related to the temperature and the amount of substance. E T (1 L of water to 20 ºC) E T (1 L of water to 90 ºC) READING 1 Carbon, petroleum, the wind or the Sun, are sources of energy. This is very important: Sources of energy should not be confused with types of energy, like potential energy or kinetic energy. Sources of energy are the natural resources from which the human beings may obtain energy to be used in their activities. Look at the diagram below in which you can see both, types and sources. Question.-Classify the following sources of energy as renewable and non-renewable and besides, if polluting or non-polluting. a) Carbon b) Solar radiation c) Petroleum d) Wind e) Natural gas f) Tides g) Nuclear fuel h) Biomass i) Dammed water j) Internal heat in the Earth 2

ACTIVITY 3 TAKING ADVANTAGE OF THE KINETIC ENERGY OF THE AIR (WIND ENERGY) You can observe that the wind is capable of provoke important changes. The wind moves the papers scattered on the ground and raises the powder or the sand. A strong wind may cause serious destruction like pulling up trees, blowing off roofs, knocking down the telephone polls, etc. Moreover, what to say about the disasters a hurricane may cause? You know that the wind is air in motion. Therefore, we can say that the wind is air that has kinetic energy. The energy of the air is called wind energy [Energía eólica]. From long time ago, human beings have been trying to make the most of the energy of the wind. The sailing ships and the windmills are applications that traditionally have used this type of energy. Currently, windmills are used, however, instead of moving stone mills to make flour, as traditionally were used, they move a dynamo producing electricity. In the diagram, you can see a current windmill called wind turbine (in Spanish, aerogenerador ). This windmill has three blades each up to 15 metres long and when working at full throttle it supplies energy for 3.000 bulbs to light. Wind turbines can be noisy and may be considered unsightly so there is some environmental objection to wind farms, especially as the best sites are often in coastal or upland areas of great natural beauty. Question 1: What advantages and disadvantages are there when using wind energy? Besides the content in the text, you can use the concepts: polluting/non-polluting; renewable/non-renewable; reliable/nonreliable. Question 2: A skater of 80 kg slides on the ice at a speed of 54 km/h. Convert the speed into m/s and calculate the skater s kinetic energy. ACTIVITY 4 TAKING ADVANTAGE OF THE POTENTIAL ENERGY OF THE WATER (HYDRAULIC ENERGY) This is the name given to the water rushing through the hillsides of the mountains, in streams and rivers. In order to get a source of hydraulic energy, damps are built to store water, which get to reach a high level. These reservoirs, which are also used as water stores, let us take advantage of the gravitational potential energy of water to get electric energy, as you will study ahead. Reservoirs play a protective function since the energy that water has when heavy or torrential rainfall occurs may provoke destructive changes. With good management hydroelectric energy is a reliable energy source, however, there are risks connected with the construction of dams, and a variety of problems may result from the impact of a dam on the environment. Land previously used for forestry or farming may have to be flooded. Question 1: What advantages and disadvantages has the hydraulic energy? Besides the content in the text, you can use the concepts: polluting/non-polluting; renewable/non-renewable; reliable/nonreliable. Question 2: What is the potential energy of a child that is at the top of a slide 3 metres in height. The child s mass is 22 kg. 3

ACTIVITY 5 FUELS AND EXPLOSIVES Some substances called fuels and explosives have, due to their type of atomic bonds, a large amount of energy that is shown when burnt. A property of fuels is their heating value ( poder calorífico ), which represents the energy we can get from one kilogram of fuel when burnt. That is why there are fuels better than others for certain jobs. For example, fuels for cooking or keeping us warm should have a high heating value and besides, they must be cheap. The first fuels the human being used could be dead branches, dead shrubs or bushes, which are still used in poorly developed countries. Not a long time ago, the human beings discovered the existence of deposits formed from plants and animals remains, which over millions of years became what we know as coals. This represents a crucial moment in the technological development of humanity. Nowadays, together with other fuels, the coal is still used. *Average values In the second half of 19 th century petroleum and natural gas started to be used, although their widespread use happened starting the Second World War. Petroleum is not directly burnt, but it is the source of other products. Up to three thousand different products are extracted from petroleum, of which only a few are used as fuels: fuel oil (for industry), diesel oil (for lorries), paraffin or kerosene (for jet engines) and petrol (for cars). Question 1: The heating value of a type of petrol is 43.890 kj/kg. What is the meaning of this number? Show a fuel from the table that gives us more energy and another one that gives us less energy than this type of petrol. Question 2: How can we get or extract the internal energy of a fuel? Question 3: Explain what has more internal energy. a) 1 L of alcohol or 1 L of water, both at the same temperature. b) 1 Kg of iron to 800 ºC or the same piece to 20 ºC. Some fuels HEATING VALUE (kj/kg) Alcohol Butane Carbon* Fuel Oil* Petrol* Hydrogen Wood* Propane 32.186 49.324 28.500 42.200 43.680 142.120 16.720 50.160 ACTIVITY 6 FOOD: MORE THAN A FUEL When food is eaten, it reacts with the oxygen we breathe into our lungs and is slowly burnt. As a result, chemical energy stored in food becomes thermal energy to warm the body and kinetic energy for muscular movement. We need energy for several reasons. a) Operating. We need energy for moving, working, running, etc. b) Renewing tissues: Our skin is continuously changing, and the same happens to our hair, nails and the inner parts of our bodies. c) Growing: Children do not stop growing up until they become adults. Consequently, we must not eat anything. We need a mixed food in order to meet the needs of our bodies. The energy of food is usually measured in kilocalories, although the experts on nutrition call them big calories ( calorías grandes ) and sometimes, simply calorias. Therefore, when we read in food packages that 100 grams have as many calories, we have to understand that they are really kilocalories. Overfeeding is a problem in the developed world. Food with high values in energy are fattening and if more food is eaten than the body really needs, the extra is stored as fat. 4

However, in other parts of the Earth, there is a serious lack of food and the famine is the main cause of loss of life. Question 1: An adult, doing a usual work, needs, more or less, 2500 kcal every day. Does this mean that he would be properly fed with only one food, for example potatoes, eaten up to reach those 2500 kcal? Question 2: Calories and Joules are units of energy. You can convert into each other applying the relationship you have below. May you convert 2.500.000 calories into Joules? 1 calorie 4,18 Joules Question 3: In what way are alike or different the petrol needed for an engine to work and the food we need for us to work? READING 2 Have you ever heard this statement? Energy is never created or destroyed, it is only converted from one form to another. This is known as the Principle of Conservation of Energy. When an object is falling down from certain height, its potential energy is lower and lower, whereas its kinetic energy is higher and higher in such a way that the total amount of energy (Ec + Ep) is always the same. The total amount of energy in the Universe is constant. In other words, if somewhere in the Universe energy increases, at the same time there is a decrease. Look at the pictures below. The Ep (potential energy) gained by the bell when it is set in the tower will be equal to the Ei (internal energy) lost by the man. The Ep of the stone transforms into Ec as it falls down. Ep = m g h = Therefore, the final kinetic energy, E C = Here you have more examples: a) A car can move because it uses petrol, you know, chemical energy, which is transformed into motion, kinetic energy, and thermal energy due to the friction. Ei (petrol) Ec (car) + E T b) A battery lights a bulb, because chemical energy produced inside the battery is converted into light energy and thermal energy. Ei (battery) E light (bulb) + E T 5

ACTIVITY 7 1.-What type of energy is stored in food? 2.-State the principle of conservation of energy. 3.-Give an example of device that uses potential elastic energy 4.-Sometimes, you can hear on TV that petrol is energy. Do you thing this is correct? What should be said? (go to reading 1) 5.-Using a pulley system a sheep of mass 47 kg is slowly raised through 6,3 m. Find the gain in potential energy. 6.-If we droop the sheep of the previous question, what will be the kinetic energy of the poor animal when it reaches the ground? 7.-A car with a mass of 2450 kg is travelling at 38 m/s. Calculate its kinetic energy 8.-A bird of mass 3 kg flies at a height of 250 m and at a speed of 8 m/s. a) Calculate its kinetic energy, b) calculate its potential energy, c) convert into calories the results of both previous questions (take a look at activity 6, question 2). 9.-Calculate the kinetic energy and the potential energy of a bullet of 200 g if it displaces at a speed of 200 m/s and is 20 m above the ground. Watch out the units. 11.-Which of the next changes is impossible to happen? a) In a bulb: 100 J of electric energy are converted into 40 J of light energy. b) In a rifle: 200 J of internal energy of gunpowder are transferred to 250 J of energy of the bullet that is moving. c) In a carbon thermal power station: 280.000 J of internal energy of carbon are transformed in 70.000 J of electric energy. d) In a loudspeaker: 3 J of electric energy are changed into 0 5 J of sound energy. ACTIVITY 8 THE ELECTRICAL ENERGY A generator is a device that transfers to electrical energy other types of energy. The most important generator in industry is the dynamo. Its functioning is based on the property of producing electrical current through a metallic wire when the wire is moved near a magnet or a magnet is moved near a wire. Batteries are other generators, which transform internal (chemical) energy to electrical energy, and the solar cells, which convert sunlight (light energy) into electrical energy. On the right, you have a DYNAMO, which is a really simple device. It is a coiled metallic wire, which moves near a magnet. It is amazing that such a simple scheme is the basis for the production of electrical current that transfers to our houses an energy of high quality, in which our welfare and progress are based In other words, the production of electricity is based on getting the coil to turn in the dynamo, and the way to get it is what makes the difference among the several types of power stations. Apart from the way to make turn the dynamo, all the power stations are very similar. 6

What drives the dynamo in the hydroelectric power stations is the flow of water falling from top of the dam. Fuels like carbon, gas or fuel oil, are burnt in thermal power stations to produce heat that turns water into steam, and the pressure of the steam drives the dynamo. ACTIVITY 9 LIGHT ENERGY The energy falling on the Earth from the Sun is mostly in the form of light and in an hour equals the total energy used by the world in a year. For you to get an idea, in a sunny day, in a country like Spain, in 1 m 2 of surface is received in one hour as much energy as we can get from 1 kg of carbon or 1 L of petrol. Solar energy from the rays of the Sun is transformed into electrical energy (using solar cells), or used directly to heat eater (using solar panels). The hot water can then be used to wash or heat our homes. The main advantage of solar energy is that is inexhaustible. However, solar energy is less efficient in countries with fewer sunny days, and at higher latitudes where there are fewer hours of sunlight in winter (for example, in Scandinavia). Also, the solar panels must be very large in order to collect enough solar energy for them to be useful. 7

SOURCE ADVANTAGES DISADVANTAGES Carbon Petroleum Hydroelectric Wind energy Solar Nuclear Renewable / non renewable Polluting / clean Reliable / Non reliable Take up a lot of space or not Etc. 8