Energy Chapter 5

Energy is the ability to do work or cause change What is Energy 5.1 Energy is the ability to do work or cause change Work is done when a force moves an object through a distance. W = F x D

Work and Energy When an object or living thing does work on another object, some of its energy is transferred to that object Therefore: Work can be thought of as the transfer of energy. When energy is transferred, the object upon which the work is done gains energy. Energy is measured in Joules (same unit as work)

Power and Energy Power is the rate at which work is done If the transfer of energy is work, then power is the rate at which energy is transferred OR the amount of energy transferred in one unit of time Power = Energy transferred Time

Power & Energy Power is involved whenever energy is being transferred. Calm breeze vs. Tornado Power of both is the rate of energy transfer to lift a leaf a certain distance Tornado has the same energy transfer, but with more power because it transfers the energy at a quicker rate.

Types of Energy Two basic types of energy Kinetic Potential Type of energy depends on if the object is moving or not. A moving object can do work when it strikes another object and moves it some distance The energy an object has due to its motion is called kinetic energy Greek word kinetos = moving

Factors affecting Kinetic Energy (KE) Kinetic energy depends on Mass Velocity KE increases as mass increases KE increases as velocity increases

Calculating KE KE = ½ x mass x velocity 2 Does changing the mass and velocity have the same affect on KE? NO – changing the velocity has a greater effect on KE than changing the mass by the same factor. WHY? – because velocity is squared. Therefore, doubling the mass will double the KE, but doubling the velocity will quadruple the KE.

Potential Energy (PE) An object does not have to be moving to have energy Some objects have stored energy Result of their shapes or positions Lift a book off the floor to your desk Compress a spring to wind a toy. Energy has been transferred to those objects in both examples and is stored. May be used later when the book falls to the floor or the spring unwinds. Stored energy as a result of shape or position of an object is potential energy. This type of energy has the “potential” to do work.

Gravitational Potential Energy (GPE) Defined as potential energy related to an objects height. GPE equaled to the work done to lift the object Recall: work = force x distance The force used to lift the object equals the weight of the object The distance the object is moved is the object’s height

Gravitational Potential Energy (GPE) Formula to calculate GPE GPE = mass x gravity x height Simplified as GPE = weight x height REMEMBER: weight = mass x force of gravity Gravity On Earth = 9.8 m/s2

Example:

Calculate If the ski jump is 40m high, what is the GPE of the Green skier = 600N Red Skier = 500N 500 Newtons x 40m = 20,000 J GPE 600 Newtons x 40m = 24,000 J GPE

Elastic Potential Energy (EPE) An object gains a different type of potential energy when it is stretched Elastic potential energy – the potential energy associated with objects that can be stretched or compressed

Formula to calculate Elastic potential energy EPE = ½ kx2

Chapter 5-2 Forms of Energy Energy comes in many forms Mechanical energy – associated with the position and motion of an object A combination of potential and kinetic Calculation: Mechanical Energy = Kinetic energy + Potential Energy

Example of ME calculation A football thrown by a quarterback has BOTH PE and KE. The higher the ball is thrown the greater the PE, the faster it is thrown the greater the KE. PE = 32J KE = 45 J Mechanical Energy (ME) = 77J (32+45) An object with mechanical energy can do work on another object Mechanical energy is the ability to do work. The more ME an object has the more work it can do.

Other forms of energy These other forms are associated with the particles that make up objects. These particles are too small to be seen. (atoms & molecules) Thermal energy Electrical energy Chemical energy Nuclear energy Electromagnetic energy

Thermal energy All objects are made up of atoms and molecules Atoms and molecules are in constant motion – therefore they have kinetic energy Atoms and molecules are arranged differently in different objects – therefore they have potential energy

Thermal Energy Total PE and KE of particles in a substance = thermal energy Example Melting ice cream Fast moving particles in warm air, make the particles in the ice cream move faster, as the kinetic energy of the ice cream particles increases, the thermal energy increases. The ice cream melts.

The energy of electric charges Electrical energy The energy of electric charges Depending on whether the charges are stored or moving, EE can be kinetic or potential.

Almost everything is made up of chemical compounds Chemical Energy Almost everything is made up of chemical compounds Chemical compounds are made up of atoms and molecules Bonds between the atoms and molecules hold the compounds together These chemical bonds have energy

Chemical Energy CE is the energy stored within the chemical bonds of substances. Food we eat Matches Cells in our body When bonds break, chemical energy is released and new compounds may form

Nuclear Energy A type of potential energy Stored in the nucleus of an atom Released during a nuclear reaction Nuclear fission – occurs when a nucleus of an atom is split Used in nuclear power plants

Nuclear Energy Nuclear fusion – occurs when the nuclei of atoms join together Occur continuously in the sun, release tremendous amounts of energy

Electromagnetic Energy Sunlight is a form of Electromagnetic energy Travels in waves EM waves have both electrical and magnetic properties Examples Microwaves X-rays UV radiation Infrared radiation Radio waves

5.3 Energy Transformation and Conservation Niagara Falls A center for a network of electrical power lines Water above the falls is used to generate electricity.

Energy Transformations The mechanical energy of moving water can be transformed into electrical energy. Most forms of energy can be transformed into other forms of energy. A change from one for of energy to another is called: energy transformation

Single Transformations

Multiple Transformations Often a series of transformations are needed to do work A match Mechanical - Thermal - Chemical - Thermal - Electromagnetic The ME used to strike the match is transformed into TE. TE causes the particles in the match to release stored chemical energy, which is transformed into TE and the EME seen as light.

Multiple Transformations A car engine EE produces a spark- TE of spark -> releases CE in fuel - CE turns into TE - TE converted into ME & EE

Transformations between Potential and Kinetic Energy Transformation between Potential energy and Kinetic energy is the most common form of transformation. Any object that rises and falls experiences a change in its kinetic and gravitational potential energy.

Energy transformation in juggling No motion at its highest point, no KE, maximum PE Decreasing KE as it rises PE decreasing, Rising KE In motion = KE High KE No motion = no KE, ball has PE

Energy transformation in a pendulum Pendulum continuously transforms energy from kinetic to potential and back.

Conservation of Energy The law of conservation of energy states: When one form of energy is transformed to another, no energy is destroyed in the process. Energy cannot be created or destroyed The total amount energy is the same before and after any transformation. If you add up all the new forms of energy after a transformation, all the original energy will be accounted for.

Energy and friction Scenario: If you set a spinning top in motion, will it stay in motion forever? WHY? As the top spins, in encounters friction with the surface it is spinning on and with the air. Whenever a moving object experiences friction, some of the KE is transformed into TE. The fact that friction transforms mechanical energy into thermal energy explains why no machine is 100% efficient. Output work is always less than input work in a real machine.

Energy and matter Albert Einstein’s Theory of Relativity During some nuclear reactions, matter is converted to energy. Einstein showed that energy and mass are equivalent and can be converted into one another. E = mc2 is the equation to calculate the amount of energy that is created when matter is destroyed. Matter = anything that has mass and takes up space

5.4 Energy and Fossil Fuels Earth 400 million years ago Lush green swampy forest Enormous dragon flies Huge cockroaches

Formation of Fossil Fuels Fuel – a material that contains stored potential energy Ex. Gasoline used in cars, propane used in grills Fuels used today were formed hundreds of million of years ago. These fuels include: Coal, petroleum, and natural gas Known as Fossil Fuels

Formation of Fossil Fuels Vast ancient forests were the source of coal When plants and animals died, their remains piled up in thick layers in swamps and marshes Clay and sediment covered their remain Over time, increased pressure and temperature turned their remains into coal

Meaning: fuels do not create energy Fossil fuels store energy Energy from the sun Energy is conserved Meaning: fuels do not create energy Fossil fuels store energy Where did they get the energy from? The sun

Energy from the sun Fossil fuels contain energy that came from the sun The sun is the source of energy for most of Earth’s processes Within the dense core of the sun – the process of nuclear fusion –> nuclear energy is transformed into electromagnetic energy as well as other forms. Some of this electromagnetic energy reaches the Earth as light.

The Sun’s energy on Earth When the sun’s energy reaches earth Plants, algae, and certain bacteria - transform some of the light into chemical energy Some of the energy in the chemical compounds they make is used for their daily needs. The rest is stored.

The Sun’s energy on Earth Animals eat plants – store some of the plants chemical energy in their cells When the animals and plants died – some of the energy stored is trapped within them This trapped energy is the chemical energy found in coal.

Burning fuels is known as combustion Use of Fossil Fuels Fossil Fuels can be burned to release the chemical energy stored millions of years ago. Burning fuels is known as combustion During combustion, chemical energy is transformed to thermal energy Thermal energy can heat water to produce steam.

Ex. Modern coal fired power plants: Steam is raised to a high temp in a boiler – leaves the boiler with high pressure – turns a turbine A turbine is a fan connected to an axle – steam causes the blades of the fan to turn very fast – thermal energy is converted to mechanical energy. Turbines are connected to generators that produce electricity. Chemical –> thermal –> mechanical -> electrical

Coal-fired power plants