- Slides: 58
Forms of Energy – Part II
Forms of Energy Mechanical Electrical Chemical Nuclear Thermal/Geother mal Sound Seismic Radiant
Kinetic and Potential Energies Combined Mechanical Energy – The sum of potential energy and kinetic energy in a system of objects. The energy an object has because of a combination of the following: 1. The movement of its parts (kinetic energy) 2. The position of its parts (potential energy) Example: Opening a door • Potential Energy – the energy stored in the person • Kinetic Energy – lifting my hand to push the door • Mechanical Energy – my PE and KE were transferred into mechanical energy which caused work to be done (the door opens).
Mechanical Energy How could a bowling ball have mechanical energy? • PE – bowling ball has mass and the PE increases as you pull it back. • KE – release the bowling ball as it moves down the lane. Because of its mechanical energy it is able to do work on the pins! Can you give some examples of mechanical energy?
Thermal Energy – The sum of the kinetic energy and potential energy of the particles that make up an object Cannot always be seen. Individual particles vibrate back and forth in place, giving them. kinetic energy potential energy The particles also have because of the between particles and distance charge the of the particles.
Thermal Energy As the water heats up to make a cup of coffee the particles begin to increase kinetic energy (velocity of particles) and increase potential energy (distance between particles increases) resulting in an increase of thermal energy.
Thermal Energy in the Earth The particles in Earth’s interior contain great amounts of thermal energy. geothermal This type of energy is called energy Hot rocks underground heat water to produce steam. We drill holes down to the hot region, steam comes up, is purified and used to drive turbines, which drive electric generators.
Geothermal Energy Advantages Does not produce any pollution Power stations do not take up much room, therefore there is not much environmental impact No fuel is needed Once you've built a geothermal power station, the energy is almost free. (It may need a little energy to run a pump, but this can be taken from the energy being generated. ) IF IT’S SO GREAT, WHY DON’T WE USE IT!? • There aren’t many places you can build a power station • You need specific rocks that can be drilled into and at a dep can drill down to.
Types of Kinetic Energy At this point you know that anything in motion has kinetic energy, including: Large objects that you can see Small particles that you cannot see (molecules, ions, atoms, and electrons)
Electric Energy – The energy caused by the movement of electrons. Can be easily transported through power lines and transformed into other forms of energy. Electrons move around the nucleus of an atom and they can move from one atom to another. When electrons move, they have kinetic energy and create an electric current.
Types of Potential Energy Potential energy – stored energy that depends on: Position or shape of an object. Chemical Energy – energy that is stored in and released from the bonds between atoms. petroleum, natural gas, and Most electric energy (a type of kinetic) comes coal. from fossil fuels such as chemical bonds The atoms that make up fossil fuels are joined
Chemical Energy chemical bonds When fossil fuels burn, the break apart between atoms that make up the fossil fuel . chemical energy thermal energy. When this happens, transforms into
What are some other forms of Chemical Energy? The chemical energy in food is released while the food is being digested and the molecules of food are broken down into smaller pieces. As the bonds between the atoms of the food break or loosen, new substances are created as a result of the Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons. Batteries can be stored for a long time and still work because the chemical process doesn't start until the electrons flow from the negative to the positive terminals through a circuit. Air activated hand warmers contain various chemicals. As the disposable packet is opened, oxygen crosses the permeable cover and reacts with iron, in the presence of catalyst salt and water. The production of Fe 2 O 3 is an exothermic reaction, generating heat typically between 1 and 10 hours.
Nuclear Energy – energy stored in and released from the nucleus of an atom. the Sun Majority of energy on Earth comes from nuclear fissionrelease nuclear and Nuclear fusion energy. Nuclear Fusion – A process that occurs in the sun which joins the nuclei of atoms and releases large amounts of energy. Nuclear Fission - Nuclear energy plants on Earth break apart the nuclei of certain atoms.
Energy from Waves Wave – a disturbance that carries energy from one place to another. energy Waves move , NOT matter. WAVELENGTH CREST AMPLITUDE TROUGH
Energy from Waves – Sound Energy – the form of energy associated with the vibration or disturbance of matter Some animals emit sound waves to find their prey. For example: Bats – the amount of time it takes sound waves to travel to their prey and echo back tells the bat the location of the prey it’s hunting.
Energy from Waves Seismic Energy – is the energy transferred by waves moving through the ground. tectonic plates Earthquake’s occur when Earth’s shift suddenly position. kinetic energy seismic The of plate movement is waves carried through the ground by travel through interior of Earth. P (primary) Seismic Waves waves – fastest and first to arrive. S Body waves – (secondary) wave slower, and arrives after p wave. travel through Earth’s crust – responsible for damage associated with earthquakes.
How is Seismic Energy Measured? Seismograph – an instrument for measuring seismic waves (earthquakes). Consists of a frame and a mass that can move relative to it. When the ground shakes, the frame vibrates as well while the mass tends not to move due to inertia. The difference in movement between the frame and the mass is amplified and recorded electronically. Measure: Magnitude: size of earthquake Depth: how deep the earthquake is Location: where the earthquake occurred.
Energy from Waves Radiant Energy – the energy carried by electromagnetic waves. Electromagnetic waves – electric force (example: shock you get when you touch a metal doorknob) and magnetic force (example: the pull that attracts metals to magnets) that move perpendicular to each other to bring on an electric field around them. Can travel through solids, liquids, gasses and vacuums. There are several different kinds of electromagnetic waves – each with different wavelengths, properties, frequencies and power. The entire wave system is called” the electromagnetic spectrum.
Electromagnetic spectrum – the range of all possible frequencies of electromagnetic radiation. The relationship between energy and wavelength: shorter greater The the wavelength the energy. longer weaker The the wavelength the energy. gamma rays The wave with the highest frequency is: radio rays The wave with the lowest frequency is:
What’s the difference? What is the difference between an energy TRANSFER and an energy TRANSFORMATION? When energy moves from one Energy Transfer – object to another without changing its form When one form of energy is Energy Transformation - converted to another form of energy.
Energy Transfers and Transformations In every energy transfer and transformation some energy is transformed into thermal energy. In every transformation such as electric to sound there is always thermal energy being transferred to surroundings.
Transfer or Transformation? Transferred Energy 1. A tennis racket applies force to a tennis ball when it hits the ball, forcing the ball to move forward. 2. A softball player throws a ball toward first base. 3. Fuel in an engine burns, and the car moves forward. 4. A runner eats an energy bar and later that day runs in the 100 -m race. Transformed Energy Type(s) of Energy Being Transferred or Transformed
Transfer or Transformation? 5. Lights glow in the night sky when the power switch is turned on. 6. A hockey stick stops a sliding puck and sends it toward the goal. 7. A truck roars by a row of apartments on a quiet evening. 8. A song plays on the radio.
Plants and The Body Plants carry out a process photosynthesi called s How is photosynthesis an energy transformation? Plants use radiant energy (light from Sun) to transform water and CO 2 into Sugar and Oxygen. Sugar is used as food for the plant and the oxygen is released into the air we breathe.
Types of Kinetic Types of Potential Both Kinetic and Potential
Energy and Work – the transfer of energy that occurs when a force makes an object move in the direction of the force. Force- push or pull on an object For example: The student does work on the drums when he lifts them. Once the drums are in place, no work is being done. With your partners a your table you have minute to come up with 3 examples of work using this definition.
What’s Work? 1. A scientist delivers a speech to an audience of his peers. NO 2. A body builder lifts 350 pounds above his head. YES 3. A mother carries her baby from room to room. NO 4. A father pushes a baby in a carriage. YES 5. A woman carries a 20 kg grocery bag to her car? NO Lets take a closer look at #3 and #5. Think about the definition – why two examples NOT considered work? #3 – the force is applied upward to hold the baby, however the baby moves in a h position with its mother. Therefore the mother is NOT doing work upon the baby. #5 – the force is applied upward to the grocery bag, however the grocery bag mov horizontal position with the woman. Therefore the woman is NOT doing work on
Work is done only while the force is moving the object (in the direction that the force is being applied). Work also depends on: The distance an object moves during the time the force is applied. Joules – the unit of energy and work *Named After: James Prescott Joule – conducted experiments measuring the amount of work needed to create a given amount of heat.
Calculating Work = Force x distance Work Abbreviati Unit on W J (Joules) = 1 kg x m 2/s 2 Force F Distanc d e N (Newtons) = 1 kg x m/s 2 m (meters) = m
Sample Problem 1 A student lifts a bag from the floor to his shoulder 1. 2 meters above the floor, using a force of 50 N. How much work does the student do on the bag?
Sample Problem 2 Nicole lifts a flower pot onto a shelf 3 meters high, using a force of 30 N. How much work is done to place the flower pot onto the shelf?
POWER Power is the rate at which work is done. Power = Work/Time The unit of power is the watt. Watt – equivalent to 1 Joule (work) per second (time)
Check for Understanding 1. Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over head (approximately. 60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds. Which student does the most work? Which student delivers the most Explain your answers. power?
• • Ben and Bonnie do the same amount of work; they apply the same force to lift the same barbell the same distance above their heads. Yet, Ben is the most powerful since he does the same work in less time. Power and time are inversely proportional.
2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s 2 a distance of 10 meters in 5 seconds? This problem requires you to use the formulas force, work, and power all in the correct order. Force=Mass x Acceleration Work=Force x Distance Power = Work/Time
2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s 2 a distance of 10 meters in 5 seconds? This problem requires you to use the formulas force, work, and power all in the correct order. Force=Mass x Acceleration Force=10 x 2 Force=20 N Work=Force x Distance Work = 20 x 10 Work = 200 Joules Power = Work/Time Power = 200/5 Power = 40 watts
Energy and Heat In every energy transformation and every energy transfer, some energy is transformed into thermal energy. Thermal energy – the sum of kinetic and potential energy of the particles that make up an object. (Example: Friction) When thermal energy is moving from a region of higher temperature to a region of lower temperature it is called heat. waste energy it is not easily used to do useful Scientists sometimes call this heat work. because
Machines transfermechanical energy Simple Machines – machines that do work using one movement. Simple machines do not change the amount of work required to do a task; they way work is done only change the
Simple Machines Inclined plane- a flat, sloped surface that makes it easier to move an object from a lower to a higher elevation. . Screw – a modified version of an inclined plane. The threads of the screw are a type of circular ramp (inclined plane)
Simple Machines Wedge – a modified inclined plane. Used to separate or hold devices. Lever – a simple machine that pivots around a fixed point (fulcrum).
Simple Machines Wheel and Axle – a shaft attached to a wheel of a larger diameter so that both rotate together. Pulley – a grooved wheel with a rope or cable wrapped around it.
Machines and Work input work. The work you do on a machine is called the The work the machine does on an object is the output work. Machines make work easier by changing the distance the object moves or the force required to do work on an object *remember – work is the product of force and distance.
Complex Machines – two or more simple machines working together.
Efficiency - the ratio of output work to input work. Efficiency is a measure of how much work put into the machine is changed into useful output work We express efficiency by using a percentage. Efficiency equation:
Efficiency NEVER 100% The efficiency of a machine is Some work is always transformed into wasted thermal energy because offriction How could we improve efficiency of a machine? Reduce the wasted thermal energy by reducing friction. We cou reduce friction by oiling the different parts of the machine.
A light bulb uses 120 J of electrical energy and produces 48 J of light energy. Calculate the percent efficiency of the light bulb.
Calculate the percent efficiency of an electric motor that uses 15, 000 J of energy to produce 11, 500 J of useful energy
Calculate the percent efficiency of an incandescent light bulb that produces 2, 500 J of light energy from 50, 000 J of electrical energy.
Practice Questions 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. 2. How much work is done in pushing an object 7. 0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? 3. Using a single fixed pulley, how heavy a load could you lift?
Practice Questions 4. Give an example of a machine in which friction is both an advantage and a disadvantage. 5. Why is it not possible to have a machine with 100% efficiency? 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input.
Practice Questions 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work. 2. How much work is done in pushing an object 7. 0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W 3. Using a single fixed pulley, how heavy a load could you lift? Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.
Practice Questions 4. Give an example of a machine in which friction is both an advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency. 5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient. 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.
Newton’s Laws and Simple Machines Recall and define each of Newton’s Laws of Motion st 1 Law – an object in motion will stay in motion and an object at rest will stay at rest unless acted on by an unbalanced nd Law – the acceleration of an object is equal to the object’s 2 force. net force divided by the objects mass. 3 rd Law – every action has an equal and opposite reaction. How could we relate these laws to machines?
Newton’s 1 st Law and Machines Newton’s 1 st Law tells us that the motion of an object unbalanced. changes when the forces that act on the object are When you pull a hammer handle, the claws of the hammer apply a force on the nail. The hammer is acting as an unbalanced force that causes the nail to go from to . rest motion
Newton’s 2 nd Law of Motion Newton’s 2 nd Law gives us the relationship between force, mass and acceleration Again, using the hammer as a lever applies to Newton’s 2 nd force Law because the more you apply to the hammer to remove the nail the quicker the nail will out move (accelerate) of the piece of wood.
Newton’s 3 rd Law of Motion Newton’s 3 rd Law says that if one object applies a force on a second object, the second object will apply an equal force in the opposite direction. For example, when you have a hammer being used as a lever to pull out a nail, you apply force on the hammer. The an equal force in the opposite direction (back on you). hammer applies action-reaction force This is an