ENERGY and Work
What is energy? • Ability to make something happen • Or work to happen
Potential and Kinetic Energy • Potential energy is energy that is stored in an object. • Kinetic energy is energy of motion.
Potential energy • Potential energy (P.E.) is the ability of an object to do work because of its position. work done by the object = P.E. lost • work done on the object = P.E. gained.
Potential energy • Potential energy is a type of energy that is "hidden" in some way. It is a type of energy that can be converted to other forms and often is related to some attractive or pushing forces.
Types • Elastic Potential Energy • Anything that can act like a spring or a rubber band can have elastic potential energy. • Let's take the rubber band or a spring • Wind up toys store energy this way
Gravitational Potential Energy • There is a constant attractive force between the Earth and everything surrounding it, due to gravity. • To lift something off the ground it takes energy, so just by lifting an object, that object now has higher gravitational potential energy.
Gravitational potential energy is typically converted into kinetic energy (an object falling) before it is converted into any other type of energy. • Hydroelectric power is generated this way. As the water falls, it turns a turbine, which pushes electrons around, creating an
Changing GPE • What does it depend on?
Chemical Potential Energy • A chemical bond can be thought of as an attractive force between atoms. • Because of this, atoms and molecules can have chemical potential energy. • Anytime two atoms form a strong covalent or ionic bond or two molecules form a chemical energy is converted into other forms of energy, usually in the form of heat and light.
Strong bonds have low chemical energy and weak bonds have high chemical energy.
Kinetic energy is the energy of motion. • Any object that is moving has kinetic energy. • Ball Moving Horizontally • Kinetic Energy Equation • m = mass (in kg), v = velocity (in m/s), and KE = kinetic energy (in J = joules).
Remember, the units for energy are Joules - Kilogram . meters / sec2
Practice Problems: • 1. A 12 pound bowling ball is held 20 feet above the floor. Calculate its GPE. • 2. A 2kg object is traveling at 4m/s. Calculate its KE.
Law of Conservation of Matter and Energy:the total matter and energy in the universe is always conserved.
Can energy be changed into matter? • Think of matter and energy as two forms of the same thing that can be converted from one to another.
E=mc2 • While it is possible to change matter into energy and energy into matter, the sum of the two is always constant. • Einstein's equation shows this relationship. • E = Energy (Joules) • m = mass (kg) • c = speed of light (300,000 km/s)
The two most common energy conversions are: • Potential energy changing into kinetic energy. • Kinetic energy changing into potential energy
Mechanical energy= potential energy + kinetic energy • Mechanical is energy due to the motion of an object
Forms of energy • Mechanical • Chemical • Heat • Electromagnetic • nuclear
Mechanical energy • There are two main types of mechanical energy. • Motion energy: This is the energy something has because it is moving • Stored mechanical energy: This is energy something has stored in it because of its height above the ground or because it is stretched or bent or squeezed
Electrical energy • The energy that flows through wires and powers the lights and appliances in your home. • The energy is in the form of moving electrons
Electromagnetic energy • Visible light or radiant energy • X rays • Radio waves • Microwaves • This form of energy can travel through a vacuum
Concept Understanding: • 1. Assume that all the matter in your body could be converted into energy, how many Joules of energy would that be? • Hint: 1 pound = 0.5 kg • Show all your work used to solve this problem. • 2. Give one example of each of the following energy conversions: • Chemical energy changing into heat energy. • Heat energy changing into mechanical energy. • Nuclear energy changing into heat energy. • Mechanical energy changing into electromagnetic energy.
Conservation • Matter can be changed into energy • Energy can be changed into matter • Neither can be created or destroyed
Work • Develop a definition from the activity
Work • W=force x distance • W=fxd • The unit is the newton/meter also called joule • Work is force exerted through a distance • Complete activity pg 303
Measure work • To measure work you must measure the force in the direction of motion • Complete problems #3, 7, and 8 on page 303
Power • Power=work/time • It is a rate • The unit is the watt---W or 1 j/s
Analysis and conclusion • 1 When the mass is released from the same height with the interrupter, is the ending height the same as its starting height? Use your data to support
2 Analyze the energy transfers. At what point along a single swing does the mass have the greatest kinetic energy? The greatest potential energy
3 Do the results support your hypothesis? • 4 Compare the starting heights to the ending heights of the mass. Is there a pattern? Can you account for the observed behavior?
5 Do your results support the law of conservation of energy? Why or why not? • 6 What would happen if the mass of the bob was increased?