Warm-Up: How much power is required to lift a 50N box 3 m in 5 s? A box has a mass of 5kg. What is its weight? Describe in your own words what power is. (USE SCIENTIFIC DEFINITION)

Warm-Up: What is the equation for power? A box has a mass of 5kg. What is its weight? Describe in your own words what power is. (USE SCIENTIFIC DEFINITION)

Work and Energy: Forms and Changes

Energy The ability to do work It is like the “Currency” for performing work. To do 100 J of work, you must expend 100 J of energy Energy

Energy Energy is all around you: You use energy when you: Light Heat Wind You use energy when you: hit a softball lift your book bag digest food Every change that occurs—large or small—involves energy

Changes Require Energy When something is able to change its environment or itself, it has energy Anything that causes change must have energy You use energy to arrange your hair to look the way you want it to You also use energy when you walk down the halls of your school between classes or eat your lunch

Nature of Energy What is energy? Energy- the ability to do work If an object or organism does work the object or organism uses energy Whenever you do work you transfer energy from one thing to another

Nature of Energy Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J) In addition to using energy to do work, objects gain energy because work is being done on them

ANSWER QUESTION 9 ON YOUR CATAPULT WS IN YOUR OWN WORDS ANSWER QUESTION 9 ON YOUR CATAPULT WS

Forms of Energy Some examples of different forms of energy are: Thermal (heat) Chemical Electromagnetic Nuclear Mechanical If you have $100, you could store it in a variety of forms—cash in your wallet, a bank account, or coins Regardless of its form, money is money, and the same goes for energy in that these are only different forms of the same thing

States of Energy The most common energy conversion is the conversion between potential and kinetic energy All forms of energy can be in either of two states: Potential Kinetic

Kinetic Energy Kinetic energy- the energy of motion Depends on both mass and velocity The faster an object moves, the more kinetic energy it has The greater the mass of a moving object, the more kinetic energy it has KE = Ek = mass x velocity2 2 What has a greater effect on kinetic energy, mass or velocity? Why?

Potential Energy Even motionless objects have energy Potential energy- stored energy due to interactions between objects If the apple stays in the tree, the energy will remain stored If the apple falls, that stored energy is converted to kinetic energy

When did you use PE? Explain how your catapult utilized PE.

When did you use KE? Explain how your catapult utilized KE.

Common forms of Potential Energy You will each be given one of three common forms of PE. Read your slide of information and write a 1 sentence summary in your notebook. Share your 1-sentence summaries with other classmates. You should write down their 1-sentence summary in your notes. You need one for: Elastic PE; Chemical PE; and Gravitational PE

Elastic Potential Energy If you stretch a rubber band and let it go, it sails across the room As it flies through the air, it has kinetic energy due to its motion but where did this kinetic energy come from? The stretched rubber band had energy stored as elastic potential energy Elastic potential energy is energy stored by something that can stretch or compress, such as a rubber band or spring

Chemical Potential Energy Gasoline, food, and other substances have chemical potential energy Energy stored due to chemical bonds is chemical potential energy Energy is stored due to the bonds that hold the atoms together and is released when the gas is burned

Gravitational Potential Energy Any system that has objects that are attracted to each other through gravity has gravitational potential energy Gravitational potential energy (GPE) - energy due to gravitational forces between objects Water and Earth Apple and Earth

Gravitational Potential Energy Depends on mass and height PE = mgh PE = Ep = m (kg) x g (m/s2) x h (m) where g is the force caused by gravity (9.8 m/s2) If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board A person with 3 times a larger mass has 3 times the potential energy

Gravitational Potential Energy A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy

Check for Understanding Ek = 1 mv2 2 What is the kinetic energy of a 100 kg man moving 5 m/s? What is the kinetic energy of 0.5 kg ball moving at 30 m/s?

Check for Understanding Ek = 1 mv2 2 What is the kinetic energy of a 100 kg man moving 5 m/s? 1 mv2 = 1 x 100kg x (5m/s)2 = 1250 J 2 2 What is the kinetic energy of 0.5 kg ball moving at 30 m/s? 1 mv2 = 1 x 0.5kg x (30m/s)2 = 225 J 2 2 Eureka! Kinetic Energy

Check for Understanding Ep = m x g x h A 100 kg boulder is on the edge of the cliff 10 m off the ground. How much energy does it have? A 0.5 kg ball is thrown 15 m into the air How much potential energy does it have at its highest point?

Check for Understanding E = m x g x h A 100 kg boulder is on the edge of the cliff 10 m off the ground. How much energy does it have? 100kg x 9.8 m/s2 x 10m = ~ 10,000 J A 0.5 kg ball is thrown 15 m into the air How much potential energy does it have at its highest point? 0.5 kg x 9.8 m/s2 x 15m = ~ 75 J Eureka! Potential Energy

ANSWER QUESTION 10

The Law of Conservation of Energy The Law of Conservation of Energy- energy can be neither created nor destroyed by ordinary means, it can only be converted from one form to another Energy can change from one form to another, but the total amount of energy never changes The total energy of a system remains constant

Energy Transformations The law of conservation of energy is a universal principle that describes what happens to energy as it is transferred from one object to another or as it is transformed You are likely to think of energy as race cars roar past or as your body uses energy from food to help it move, or as the Sun warms your skin on a summer day These situations involve energy changing from one form to another form

Mechanical Energy Transformations Mechanical energy is the sum of the kinetic energy and potential energy of the objects in a system The mechanical energy of a system remains constant or nearly constant In these cases, energy is only converted between different forms of mechanical energy

Mechanical Energy Transformations An apple-Earth system has gravitational potential energy due to the gravitational force between apple and Earth The instant the apple comes loose from the tree: It accelerates due to gravity It loses height so the gravitational potential energy decreases Its potential energy is transformed into kinetic as the speed of the apple increases The potential energy that the apple lost is gained back as kinetic energy so the total amount of energy remains the same

Energy Transformation in Projectile Motion Energy transformations also occur during projectile motion when an object moves in a curved path However, the mechanical energy of the ball-Earth system remains constant as it rises and falls

Energy Transformation in a Basketball Ball speeds up Ball slows down Force of gravity

Energy Transformation in a Roller Coaster At the point of maximum potential energy, the car has minimum kinetic energy. Total energy is conserved and constant

Energy Transformations in a Swing When you ride on a swing part of the fun is the feeling of almost falling as you drop from the highest point to the lowest point of the swing’s path The ride starts with a push that gets you moving, giving you kinetic energy As the swing rises, you lose speed but gain height In energy terms, kinetic energy changes to gravitational potential energy

The Effect of Friction You know that if you don’t continue to pump a swing or get a push, your arcs will become lower and you eventually will stop swinging In other words, the mechanical (kinetic and potential) energy of the swing decreases, as if the energy were being destroyed or lost Is this a violation of the law of conservation of energy?

The Effect of Friction NO!!! Energy in the system is conserved With every movement, the swing’s chains rub on their hooks and air pushes on the rider Friction and air resistance cause some of the mechanical energy of the swing to change to thermal energy With every pass of the swing, the temperature of the hooks and the air increases a little, so the mechanical energy of the swing is not destroyed, but transformed into thermal energy, or heat

Conservation of Energy with a Pendulum When is the pendulum moving the fastest? at the lowest point

Conservation of Energy with a Pendulum When does the pendulum have the most kinetic energy? at the lowest point

Conservation of Energy with a Pendulum When does the pendulum have the most gravitational potential energy? at the highest point

Conservation of Energy with a Pendulum K E

Conservation of Energy with a Pendulum K E Gravitational potential energy depends on height

Conservation of Energy with a Pendulum K E Kinetic energy depends on speed

E = P + K P K E

Total Energy Doesn’t Change P + K = E

A Pendulum PE PE All KE No KE No KE

Transforming Electrical Energy Light bulbs transform electrical energy into light so you can see The warmth you feel around the bulb is evidence that some of that electrical energy is transformed into thermal energy, or heat

Transforming Chemical Energy Fuel stores chemical potential energy An engine transforms chemical potential energy of gasoline molecules into the kinetic energy of a moving car or bus Several energy conversions occur in this process In a car, a spark plug fires, initiating the conversion of chemical potential energy into thermal energy As the hot gases expand, thermal energy is converted into kinetic energy

Transforming Chemical Energy Some chemical energy transformations are less obvious because they do not result in visible motion, sound, heat or light Every green plant you see converts the radiant energy from the Sun into the energy stored in chemical bonds in the plant, like in carbohydrates (sugars) When we eat we transform the potential energy stored in the carbohydrate bonds and transform it into kinetic energy

Other Energy Conversions In a battery, chemical energy is converted into electromagnetic energy The mechanical energy of a waterfall is converted to electrical energy in a generator Chemical  Thermal Mechanical

Check for Understanding B Where is the gravitational potential energy maximum? Where is the kinetic energy maximum? Where is the gravitational potential energy minimum? Where is the kinetic energy minimum?

Check for Understanding B Where is the gravitational potential energy maximum? A and E Where is the kinetic energy maximum? C Where is the gravitational potential energy minimum? C Where is the kinetic energy minimum? A and E

Exit Ticket Describe in your own words what the difference between KE and PE is.