Unit 4 Lecture Chapter 15

Energy and Work Energy is the ability to do work Energy is measured in Joules (J) Two types: 1. Kinetic- movement 2. Potential- stored

Kinetic Energy Energy in motion Kinetic Energy = ½ x mass x velocity2 KE = ½ mv2 KE is in Joules Mass is in kg Velocity is in m/s

Practice Problems What is the kinetic energy of a jogger with a mass of 65.0 kg traveling at a speed of 3m/s? What is the kinetic energy of a 1 kg pie travelling at a speed of 4 m/s ?

Potential Energy 3 types: 1. Chemical- energy in bonds ex: food, atomic bomb 2. Elastic- energy in things that compress and stretch ex: rubberbands and springs 3. Gravitational- objects suspended above Earth

Gravitational Potential Energy GPE= mass x gravity x height GPE= m x g x h GPE in Joules Mass in kg Gravity on Earth is 9.8 m/s2 Height in m

Practice Problems Find the gravitational potential energy of a light that has a mass of 13.0 kg and is 4.8 m above the ground. A cart at the top of a 300 m hill has a mass of  40 kg.  What is the cart’s gravitational potential energy?

Forms of Energy 1. Mechanical- motion and position, PE + KE 2. Thermal- particles, PE + KE 3. Chemical- chemical bonds and compounds 4. Electrical- electric charges 5. Electromagnetic- the EM Spectrum (radiation spectrum) 6. Nuclear- atomic bonds, atomic decay

Energy Conversions Mechanical Energy = PE + KE (PE + KE)start = (PE + KE)end Meteor falling and impact: KELightHeat Wind up toys: PEKE Lightbulbs: Elec ELight and Heat Food: Chem PEKE + Heat Falling Objects: GPEKE

Energy Conversions in a Pendelum

Law of Conservation of Energy Law of Conservation of energy states: Energy cannot be created or destroyed Energy changes form

Theory of Relativity Energy = mass x speed of light2 E = m x c2 Energy in Joules Mass in kg Speed of light= 3.0 x 108 m/s

Nonrenewable Energy Nonrenewable energy is in limited quantities because it takes millions of years to produce Ex: fossil fuels (coal, oil, natural gas) Ex: elements (Uranium, Plutonium) People have the desire to become more efficient in order to reduce our usage. Ex: energy star appliances, CFL lightbulbs, hybrid cars

Renewable Energy Renewable energy can be replaced in a much shorter time than nonrenewable 4 types: 1. hydro- energy from flowing water ex: falling water turns turbines 2. solar- sunlight heats plates where water flows through, rising steam turns turbines

3. Geothermal- water is pumped into heated underground spaces which creates steam, rising steam turns the turbines 4. Biomass- chemical potential energy is stored in plants, burned or converted into ethanol 5. Wind- turns large turbines