Date post: | 05-Jan-2016 |
Category: |
Documents |
Upload: | evangeline-paul |
View: | 220 times |
Download: | 0 times |
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: KELightHeat• Wind up toys: PEKE• Lightbulbs: Elec ELight and Heat• Food: Chem PEKE + Heat• Falling Objects: GPEKE
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