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