More NRG

Conservation

• Law of conservation of energy: energy may change form but it cannot be created or destroyed under normal conditions

• Where is a lot of our energy lost?

Energy Pathway• Energy changes

forms but on Earth our energy comes from the sun

Storing energy

• At times we need to store energy

• Energy storage is difficult in large amounts

• Most energy is stored as chemical energy.

• Batteries, food, oil, etc.

Chemical bonds

• The arrangement of bonds of atoms can store large amounts of potential energy.

• The energy in fuels is extracted by rearranging these bonds.

Where do people attain the energy for living?

• Food is chemical potential energy

• 1 kilocalorie or Calorie =4180 J

• Protein = 4 Calories/gram• Carbs = 4 Calories/gram• Fats = 9 Calories/gram • You are eating sunshine

Work

• Work causes a change in something

• Work = force x distance or…

• W= F x d• Work is labeled as

Joules or J

• A rock weighing 50N is lifted 65m by a crane, what is the amount of work being done?

• 50N x 65m=

Thermal energy

• The molecules of all substances - solids, liquids and gasses -- are in motion.  The velocity of the molecule will depend on the temperature and the mass of the molecule, but they are all in motion.

• When two objects are in thermal contact, heat will flow until the two objects are in thermal equilibrium.

• The only way to change the temperature of a body is to add or remove energy.

Heat

• Heat• The flow of thermal

energy from one object to another.

• Heat always flows from warmer to cooler objects

• Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.

• How much energy would have to be removed to reach absolute zero?

Which object has more thermal energy

• SMALL HOT OBJECT

• High Temperature but low mass

• LARGE COLD OBJECT

• Lower Temperature but Large mass

Temperature

• Temperature is the measure of thermal energy

• There is no such thing as cold

• People use temperature relatively

Specific Heat

• Some things heat up or cool down faster than others.

• Specific heat is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C or K).

C water = 4184 J / kg CC sand = 664 J / kg C

Calculating specific heat

• This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

• Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds and do not need as much energy to break them

• How to calculate changes in thermal energy

• Q = m x ΔT x Cp• Q = change in thermal

energy• m = mass of substance• Δ T = change in

temperature (Tf – Ti)• Cp = specific heat of

substance

Formula

• Calculate the amount of heat needed to increase the temperature of 5 kg of water from 20oC to 56oC.

• q = m x C x (Tf - Ti) • m = 5 kg• C = 4184 J oC kg • Tf = 56oC Ti = 20oC

q = 5 x 4184 x (56 - 20)q = 5 x 4184 x 36q = 753120 J

• Knowing its Q value, its mass, and its T, its C can be calculated.

• C = Q/(m x T)• Calculate the specific

heat of copper if 205J will raise the temp. of 15g of copper from 25 to 60

• Q = 205 J• M =15g or .015kg T = 35