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More NRG

More NRG. Mechanical NRG. Mechanical energy is the total amount of potential and kinetic energy in a system. 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.

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More NRG

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  1. More NRG

  2. Mechanical NRG • Mechanical energy is the total amount of potential and kinetic energy in a system

  3. 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?

  4. Energy Pathway • Energy changes forms but on Earth our energy comes from the sun

  5. 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

  6. 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= Work

  7. 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. Thermal energy

  8. Heat • Heat • The flow of thermal energy from one object to another. • Heat always flows from warmer to cooler objects

  9. 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?

  10. Which object has more thermal energy • SMALL HOT OBJECT • High Temperature but low mass • LARGE COLD OBJECT • Lower Temperature but Large mass

  11. Temperature • Temperature is the measure of thermal energy • There is no such thing as cold • People use temperature relatively

  12. 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 C • C sand = 664 J / kg C

  13. 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 Calculating specific heat

  14. 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 = 20oCq = 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 Formula

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