Energy

1. Energy

2. What the heck is energy anyway? • Energy- the ability to do work • If an object or organism does work (exerts a force over a distance to move an object) the object or organism uses energy. • Work = force x distance • ex. When stretching a sling shot, you do work, and energy is transferred to the sling shot • Measured in the unit joules • b/c work is a force x distance it is measured in Newtons x meters. These units are called joules. • 1 N x m = 1 J= 1 kg x m2/s2

3. Energy • Living organisms need energy for growth and movement. • You use energy when you hit a tennis ball, compress a spring, or lift a grocery bag. • Energy is the ability to do work

4. Nature of Energy • Energy is all around you! • You can hear energy as sound. • You can see energy as light. • And you can feel it as wind.

5. Nature of Energy Living organisms need energy for growth and movement.

6. Types of Energy • 1. Potential energy- energy that an object has b/c of its position, shape, or condition of the object • Called “energy of position” or “stored energy” • Stretched rubber band has potential energy b/c the 2 ends are far away from each other (elastic potential energy)

7. Gravitational potential energy • Gravitational potential energy- any system of 2 or more objects separated by a distance; results from gravitational attraction b/w the objects • ex. Apple in a tree • Grav. PE = mass x free-fall acc. X height • PE = mgh

8. Gravitational Potential Energy • An apple at the top of the tree has more grav. PE w/ respect to the Earth than a similar apple on a lower branch. • But if two apples of different masses are at the same height, the heavier apple has more grav. PE than the lighter one

9. Types of Energy • 2. Kinetic Energy-energy of a moving object due to the object’s motion -depends on mass & speed Kinetic energy = ½ x mass x speed squared KE = ½ x mv2 • in the KE equation, speed is squared so a small increase in speed produces a large increase in KE ex. Why car crashes are more dangerous at high speeds • Atoms/molecules have KE b/c they are constantly in motion (KE ↑ as particles heat up or KE ↓ as particles cool down)

10. Mechanical vs. Nonmechanical potential energy • A. Mechanical potential energy – energy that you can see on a large scale; you know that it is there b/c of the height ; • Mechanical potential energy exists because of the relative positions of two or more objects. For example, a rock resting on  the  edge  of  a  cliff  in  such  a  position  that  it will   fall   freely   if   pushed   has   mechanical potential energy. • Water at the top of a dam has mechanical potential energy. A sled that is being held  at  the  top  of  an  icy  hill  has  mechanical potential energy.   • B. Non-mechanical potential energy- energy that you CANNOT SEE that is present in chemical bonds • ex. dynamite

11. Mechanical vs. Nonmechanical Kinetic energy • A. Mechanical kinetic energy- Kinetic  energy  exists  because of the relative velocities of two or more objects. • Examples: If you push that rock, open the gate of the dam or  let  go  of  the  sled,  something  will  move. • The rock  will  fall;  the  water  will  flow;  the  sled  will slide down the hill. In each case the mechanical potential  energy  will  be  changed  to  mechanical kinetic energy. Another way of saying this is that the  energy  of  position  will  be  changed  to  the energy  of  motion. This is energy that is clearly visible; an object is moving. • B Non-mechanical kinetic energy –energy that is NOT VISIBLE but you know that it is there b/c it is present in the atoms of a molecule (moving) • ex. Solid, liquid, gas atoms moving (dance moves)

12. Kinetic Energy

13. Types of Energy • 3. Mechanical energy- sum of the potential & kinetic energy in a system • The amount of work an object can do because of the object’s kinetic and potential energies • *** If something has mechanical energy you can see it move (or you would see it move if it only has potential energy) • ex. Apples have potential energy when they are hanging above the ground, & they have kinetic & potential energy when they are falling • ex. Roller coaster

14. Non-mechanical Energy • Energy that lies at the level of atoms and does not affect motion on a large scale • Example: apples give you energy when you eat them • Atoms and molecules are constantly in motion so they have kinetic energy • The kinetic energy is transferred through the particles through collisions • Average kinetic energy of particles in an object increases as the object gets hotter and decreases as it cools down

15. Nonmechanical Energy • ***Nonmechanical energy can be heat energy, light energy (electromagnetic), chemical energy, or nuclear energy. Once again, you CANNOT SEE nonmechanical energy*

16. Can mechanical energy change to non-mechanical energy? • Yes, as a result of air resistance and friction. • Moving an object across another can result in heat through friction. This is conversion of the mechanical energy into thermal energy. • In an electric motor, the (mechanical) rotation of the coils results in electrical current and therefore electrical energy.

17. Types of Energy • 4. Chemical Energy- The amount of chemical energy associated w/ a substance depends in part on the relative positions of the atoms it contains • formation of bonds and the breaking of bonds during chemical reactions • ex. Burning a match • B/c chemical energy depends on position, it is a kind of potential energy

18. Chemical Energy • Energy that exists in the bonds that hold atoms together. • When bonds are broken, chemical energy is released. • Examples: • Digesting food…bonds are broken to release energy for your body to store and use. • Sports… your body uses energy stored in your muscles obtained from food. • Fire–a chemical change.

19. Chemical Energy • Fuel and food are forms of stored chemical energy (potential).

20. Types of Energy • 5. Nuclear Energy- kind of potential energy stored by the forces holding subatomic particles together in the nuclei of atoms • Nuclear Fusion- a type of reaction in which light atomic nuclei combine to form a heavier nucleus • ex. How sun works • Nuclear Fission- a single heavy nucleus is split into 2 or more lighter nuclei

21. Types of Energy • 6. Electricity- results from the flow of charged particles through a wire or other conducting materials • Lightning is caused by electrons traveling through the air b/w the ground & a thundercloud

22. Types of Energy • 7. Electromagnetic Energy (Light)- travels from the sun to the Earth across empty space in the form of electromagnetic waves

23. Electromagnetic Energy • Light is a form of electromagnetic energy. • Each color of light (Roy G Biv) represents a different amount of electromagnetic energy. • Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.

24. Types of Energy • 8. Thermal Energy is the kind of energy that is related to and/or caused by heat. • When you boil a pot of water, you are contributing thermal energy or heat to the bottom of the pot. This thermal energy is then transferred to the water inside the pot. • As the water molecules move faster (kinetic energy), they begin to get hotter. As they move faster and faster, each one tries to leap away from its neighbors and into the surrounding air to form water vapor, or steam. Once the water starts boiling, it turns into steam very quickly!