THE ABILITY TO DO WORK 1

Energy Energy helps us do things. It gives us light. It warms our bodies and homes. It bakes cakes and keeps milk cold. It runs our TVs and our cars. It makes us grow and move and think. Energy is the power to change things. It is the ability to do work.

Types of Energy Thermal Energy (heat) – The internal motion of particles of matter are called heat energy The faster the particles move, the more heat energy is present. Rub your hands together. You converted mechanical energy (rubbing hands) to heat energy!

Types of Energy Electric Energy - the energy of moving electrons. Power lines carry moving electrical charges that enter homes, schools, and businesses as electricity. Electric motors found in common appliances and machines are driven by electric energy.

Types of Energy Chemical Energy - The energy that bonds atoms together When bonds are broken, stored chemical energy is released. Rocket fuel, Gas Barbeque Throw a ball, you use chemical energy stored in your muscle cells. Food is a source of chemical energy.

Types of Energy Nuclear Energy - The energy stored in the nucleus of an atom. Nuclear fission: when a nucleus splits, nuclear energy is converted to massive amounts of heat and light energy. Nuclear Fusion: nuclei of light elements collide at high speeds and combine, releasing energy: E = mc 2

Types of Energy Electromagnetic Energy – Non- mechanical energy that can travel through space. Possesses wave and particle characteristics. Light: each color of light represents a different amount of electromagnetic energy. Other examples: X-rays, radio waves, ultra violet rays, and infra-red light.

Energy Potential Energy: Stored Energy that is “waiting to be used.” Kinetic Energy: Energy of MOTION

Mechanical Energy The sum of the Kinetic and Potential energies in a system The motion of many objects contain a combination of kinetic and potential energies. ME= KE + PE

Forms of potential energy -position above the Earth ’ s surface -stored in something stretchy -stored in chemical bonds 8

Gravitational Potential Energy An object can store energy as the result of its position.An object can store energy as the result of its position.

Gravitational Potential Energy GPE is the energy stored in an object as the result of its vertical position (i.e., height). Amt. of GPE is dependent on two variables: 1.the mass 2.the height 9

Calculating Gravitational Potential Energy 10

Elastic Potential Elastic PE is the energy stored in elastic materials as the result of their stretching or compressing.

Kinetic Energy Energy of motion. Kinetic energy is "energy that is being used” Heat energy, moving energy, or electrical energy are all forms of energy that are kinetic.

Kinetic Energy KE of an object depends upon two variables: 1.the mass (m) of the object 2.the speed (v) of the object. 5

A formula to find the kinetic energy of any body based on its velocity. Calculating Kinetic Energy 6

12 Conservation of Energy

Conservation of EnergyEnergy cannot be created or destroyed…only changed from one form to another. The total energy of a system remains constant 13

14 ENERGY BEFORE = ENERGY AFTER Energy can be changed from one form to another, but it does not disappear.

TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME Conservation of Energy 1616

Conservation of Energy TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME 1717

Conservation of Mechanical Energy: Therefore, ME i = ME f KE i + PE i = KE f + PE f ½ mv i 2 + mgh i = ½ mv f 2 + mgh f 1818

Energy Conversion When one type of energy is changed or transformed into another type of energy 20

Energy Conversion clip 22

What about a falling object? What happens when it hits the ground? Where did the energy all go? 23

As it is falling and when the object hits the ground the energy is converted into other types of energy such as: Energy Conversions of a dropped object If the object bounces, some energy is converted momentarily into elastic potential energy. sound energy (waves), Light Energy (sparks), thermal energy due to friction (heat) in the ground and air, vibrations in the earth (energy waves.) 24

Questions Questions Which statement about energy is true? A Energy can be increased in a closed system. B Energy cannot be conserved. C Energy can be decreased in a closed system. D Energy cannot be created nor destroyed.

1 minute summary Partner up

Mechanical Energy Practice

Wrap Up Indentify Similarities and Differences 1.Chemical – Nuclear 2.Thermal – Electrical 3.Kinetic – Potential 4.Gravitational – Elastic

Homework Due at the beginning of next class