Chapter 9 Energy

The Big Idea Energy can change from one form to another without a net loss or gain.

Discussion What is energy? Pros and cons? How many different forms of energy can you think of? Take 1 minute with an elbow partner and write down as many things you know about energy

Energy may be the most familiar concept in science, yet it is one of the most difficult to define. Persons, places, and things have energy, but we observe only the effects of energy when something is happening. Only when energy is being transferred from one place to another or transformed from one form to another.

Work! work = net force X distance When you apply a force on an object and it moves, you’ve done work.

Units of Work Remember Work = Force x Distance. What are the units for work? Newton x meters 1 Nm = 1 Joule (J)

Power Power equals the amount of work done divided by the time interval during which the work is done.

Units for Power Remember Work is measured in Joules Power is measured in Joules per Second

Mechanical Energy The energy due to the position of something Or the movement of something. The two forms of mechanical energy are kinetic energy and potential energy.

Potential Energy 3 kinds Elastic Potential Energy Chemical Energy A stretched or compressed spring A stretched rubber band A bow in a bow and arrow Chemical Energy Is released when a chemical change takes place. Gravitational Potential Energy Energy of position in a gravitational field.

Gravitational Potential Energy Focus on this type of potential energy. gravitational potential energy = weight X height Or PE=mgh

Kinetic Energy Energy of motion Or Kinetic energy = 1/2 mass X velocity squared Or

Total Mechanical Energy the total Mechanical energy Add the Kinetic and potential energy ME = KE + PE Let’s think about the units.

Try it. An object has a mass of 10kg. It is 5m off the ground. It is moving 2m/sec. Find its gravitational potential energy. Find its kinetic energy Find its total mechanical energy

Simple Machines A machine transfers energy from one place to another or transforms it from one form to another. A lever is a simple machine made of a bar that turns about a fixed point. The fulcrum is the fixed point that a lever operates on.

Mechanical Advantage. work input = work output The ratio of output force to input force for a machine is called the mechanical advantage.

Try it! Find the mechanical advantage.

Conservation of Energy Energy can neither be created nor destroyed, it is only changed from one form to another.

Work Energy Theorem Anytime Work is done energy changes. We are going to think of this in terms of kinetic energy. Work = KE (Kinetic Energy)