SP1.Students will analyze the forms and transformations of energy.

Mechanical Energy

Energy Energy is the ability to cause change Anything that changes uses energy Energy is measured in Joules (J), just like work One form of energy is Kinetic energy (KE)

How much KE?

How Much KE?

Kinetic Energy (KE) Moving energy Dependent on –Mass Mass, KE –Velocity Velocity, KE

Kinetic Energy (KE) The equation for KE is KE = 1/2mv 2 KE = 1/2mv 2 Because velocity is squared, the KE will go up very fast as you increase velocity

Example A 1,000kg truck was traveling at 4m/s and then accelerated to 10m/s. Find the initial KE and the final KE. KE = 1/2mv2 KE = (½)(1000)(4)2 –K–K–K–KE = 8000J KE = (½)(1000)(10)2 –K–K–K–KE = 50000J

Potential Energy Potential energy is stored energy It comes in many forms: –Gravitational –Elastic –Chemical –Electric –Etc.

What kind of PE?

Gravitational Potential Energy (GPE) Is the energy an object will use to fall. Depends on the object’s : –Weight (mass * gravity) –Height from ground (or whatever it’s falling to) Equation for GPE: PE g = mgh PE g = mgh

Problem A 0.06 kg tennis ball starts to fall from a height of 2.9m. What was its gravitational potential energy at that height? GPE = mgh GPE = (0.06)(10)(2.9) GPE = 1.74J

Elastic Potential Energy Elastic potential energy comes when an object is stretched or compressed. This depends on how far the object has been distorted.

Mechanical Energy Mechanical energy is the energy of a system Mechanical energy (ME) comes from two different sources: –Potential energy –Kinetic energy Mechanical energy typically does not include nuclear, chemical, electrical and other ancillary types of energy

Conservation of Energy In a system, the mechanical energy is conserved. The amount of energy in the beginning should equal the amount of energy at the end* *minus energy loss due to friction

Converting Energy Mechanical Energy is the total of the potential and kinetic energy in a system. ME = PE + KE

Converting Energy Though GPE and KE change, the total energy remains constant.

Open vs. Closed Systems A closed system is one where no energy is added An open system does add energy

Try It The tops of the towers on the Golden Gate Bridge are 227m above the water. Suppose that a worker drops a kg wrench from the top of the tower. What will be the kinetic energy of the wrench when it hits the water?

Mass and Energy Sometimes, mass can be converted into energy –Ex: Nuclear fission/fusion The equation for the amount of energy produced is E = mc 2

Now it’s your turn! Do the problems on the worksheet

ToD Name three types of energy transformations you’ve used today Show your work