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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 = 1/2mv2
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
– KE = 8000J
KE = (½)(1000)(10)2
– 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:
PEg = 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 0.655 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 = mc2
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