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