Work, Energy, Kinetic Energy, Potential Energy, and Power

Work

Work is done on an object when energy is transferred to that object

W = Force x distance

Stacking Hay

Energy Work

The capacity to make something happen is Energy

The process of making something happen is Work

Energy and Work have the same unitsKWH, Joules, Ft-Lbs., BTUs, Calorie, K-Calories

Conservation of Energy Energy is not destroyed. Energy is transferred between

objects.(Energy in my body is used to slide a box across the table.)

Energy is converted from one form to another.

(Energy in the box is converted to heat as the table heats up from the sliding box.)

Kinetic Energy

A sliding box is moving, therefore we say it has motion energy or Kinetic Energy.

Other examples of Kinetic Energy:

Moving car

Moving water

Moving wheel

Energy can be stored as Potential Energy

Batteries Gasoline Natural Gas Food Water Towers A wound up alarm clock Toyota Prius battery

IowaWaterQuality.org

http://electronics.howstuffworks.com

http://www.uc.edu

Potential EnergyThe Energy that is stored in an object

Examples:

A stretched rubber band A compressed spring A boulder sitting at the top of a cliff A Roller Coaster ready at the top of the track. A charged battery A voltage source The Human body after eating. Gasoline The Sun

Lego

www.travelblog.org

Steel Dragon 2000 roller coaster in Nagashima, Japan

Gravitational Potential Energy

Gravitational Potential Energy is the energy an object has because of its position relative to the earth.

grav. PE = weight x (height above ground)

http://pinker.wjh.harvard.edu/

Glen Canyon Dam in Utahuses the potential energy of the Colorado River water to produce more thana 1200 MegaWatts or power.

Types of Potential Energy

A stretched rubber band (elastic potential energy) A compressed spring (elastic potential energy) A boulder sitting at the top of a cliff (gravitatoinal potential energy) A Roller Coaster ready at the top of the track. (gravitational

potential energy) A charged battery (chemical potential energy) A voltage source (electric potential energy per unit of charge) The Human body after eating. (chemical potential energy) Gasoline (chemical potential energy) The future light and heat from the Sun (nuclear potential energy) A Dam (gravitational potential energy)

Energy can be stored as Kinetic Energy

(Energy of Motion) Toy car Flywheels A moving car Flying Airplane Earth, planets, the sun, the galaxies Potters Wheels Bicycle Wheels Flywheel Energy Storage (FES) Fast Moving Roller Coasters at the bottom

of the track

Potential Energy Kinetic Energy

Grav. PE Kinetic EnergyWeight x h ½ mv2

A good explanation on Roller Coasters:http://howthingswork.virginia.edu/page1.php?QNum=1319

Animation of Energy Transfer on a Roller Coaster:http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/energy/ce.html

Flywheels

Engine Flywheels help smooth out the rotation of the shaft when a fluctuating torque is exerted on it by its pistons and cylinders.

http://www.craftsmanshipmuseum.com

Kinetic Energy ½ m v2 (translational or linear KE)

m is mass, and v is velocity/speedmass is how much matter is in the objectweight = mass x gravity

½ I 2 (rotational KE)

I is the moment of inertia, or resistance to rotation, and is rotational speed

Inertia is the resistance to a change in motion.More massive objects have greater inertia.

I is the rotational equivalent of mass

is the angular speed expressed as revolutions per minute

The moment of inertia of an object describes how difficult it is to change its angular motion about its axis.

For example, consider two discs (A and B) of the same mass but Disc A has a larger radius than disc B.

Assuming that there is uniform thickness and mass distribution, it requires more effort to rotate disc A (change its angular velocity) because its mass is distributed farther from its axis of rotation: mass that is farther out from the axis must move more quickly than mass closer in.

In this case, disc A has a larger moment of inertia than disc B.

http://en.wikipedia.org/wiki/Moment_of_inertiahttp://www.bsharp.org/physics/stuff/skater.html good video clips of skaters

Storing Energy as Kinetic Energy

Get something massive and accelerate it so that it is moving fast. Due to its mass it will resist slowing down. Massive objects in motion store a lot of Kinetic Energy.

This is why high speed car crashes without restraint devices are often fatal. The energy has to go somewhere and if that energy is not transferred to the seatbelt then the energy will be transferred to other things, like the windshield, the pavement etc.

Consider the toy car:

1. Take the car apart.2. Sketch its gear box3. Determine the torque reduction from the wheels to

the flywheel4. From the flywheel to the wheels, is this speed

reduction or torque reduction?5. Do the wheels have more torque than the flywheel?

How much more?6. How would you redesign the car to climb steep

ramps?7. What might be some limitations to your redesign?

Power

Power = Work/time Units for Power are:

Watts, Horsepower, foot-lbs/minute, BTU/hour