work and energy

Work &ENERGY

Energy

• The ability to do work

Work• Using energy to exert a force to

move an object

Work = Energy &

Energy = Work• The work done is equal to the energy

used to do the work.

Calculating Work:

W = 0, if F = 0

W = F d

W = 0, if d = 0

No work done if object doesn’t move.

No work done, whenever there is no force.

Unit: Joule (J) is a Nm

A person pushes with a 110 N force for a distance of 30 m. How much work was done?

Examples:

W = F d

W = ( 110 N ) ( 30 m )

W = 3300 N m

or

W = 3300 J 1 Joule (J) = 1 N m

Potential and Kinetic Energy

Kinetic Energy:

Energy in Motion

Calculating KE:

KE = ½ m v2

KE = 72 J

Example:

What is the KE of 100 kg of water moving at 1.2 m/sec?

KE = 72 ( kg m )/s22

KE = mv2

2

1

KE = ( 100 kg ) ( 1.2 m/s )2

2

1

KE = ( 100 kg ) ( 1.44 m /s )22

2

1

KE = mvKinetic Energy Fact: 2

2

1

The kinetic energy increases dramatically with increasing speed.

35 mi/hr

4 x speed

16 x energy

140 mi/hr70 mi/hr

2 x speed

4 x energy

What is Potential Energy?

oEnergy that is stored and waiting to be used later

What is Potential Energy?

o Potential energy is stored energy

o P.E. = mass x gravity x height

o P.E. = mghDon’t look down,

Rover!Good boy!

Law of Conservation of Energy

• Energy cannot be created or destroyed

• Energy can be transferred from one type or state to another