ENERGY

• The measure of the ability to do work• Conservation of energy

-energy can change forms but can not be destroyed-the total amount of energy in the Universe remains constant!!!!!!!!!!!!!!!!

-matter acts the same way (total amount remains constant)

**Energy is measured in Joules (label, unit)

Potential and Kinetic Energy

• Potential energy of an object

-stored, ready to use energy

-could be because of chemical composition

-could be because of position of the object

-to calculate chemical potential energy of an object --measure the amount of chemicals in the object

The amount of potential energy an object contains is the amount of work the object could do to another object

-to calculate position energy of an object

-measure mass x 9.8m/s2 x height lifted

kilogram x gravity(use 10) x meter

balance scale x constant x meter stick

Kinetic energy of an object

-determined by an object’s motion

-kinetic energy is the work an object is doing on another object

-to calculate motion energy

• ½ x mass x velocity x velocity.5 x kg x (speed and direction)2

meters/secondsVelocity is a vector

-vectors explain magnitude and direction of an object’s motion

-magnitude --how fast-direction --which way

-used to predict where the object will be in the future (graph)

• The potential energy of an object is equal to the kinetic energy or work that it takes to gain that energy

• Then it will have that much potential energy to use• Other examples

1234

Work and Energy

• The label for energy and work is Joule• Joule = Newton x meter

force x distance

-to find distance --measure with a meter stick

-to find force --use a spring scale

-force is an amount of weight

-gravity pulling on mass creates weight

(force)

The word work is interchangeable for the words potential and kinetic energy

• Mass x gravity = force

• Kilogram x 9.8m/s2 = Newton

• For work to be done, the object must move in the direction of the applied force

Problems to do

• Kinetic energy problems -1/2MV2, Joules

1) M = 2kg, V = 10m/s, V = North

KE or work being done = ? Joules

2) Meters = 2, seconds = 1, Mass = 4kg.

down

KE or work being done is = ? Joules

• Potential energy problems --mgh, Joules3) mass = 10kg., height = 5 meters

PE or Work it can do is = ? Joules

Energy/ Work Problem F X D, Joules (Newton Meters)

4) Force = 30 Newtons, Distance = 5 metersWork or Energy = ? Joules

5) Mass = 10kg., distance = 10metersWork or Energy = ? Joules

Power

• Rate of work done• To calculate -work/time (work divided by time)• Work / time

Joule seconds

Newton X meter

force distance

Kilogram X 9.8m/s2

mass X acceleration rate due to gravity

• Power is measured in Watts -label

• Kilowatt hour -how much energy is used in an hour -how electric bill is calculated

• Power Problem –Work/time, Watts

6) Workdone = 150Joules, time =50seconds

Power = ?

7) Force = 20Newtons, distance = .5meters, time = 1 hour (seconds)

Power = ?

Answers

1) (.5) x (2) x (100) = 100Joules, North2) (4kg) x (2/1 = 22 = 4) x (.5) = 8Joules, down3) (10) x (9.8) x (5) = 490Joules4) (30) x (5) x = 150Joules5) (10kg.) x (9.8) x (10) = 980Joules Force6) 150/50 = 3Watts7) (20Newtons)x(.5meters)/3600sec.=.0028Watts

60sec. In a min.X 60min. In an hour = 3600sec.