Transcript Work/Energy

• The measure of the ability to do work
• Conservation of energy
-energy can change forms but can not be
-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
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
Velocity 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
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
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.
KE or work being done is = ? Joules
• Potential energy problems --mgh, Joules
3) mass = 10kg., height = 5 meters
PE or Work it can do is = ? Joules
Energy/ Work Problem F X D, Joules (Newton
4) Force = 30 Newtons, Distance = 5 meters
Work or Energy = ? Joules
5) Mass = 10kg., distance = 10meters
Work or Energy = ? Joules
• 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
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 = ?
(.5) x (2) x (100) = 100Joules, North
(4kg) x (2/1 = 22 = 4) x (.5) = 8Joules, down
(10) x (9.8) x (5) = 490Joules
(30) x (5) x = 150Joules
(10kg.) x (9.8) x (10) = 980Joules
6) 150/50 = 3Watts
7) (20Newtons)x(.5meters)/3600sec.=.0028Watts
60sec. In a min.X 60min. In an hour = 3600sec.