Unit 3 physics energy
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Unit 3 Physics Energy. Energy. The ability to do WORK… Measured in JOULES (J). Law of Conservation of Energy. energy cannot be created or destroyed only transferred from one form to another. Electric  Light. Chemical  Mechanical. 2 forms of mechanical energy. 1. Kinetic energy (KE)

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Energy
Energy

  • The ability to do WORK…

  • Measured in JOULES (J)


Law of conservation of energy
Law of Conservation of Energy

  • energy cannot be created or destroyed

    only transferred from one form to another

Electric  Light

Chemical  Mechanical


2 forms of mechanical energy
2 forms of mechanical energy

1. Kinetic energy (KE)

-energy due to motion

ex: anything moving

KE = ½ mv2

(J) (kg)(m/s)2

(N) (m)


Calculate ke
Calculate KE

A 1216kg car traveling at 10m/sec.

KE = ½ mv2

m = 1216kg

v = 10m/sec

KE = ½ (1216kg)(10m/sec)2

KE = ½ (1216kg)(100(m/s)2 )

KE = 60,800J


2. Potential energy (PE)

-energy due to position or condition

ex: book high on a shelf

stretched rubber band

wound up clock

-the only PE we calculate is gravitational potential

PE = m g h

(J) (kg)(m/s2)(m)

(N) (m)


Calculate pe
Calculate PE

m =

g =

500N

PE = m g h

h = 100m

PE = (500N) (100m)

PE = 50,000J


Energy1
Energy

7 Types of Energy

  • 1. Light - energy traveling in waves

  • 2. Mechanical - energy of lifting, bending, etc… (work)

  • 3. Thermal - molecular motion


5. Nuclear – energy in atomic nuclei (holds protons & neutrons together)

  • 7. Chemical - energy stored in chemical bonds

4. Electrical – moving electrons

6. Sound - vibrations


Work energy theorem
Work – Energy Theorem neutrons together)

  • All work is energy,

    but not all energy is work


Work neutrons together)

-transfer of energy through motion

*Object must move in direction force applied!


Work neutrons together)

  • Equation: W = Fd

    W = work

    F = force

    d = distance

  • Work is measured in Joules (J)

    J = N m

    *Joule is always (N)(m), never (N)(cm)!!


A teacher pushed a 10kg desk across a floor for a distance of 5m. She exerted a horizontal force of 20N. How much work was done?

F = 20N

d = 5m

W = Fd

W = (20N)(5m)

W = 100J


A force of 10 000n is applied to a stationary wall how much work performed on the wall
A force of 10,000N is applied to a stationary wall. How much work performed on the wall?

F = 10,000N

d = 0m

W = Fd

W = (10,000N)(0m)

W = 0J


Check up
Check up: much work performed on the wall?

  • Where does the pendulum have greatest PE?

  • Where does the pendulum have greatest KE?

Greatest PE

Greatest PE

Greatest KE


Check up1
Check up: much work performed on the wall?

  • Which of the 3 vehicles has the greatest KE?

  • Which car has the greatest KE?


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