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## PowerPoint Slideshow about 'Unit 3 Physics Energy' - milica

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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)

-energy due to motion

ex: anything moving

KE = ½ mv2

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

(N) (m)

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)

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

- 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?

F = 10,000N

d = 0m

W = Fd

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

W = 0J

Check up:

- Where does the pendulum have greatest PE?
- Where does the pendulum have greatest KE?

Greatest PE

Greatest PE

Greatest KE

Check up:

- Which of the 3 vehicles has the greatest KE?
- Which car has the greatest KE?

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