1. * I. Energy and Work A. Work B. Simple Machines C. Energy
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Ch. 12 – Energy & Work
I. Energy and Work
A. Work
B. Simple Machines
C. Energy *

2. W = Fd A. Work Work transfer of energy through motion*
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A. Work
Work
transfer of energy through motion
force exerted through a distance
W = Fd
W: work (J)
F: force (N)
d: distance (m)
1 J = 1 N·m
Distance must be in direction of force! *

3. *
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A. Work
Brett’s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back?
GIVEN:
F = 30 N
d = 1.5 m
W = ?
WORK:
W = F·d
W = (30 N)(1.5 m)
W = 45 J F W d *

4. d A. Work W F GIVEN: m = 40 kg d = 1.4 m - during d = 2.2 m - after*
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A. Work
A dancer lifts a 40 kg ballerina 1.4 m in the air and walks forward 2.2 m. How much work is done on the ballerina during and after the lift?
GIVEN:
m = 40 kg
d = 1.4 m - during
d = 2.2 m - after
W = ?
WORK:
W = F·d F = m·a
F =(40kg)(9.8m/s2)=392 N
W = (392 N)(1.4 m)
W = 549 J during lift
No work after lift. “d” is not in the direction of the force. F W d *

5. *
B. Simple Machines
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A machine that does work with only one movement is a simple machine.
Lever – bar that is free to pivot about a fixed point called a fulcrum.
Effort arm is part of the lever on which effort force is applied.
Resistance arm is part of the lever that exerts the resistance force.
Three classes of levers based on positions of effort force, resistance force, and fulcrum. *

6. *
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B. Simple Machines
First-class lever – fulcrum is located between the effort and resistance force; multiplies and changes direction of force.
Second-class lever – resistance force is located between the effort and fulcrum; always multiplies force.
Third-class lever – effort force is between the resistance force and fulcrum; doesn’t multiply force but does increase distance over which force is applied *

7. *
B. Simple Machines
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Grooved wheel with a rope, simple chain, or cable running along the groove is a pulley, which is a modified first-class lever.
A fixed pulley is attached to something that doesn’t move; force is not multiplied but direction is changed
A movable pulley has one end of the rope fixed and the wheel free to move; multiplies force
Block and tackle – system of pulleys consisting of fixed and movable pulleys *

8. *
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B. Simple Machines
Wheel and axle – machine with two wheels of different sizes rotating together; modified lever form
Gears are a modified form of the wheel and axle *

9. *
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B. Simple Machines
Inclined Plane – sloping surface that reduces the amount of force required to do work
Less force is required if a ramp is longer and less steep. *

10. *
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B. Simple Machines
Screw – inclined plane wrapped in a spiral around a cylindrical post.
Inclined plane with one or more sloping sides is a wedge.
Compound machine – uses a combination of two or more simple machines. *

11. C. Energy ENERGY THERMAL The ability to cause change. MECHANICAL*
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C. Energy
THERMAL
The ability to cause change.
internal motion of particles
ENERGY
MECHANICAL
NUCLEAR
motion of objects
changes in the nucleus
ELECTRICAL
joules (J)
CHEMICAL
motion of electric charges
bonding of atoms *

12. C. Energy Kinetic Energy (KE) energy in the form of motion*
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C. Energy
Kinetic Energy (KE)
energy in the form of motion
depends on mass and velocity
80 km/h
50 km/h
Which has the most KE?
Which has the least KE?
80 km/h truck
50 km/h motorcycle *

13. C. Energy Potential Energy (PE) stored energy*
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C. Energy
Potential Energy (PE)
stored energy
depends on position or configuration of an object
Which boulder has greater gravitational PE?
What other ways can an object store energy? *

14. C. Conservation of Energy*
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C. Conservation of Energy
Law of Conservation of Energy
Energy may change forms, but it cannot be created or destroyed under ordinary conditions.
EX:
PE  KE
mechanical  thermal
chemical  thermal *

15. C. Conservation of Energy*
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C. Conservation of Energy
PE  KE
View pendulum animation.
View roller coaster animation. *

16. C. Conservation of Energy*
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C. Conservation of Energy
Mechanical  Thermal
View rolling ball animations.
View skier animation. *