Transcript Chapter 14 Work, Power, and Machines

Work
 Work – ________________________________________
 When a force acts on an object in the direction the
object moves.
Work Requires Motion
 For a force to do work on an object, some of the force
must act in _____________________________________
 If there is _________movement, ________work is done
 The weight lifter does no work on the barbell as he
holds it over his head
Work Depends on Direction
 __________________________________________________
__________________________________________________
__________________________________________________
 Any part of a force that does not act in the direction of
motion does no work on an object.
Calculating Work
 The weight lifter did do work when ________________
________________________________________________.
 Units of Work:
 Joule – _________________________________________
 Using the work formula:
Power
 Power – _______________________________________
 Work at a faster rate – ____________________________
 To increase power – _______________________________
__________________________________________________

Or do a given amount of work in less time.
Calculating Power
 The SI unit of power is the
_______________________= 1 joule/second
Horsepower
 _______________________________________________
 James Watt compared ___________________________
________________________________________________
 After many experiments, he defined the horsepower
_______________________________________________
Machine
 _______________________________________________
 Make work easier to do.
 Change the ____________ of a force needed, the
________________of a force, or the
________________over which a force acts
 Increasing Force
 If a machine ______________the distance over which
you exert a force, then it ___________________the
amount of force you need to exert.
 Ex: Raising a car using a jack
 Increasing Distance
 Some machines _____________applied force, but
_______________the distance over which the force is
exerted.
 Increased travel of oar through water =
______________________________________________
 Changing direction
 ________________________________________________
________________________________________________
Work Input
 Work input – ___________________________________
_______________________________________________
 Input force – ____________________________________
 Input distance – _________________________________
Work Output
 Work Output – _________________________________
________________________________________________
 Only way to increase work output is to increase the
amount of work you put __________________________
 Output force – _________________________________
Mechanical Advantage
 _______________________________________________
_______________________________________________
 Actual mechanical advantage (AMA) – ___________
_______________________________________________
 Loading ramp – inclined ramp decreases input force
needed to lift refrigerator into truck.
 Ideal Mechanical Advantage (IMA) ______________
_______________________________________________
 Because friction is always present, the actual mechanical
advantage of a machine is always ______________the
ideal mechanical advantage.
 How can you increase the actual mechanical advantage
of the ramp?
Efficiency
 Some work input always used to __________________
 Work output always ___________________work input
 Efficiency – ____________________________________
_______________________________________________
 Because there is always some friction, the efficiency of a
machine is always less than ________%.
 Reducing friction ________________efficiency of a
machine

Roller bearings lubricated with grease
Six Types of Machines
 The six types of machines are:
1. Lever
2. Wheel and axle
3. Inclined plane
4. Wedge
5. Screw
6. Pulley
Levers
 _______________________________________________
_______________________________________________
 Fulcrum – _______________________________________
________________________________________________
 Screwdriver under paint can lid
Levers
 First-class levers – Fulcrum of first-class lever is always
located _______________the input force and the
output force.
 ______________________
________________________
 Second-class levers – ____________________________
________________________________________________
 Wheelbarrel
 Third-class levers – ______________________________
_______________________________________________
Wheel and Axle
 _______________________________________________
_______________________________________________
Inclined Planes
 _______________________________________________
_______________________________________________
Wedge
 _______________________________________________
_______________________________________________
Screw
 An ____________________________________________
 Screws with threads that are closer together moves
forward less for each turn of the screw.
Pulleys
 _______________________________________________
______________________________________________
 Fixed pulleys – __________________________________
 _________________pulleys – attached to the object
being moved rather than to a fixed location.
 Pulley System – __________________________________
________________________________________________
Compound Machines
 _______________________________________________
_______________________________________________
 Car, washing machine, clock