Chapter 6 - Work & Machines

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```					Physical Science Ch. 6 Study Guide Answers
II. Give the definition…
Work                       Transfer of energy that occurs when a force makes an object MOVE
Power                      Work done over time
Mechanical advantage The number of times a machine multiples the input force
Efficiency                 Work output of a machine divided by the work input
THERMAL Energy             Energy created by friction when a machine does work
Simple machine             A machine that does work with only one movement
Lever                      Bar that is free to pivot about a fixed point
Fulcrum                    Fixed point on a lever
Ideal mechanical           Mechanical advantage without friction
advantage                  For a lever = Length of input arm divided by length of output arm
Pulley                     A grooved wheel with rope, simple chain, or cable running along a groove
Wheel & axle               Machine with two wheels of different sizes rotating together
Inclined plane             Sloping surface that reduces the amount of force required to do work
Screw                      Inclined plane wrapped in a spiral around a cylindrical post
Wedge                      Inclined plane with one or two sloping sides
Compound Machine           Device that is made up of more than one simple machines
Effort force               The force you apply to a simple machine, input force
Resistance force           Output force, the force applied by the machine

1.   The unit of power is the Watts
2.   How does friction influence mechanical advantage of a machine?
Because of friction, mechanical advantage is never 1, some energy is lost to heat
3.   What happens to energy when work is done?
When work is done, transfer of energy always occurs
4.   Do all machines multiple the force applied to them?
Machines make work easier by increasing the force applied to an object
5.   Is it every possible to get more work out of a machine than you put into it? No
6.   An inventor claims to have built a machine that can produce 120 J of work with an
input of 110 J. Would you believe the inventor's claim? Why or why not?
The inventor’s claim would be false because the efficiency of the machine would
be 108% and no machine can have an efficiency greater than 100% because
output can not be more than input.
7.   Explain why adding oil to the moving parts of a machine can increase its efficiency.
Adding oil decreases friction, which decreases work lost to heat increasing work
output and efficiency.
Ideal Mechanical advantage does not take energy lost to friction into account,
9.    When a machine is used to perform a task, what is the relationship between work
output and work input?
Work output is always less than work input due to energy lost to friction
10.   What three simple machines make up the lever family?
Lever, Pulley, Wheel & Axle
11.   True or False – all three classes of levers can be found in the human body.
True, see pg. 168
12.   Describe the three types of pulleys.
Fixed = attached to something that does not move
Movable pulley = one end of the rope is fixed and the wheel is free to move
Block & Tackle = system of pulleys consisting of fixed and movable
13.   A fixed pulley makes work easier by doing what?
Changes direction of force
14.   Find the ideal mechanical advantage of the inclined plane shown in Figure 5-2.
IMA = l/h (length divided by height) 12/4 = 3
15.   What is the ideal mechanical advantage of THE second-class lever?
IMA = Le/Lr = 4/1 = 4
16.   Open Response:
A. Draw and label a simple machine.
Can draw lever, pulley, wheel & axle, inclined plane, wedge, or screw
B. Describe three uses of the simple machine.
Various uses depending on machine, see notes and book

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Jun Wang Dr
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