On National Teacher Day, meet the 2024-25 Kenan Fellows
Work and Machines
1. Which activity require the least amount of work?
Carrying
heavy books home
Reading a 300-page novel
Skiing for 1 hour
Lifting a 45 kg mass
Holding a steel beam in place for 3 hours
Jacking up a car
3. By the end of this section, you should be able to:
Determine
when work is being done on an
object.
Calculate the amount of work done on an object.
Explain the difference between work and power.
4. Work
is the transfer of energy to an object by
using a force that causes the object to move in
the direction of the force.
One
way you can tell that work is being done is
that energy is transferred.
5. a force doesn’t always result in work
being done.
Applying
For
work to be done on an object, the object
must move in the same direction as the force is
applied.
13. It
may take you longer to sand a wooden shelf
by hand than by using an electric sander, but the
amount of energy needed is the same either
way. Only the power output is lower when you
sand the shelf by hand.
17. By the end of this section, you should be able to:
Explain
how a machine makes work easier.
Describe and give examples of the forcedistance trade-off that occurs when a machine is
used.
Calculate mechanical advantage.
Explain why machines are not 100% efficient.
18. A
machine is a device that makes work easier by
changing the size or direction of a force.
20. The
work that you do on a machine is called
work input.
The
work done by the machine on an object is
called work output.
Machines
allow force to be applied over a
greater distance, which means that less force
will be needed for the same amount of work.
21. Machines
make work easier by changing the
size or direction of the input force.
When
a machine changes the size of the force,
the distance through which the force is exerted
must also change.
25. The
less work a machine has to do to overcome
friction, the more efficient the machine is.
Mechanical
efficiency is a comparison of a
machine’s work output with the work input.
29. What type of machine can be found on at least half
of the people in this room right now?
30. By the end of this section, you should be able to:
Identify
and give examples of the six types of
simple machines.
Analyze the mechanical advantage provided by
each simple machine.
Identify the simple machines that make up a
compound machine.
31. A lever
is a simple machine that has a bar that
pivots at a fixed point, called a fulcrum.
With
a first-class lever, the fulcrum is between
the input force and the load.
32. The
load of a second-class lever is between the
fulcrum and the input force.
33. The
input force in a third-class lever is between
the fulcrum and the load.
35. A
pulley is a simple machine that consists of a
wheel over which a rope, chain, or wire passes.
A fixed
pulley is attached to something that does
not move.
36. Unlike
fixed pulleys, movable pulleys are
attached to the object being moved.
When
a fixed pulley and a movable pulley are
used together, the pulley system is called a
block and tackle.
37.
38. A wheel
and axle is a simple machine consisting
of two circular objects of different sizes.
39. The
mechanical advantage of a wheel and axle
can be found by dividing the radius (the distance
from the center to the edge) of the wheel by the
radius of the axle.
40. An
inclined plane is a simple machine that is a
straight, slanted surface.
The
mechanical advantage (MA) of an inclined
plane can be calculated by dividing the length of
the inclined plane by the height to which the load
is lifted.
41. A wedge
is a pair of inclined planes that move.
Mechanical
advantage of wedges can be found
by dividing the length of the wedge by its
greatest thickness.
42. A screw
is an inclined plane that is
wrapped in a spiral around a
cylinder.
The
longer the spiral on a screw is
and the closer together the threads
are, the greater the screw’s
mechanical advantage is.
43. Compound
machines are machines that are
made of two or more simple machines.
The
mechanical efficiency of most compound
machines is low, because compound machines
have more moving parts than simple machines
do. Thus, there is more friction to overcome.
