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5-3: Simple & Compound Machines + Mechanical Advantage
Terms in this set (41)
What is an inclined plane?
A sloped surface connecting a lower surface to a higher surface (it is a ramp)
In an inclined plane the distance input > the distance output (IMA > 1), this means that
And inclined plane multiplies your force
What is a wedge?
A wedge is two inclined planes put together (chisel, knife, ax)
In a wedge, since the distance input > the distance output (IMA > 1), this means that
A wedge multiplies your force
What is a screw?
An inclined plane wrapped around a cylinder
In a screw, since the distance input > the distance output (IMA > 1), this means that
A screw multiplies your force
What is a lever?
A bar that rotates around a fixed point called a fulcrum
There are ___ classes of levers each of which are used for different things.
What are a wheel and axle?
Two connected rings or cylinders, one inside the other, which both rotate in the same direction around a single center point.
The smaller cylinder is the axle and
The larger cylinder is the wheel
On a wheel and axle, the input force may be applied to
either the wheel (MA > 1) or the axle (MA < 1) depending on the use of the machine
What is a pulley?
A simple machine that consists of a rope that fits into a groove in a wheel / when the rope is pulled the wheel moves
A pulley can have a
MA = 1 or MA > 1
What is a compound machine?
A machine made up of two or more simple machines
What are some examples of compound machines?
Wheelbarrow (second-class lever & a wheel and axle)
Scissors (lever & wedge)
What is the mechanical advantage (MA) of a compound machine?
The product of the MA of each simple machine / this means that compound machines have greater MA
What is the mechanical advantage equation for a compound machine?
MA compound = MA simple x MA simple
Efficiency of compound machines re generally
Lower (as a result of increased friction)
What is mechanical advantage?
How much a machine changes the input force
Output force/input force= Mechanical advantage
Note that this equation represents the actual mechanical advantage of a machine. The actual mechanical advantage takes into account the amount of the input force that is used to overcome friction. The equation yields the factor by which the machine changes the input force when the machine is actually used in the real world.
The ideal mechanical advantage represents what?
the change in input force that would be achieved by the machine if there were no friction to overcome.
The ideal mechanical advantage is always ________ than the actual mechanical advantage because all machines have to overcome friction. Ideal mechanical advantage can be calculated with the equation:
Ideal mechanical advantage =
input distance/output distance (notice how it is labeled DISTANCE)
A hammer has an input distance of 3 cm and an output distance of 9 cm. What is its ideal mechanical advantage?
AMA= Output force/input force -
Notice how it is labeled FORCE
To open a soda can lid, a force of 50 N is applied to a car key, which acts as a lever. If the car key applies a force of 400 N to the lid, then the mechanical advantage of the car key is ________.
(Output force/input force) 8N
The sloping surface of the inclined plane supports part of the weight of the object as it moves up the slope. As a result, it takes less force to move the object uphill.
The trade-off is that the object must be moved over a greater distance than if it were moved straight up to the higher elevation.
The more gradual the slope of the inclined plane,
the less input force is needed and the greater the mechanical advantage.
Examples of inclined planes include
The mechanical advantage of an inclined plane is always
Greater than 1
A wedge applies more force to the object (output force) than the user applies to the wedge (input force),
so the mechanical advantage of a wedge is greater than 1. A longer, thinner wedge has a greater mechanical advantage than a shorter, wider wedge. With all wedges, the trade-off is that the output force is applied over a shorter distance, so force may need to be applied to the wedge repeatedly to push it through the object.
Why is it harder to turn a screw with more widely spaced threads?
The screw moves farther with each turn when the threads are more widely space, so more force must be applied to turn the screw and cover the greater distance.
Other levers change force or distance in different ways than a hammer removing a nail. How a lever changes force or distance depends on the location of the input and output forces relative to the fulcrum. The input force is the force applied by the user to the lever.
The output force is the force applied by the lever to the object.
When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force.
This occurs only with first-class levers.
When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change.
This occurs with both second-class and third-class levers.
When the input force is applied farther from the fulcrum than the output force is, the output force is greater than the input force, and the ideal mechanical advantage is greater than 1.
This always occurs with second-class levers and may occur with first-class levers.
When the input force is applied closer to the fulcrum than the output force is, the output force is less than the input force, and the ideal mechanical advantage is less than 1.
This always occurs with third-class levers and may occur with first-class levers.
When the input and output forces are the same distance from the fulcrum, the output force equals the input force, and the ideal mechanical advantage is 1.
This occurs only with first some first-class levers.
When the input force is applied to the axle, as it is with a Ferris wheel, the wheel turns with less force. Because the output force is less than the input force, the mechanical advantage is less than 1.
However, the wheel turns over a greater distance, so it turns faster than the axle.
When the input force is applied to the wheel, as it is with a doorknob, the axle turns over a shorter distance but with greater force, so the mechanical advantage is greater than 1.
This allows you to turn the doorknob with relatively little effort, while the axle of the doorknob applies enough force to slide the bar into or out of the doorframe.
Because compound machines have more moving parts than simple machines, they generally have more friction to overcome.
As a result, compound machines tend to have lower efficiency than simple machines.
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