Science Machines Quiz
mechanical efficiency
The efficiency of a machine is the ratio of the output work to the input work.
fixed pulley
A fixed pulley is attached to something that does not move. A fixed pulley only changes the direction of the force. The mechanical advantage is 1. changes direction of force cord to open window blind is ex.
lever
A lever is a simple machine made up of a bar that pivots, or rotates, about a fixed point. The point about which a lever pivots is called a fulcrum. Levers are used to apply an output force to a load.
moveable pulley
A moveable pulley is attached to the object being lifted. They do not change the direction of the force. Moveable pulleys decrease the force needed to lift an object. The distance over which the force acts increases. The mechanical advantage is 2. elevator, construction cranes
pulley
A pulley is a simple machine that is a grooved wheel with a rope or a cable wrapped around it.
block and tackle
A pulley system is a combination of fixed and moveable pulleys that work together. The mechanical advantage is equal to the number of ropes pulling up on the object. decreases force and changes distance of force
MA equation
Output force/input force Fout and Fin are in Newtons, MA has no units
input arm and output arm
The distance from the fulcrum to the input force is the input arm The distance from the fulcrum to the output force is the output arm.
third class lever
The input force is between the output force (load) and the fulcrum. The output force is less than the input force. You apply a greater force over a smaller distance. The output force and the input force act in the same direction. The mechanical advantage is always less than 1. examples: tweezers, rake, broom, fishing rod
second class lever
The output force (load) is between the input force and the The output force and the input force act in the same direction. The output force is greater than the input force. They allow you to apply less force over a greater distance. The mechanical advantage is always greater than 1. example: wheelbarrow, nutcracker
why does output work never exceed input work
The reason for this is friction. Friction converts some of the input work to thermal energy.
compound machine
Two or more simple machines that operate together form a compound machine. Examples are a can opener and gears. Each simple machine decreases the overall efficiency of a compound machine.
input work and output work
Work input is the work you do on the machine. It is the input force x the distance the force was applied. The work output is the work the machine does. It is output force x the distance the machines moves in the direction of the output force.
input force and output force
You apply an input force that moves part of the machine and does work. Machines convert, or change, input work to output work. They do this by applying an output force on something and making it move. Input force is the force you apply on the machine. The output force is the force the machine applies on the load.
where should you sit on a see saw to make it easiest to lift person on other side, why
as far as possible from fulcrum bigger input arm greater distance so greater input force
first class lever
fulcrum between input force and output force direction of input force is different from output force MA is less than, greater than, or equal to 1 the closer the fulcrum to the output force, the greater the MA examples: scissors, see saw decreases input force needed
machines
is any device that makes doing something easier.All machines make tasks easier, but they do not decrease the amount of work required. Instead, a machine changes the way in which the work is done.
mechanical advantage
is the ratio of a machine's output force produced to the input force applied. The mechanical advantage, or MA, tells you how many times larger or smaller the output force is than the input force. can be <1, >1 or =1
efficiency equation
output work/input work times 100
what can increase efficiency?
reducing friction by lubricating a machine's moving parts increases efficiency.
How do use a machine?
you must apply input force to it, The machine changes the input force into an output force.
inclined plane
A ramp, or inclined plane, is a flat, sloped surface. It takes less force to move an object upward along an inclined plane than it does to lift the object straight up. Increasing the length and decreasing the height of the inclined plane increases its mechanical advantage. The longer or less-sloped an inclined plane is, the less force is needed to move an object along its surface. decreases force to move object formula=length of slope/height of slope >1
screw
A screw is an inclined plane wrapped around a cylinder. The longer the screw and the closer together the threads are, the greater the mechanical advantage >1 Example: a jar lid
wedge
A sloped surface that moves is called a wedge. It is often used for cutting. A wedge is really a type of inclined plane with one or two sloping sides. The longer and thinner the wedge is, the greater its mechanical advantage. always >1 example: teeth, knife blade, doorstop
wheel and axle
A wheel and axle is an axle attached to the center of wheel and both rotate together. Axle is another word for shaft When an input force is applied to turn the wheel, the smaller axle rotates a shorter distance makes the output force greater than the input force The mechanical advantage is greater than 1 examples: doorknobs, wrenches, screwdrivers, steering wheel always >1
Why is efficiency always less than 100%
Because output work is always less than input work, a machine's efficiency is always less than 100%.
3 ways machine makes work easier
Change the Size of a Force (Although the output force is greater than the input force it acts over a shorter distance. ) Change the Distance a Force Acts (The force applied by the rake (the output force) decreases as the distance over which the force acts (the output distance) increases. ) Change the Direction of a Force
