# Mechanical Advantage and Simple Machines - Key terms

### COMPOUND LEVER:

A machine that combines multiple levers to accomplish itstask. An example is a piano or manual typewriter.

### CLASS I LEVER:

A lever in which the fulcrum is between the input force and output force. Examples include a crowbar, a nail puller, and scissors.

### CLASS II LEVER:

A lever in which the output force is between the input force and the fulcrum. Class II levers, of which wheelbarrows and bottle openers areexamples, maximize output force at the expense of range of motion.

### CLASS III LEVER:

A lever in which the input force is between the output force and the fulcrum. Class III levers, of which a fishing rod is an example, maximize range of motion at the expense of outputforce.

### EFFICIENCY:

The ratio of actual mechanical advantage to theoretical mechanical advantage.

### FRICTION:

The force that resists motion when the surface of one object comes into contact with the surface of another.

### FULCRUM:

The support point of alever.

### INERTIA:

The tendency of an object in motion to remain in motion, and of an object at rest to remain at rest.

### INPUT:

The effort supplied by the operator of a machine. In a Class I lever such as a crowbar, input would be the energy one expends by pushing down on the bar. Input force is often called applied force, effort force, or simply effort.

### LEVER:

One of the three basic varieties of machine, a lever consists of a rigid bar supported at one point, known as the fulcrum.

### LEVER ARM:

On a lever, the distance from the input force or the output force to the fulcrum.

### MACHINE:

A device that transmits or modifies force or torque for a specific purpose.

The ratio of force output to force input for amachine.

### MOMENT ARM:

For an object experiencing torque, moment arm is the distance from the pivot or balance point to the vector on which force is being applied. Moment arm is always perpendicular to the direction of force.

### OUTPUT:

The results achieved from the operation of a machine. In a Class I lever such as a crowbar, output is the moving of a stone or other heavy load dislodged by the crowbar. Output force is often called the load or resistance force.

### TORQUE:

In general terms, torque is turning force; in scientific terms, it is the product of moment arm multiplied by force.