# Wikijunior:How Things Work/Glossary

### Force

• Force — An expression of the ability to push, pull, twist or accelerate a body.
• Mechanical Advantage — The ratio of the force produced by a machine to the applied input force.
• Work — A measure of energy expended in moving an object. Force times distance equals work (F*D = W).

### Motion

• Motion — The body said is in motion if its position changes with respect to time.
• Rest — A body said to be in rest if its position does not changes with respect to time.
• Distance — It is the length of the actual path traversed by the body between its initial and the final positions.
• Displacement — It is defined as the change in the position of the object in a fixed direction.

### Electricity

• Electricity — Electricity is the flow of electrons in a conductor.
• Ohm — The SI unit measuring the electrical resistance.
• Mega-ohm — A unit of electrical resistance which is equal to one million ohms.
• Ampere — The basic SI unit measuring the quantity of electricity.
• Ohmmeter — Ohmmeter is an instrument for measuring resistance in a conductor. The unit used is in ohms.
• Mega-ohmmeter — An instrument for measuring extremely high resistance. The unit used is mega-ohm.
• Ammeter — An electric meter used to measure current. The unit used is in amperes.
• Voltmeter— A voltmeter is an instrument used for measuring the potential difference (voltage) between two points in an or electronic circuit.
• Voltage Drop — The loss of voltage between the input to a device and the output from a device due to the resistance of the device.
• Potential Difference — The difference in electrical potential (voltage) from one point in an electric circuit to another point.
• Direct Current (DC) — The current flowing in one direction only.
• Alternating Current (AC) — The current flow which first goes one way and then reverses it's direction at regular time interval.
• Battery — These are devices which convert chemical energy into electric energy.