an object at rest remains at rest, and an object in motion continues with constant velocity, unless acted on by a net force.

 

acceleration of an object is proportional to the net force acting on it and inversely proportional to its mass.

 

whenever one object exerts a force on another object, the second object exerts an equal and opposite force on the first object.

 

one member of an action–reaction pair of forces that is equal in strength and opposite in direction to the action force that is its counterpart.

 

η= E out/E in

Einitial=Efinal
Wnet=ΔEk 
ΔE=0

System

group of related and interacting objects and influences that we choose to investigate. A system can be open or closed.

resistive force caused by motion that always acts to oppose motion.

isolated system that cannot exchange matter or energy with its surroundings.

particular configuration of all the elements in a system, usually in reference to a defined energy of the system.

 
Efficiency

ratio of the output energy or power divided by the input energy or power for any process that transforms energy. (Note that input and output can be defined in different ways.) 

total energy in a closed system does not change over time. While energy cannot be created or destroyed, it can be transformed from one form to another, just as long as the total energy remains constant.

Open system

system on which outside influences can act, such that matter or energy can be added or removed from the system.

Work–energy theorem

change in the kinetic energy of an object equals the network done on it.

 

action on a body that causes change in motion. Measured in newtons (N).

 

form of energy equal to one newton of force exerted for one meter in the direction of the force. Measured in joules (J).

ratio of the output force to the input force for a machine.

 

mechanical device that uses only one kind of motion to change the magnitude or direction of a force. The six kinds of simple machines are lever, pulley, wheel and axle, ramp, wedge, and screw.

 

ratio of the output energy or power divided by the input energy or power for any process that transforms energy. (Note that input and output can be defined in different ways.)

 
Ideal mechanical advantage

ratio of the distance moved by the input force to the distance moved by the output force. The ideal mechanical advantage corresponds to a machine with no efficiency losses.

Gear ratio

ratio between the rates that the last gear and the first gear rotate in a machine.

Input force

force applied to a machine.

force produced by a machine.

rate at which a cyclic behavior repeats. Measured in hertz (Hz), where 1 Hz = 1 cycle per second or 1/s. Frequency is the inverse of the period.

 
Oscillator

system that exhibits harmonic motion.

 

condition where the frequency of a periodic force matches a natural frequency of an oscillating system. At resonance, energy accumulates over many cycles of the periodic force and oscillations can become very large, even when the causative force is relatively small.

 

time it takes to complete one full cycle of an oscillation. Equal to the inverse of the frequency of oscillation.

 

maximum displacement of an oscillation from its equilibrium, or average, value.

Damping

gradual decrease in amplitude and energy of a wave due to friction or other energy-loss mechanisms.

something that repeats in time at regular intervals, such as one full swing of a pendulum.