Simplifying Assumptions

The world is complex. Every situation has many possible factors to take into account. Often however many of these possible factors are irrelevant and can be ignored. For example, we would not expect the temperature to greatly influence the acceleration due to gravity so can ignore this factor. Even if a factor cannot be ignored, we can often gain insight into a phenomenon by ignoring it. A model can later be refined by taking more factors into account not making that simplifying assumption.

The table below lists some common assumptions.

 Assumption Examples Friction is negligible PulleyThe motion of a car down or up a slope No heat lost Heat being transferred from one body to another when both are insulated together Mass of string or spring is negligible Simple pendulumMass on stretched spring Resistor of ammeter is zero Electric circuits Resistance of voltmeter is infinite Electric circuits Internal resistance of battery is zero Electric circuits Conductor obeys Ohm's Law Electric circuits 100% efficiency TransformersProjectiles Gas is ideal Thermodynamics Collision is elastic Collisions. In fact perfectly elastic collsions are only possible between atoms and subatomic particles. 