Units of Measurement Flashcards
What is a unit?
A standard for comparison used in the measurement of a quantity.
What is magnitude?
Magnitude is a multiple of a unit.
How are the three basic quantities of mechanics related?
By Newton’s Second Law: F=ma.
1. F represents force.
2. m represents mass.
3. a represents acceleration (which is derived from the rate of change of displacement, ergo length and time).
When is Newton’s Second Law valid?
When three of the basic quantities of mechanics are given, and a fourth HS to be derived from the equation: F=ma.
Why can’t units of the basic quantities of mechanics be devised arbitrarily?
Because quantities are related by Newton’s Second Law, each one must be derivable by the equation. This can only hold true if the units are related, too.
*** The unit of force Newton (N=Kg.m.s-¹) is derived from the equation.
What is a Newton?
A Newton is a the amount of force needed to accelerate a 1kg body by 1m.s-².
What is the International System of Units (SI)?
A. It is a modern version of the metric system
** (MKS). SI stems from the French: “Systeme International d’Unites”.
** The unit of time is the second (s)
** The unit of mass is the kilo-gram (kg)
** The unit of length is the meter (m)
*** The unit of force is derived from the other three Newton (N=kg.m.s-²)
What is the US. Customary System?
A system of measurement used primarily in the United States.
** The unit of length is the Foot (ft)**
The unit of time is the second (s)
The unit of force is the Pound (lb)
The unit of mass is the Slug (lb.ft.s-²)
*To validate Newton’s Second Law, in the US. Customary System, the unit of mass (slug=lb.ft.s-²) is derived from length (ft), time (s), and force (lb).
