Science Focus Topic 3 Notes: Mass and Forces | Print |
 Mass The mass of an object is the measure of the amount of matter in it. The mass is the number of particles the substance has A small cylinder of metal was used, as a standard, by which, to compare different substances. This standard (in the metric system) is called the primary standard of mass, and the amount of material in it is called one kilogram (kg). Smaller masses are measured in grams (g). 'Kilo' means one thousand (1000) and is equal to 1000 grams. Very small masses are measured in milligrams (mg). 1000 mg. equal 1 g. A balance is used to measure the amount of mass in a particular substance. Standard scientific balances include the triple beam balance and the equal arm balance. Mass stays the same no matter where you are in the universe. Forces and Weight Force is a push or pull on an object. The standard unit of force is called a newton (N). (1 newton of force will stretch a thin rubber band, or will be what it takes to lift up a D-cell battery). A force meter (spring scale) is used to measue the amount of force - the pull of gravity - on a mass. To describe a force accurately, you need to determine its direction and size. Weight Weight is a force and should properly be measured in newtons. Sir Isaac Newton (Did You Know - p. 300) described the force that pulls objects together as the force of gravity. The gravitational forces between two objects depends on the masses of the objects and the distance between them. This gravitational force is called weight. Because gravitational force depends on the distance between two objects, an object's weight changes depending on where it is. (the farther away from the earth, the less the weight. REMEMBER: Mass is the amount of matter an object is made of and weight is the force with which gravity pulls on an object. Picturing Forces A force diagram is a simple picture that uses arros to show the strength and direction of one or more forces (a longer arrow represents a larger force and a wider arrow represents a stronger force) Topic 3 Review p. 304