Drawing

DEPCOllc

3305 Airport Drive | Pittsburg, KS 66762

Lesson 2: Mass, Gravity, Weight and Density

Visualizing and Describing The Science of Totally Trebuchet

Mass is the measure of the amount of material in an object. It is the nature of all mass to be

mutually attractive. This force of attraction is called gravity.

Gravity is proportional to mass. Therefore the most significant gravitational force is due to the

earth itself.

Weight is the measure of the downward force created by the mutual gravitational attraction

between the mass of an object and the mass of the earth.

Objects of the same size and shape (volume) can have different amounts of mass. The 1-1/2Ǝ

(38mm) diameter lead sphere used as the GEARS trebuchet counterweight has significantly more

mass than the (38mm) diameter wood sphere found in the kit. These spheres have equivalent

volumes, but not equivalent masses. Since weight is the result of gravity acting on mass, the

1-1/2Ǝ (38mm) diameter lead sphere weighs more than the 1-1/2Ǝ (38mm) diameter wood sphere.

The lead sphere contains more mass per unit volume. Density is a measure of the mass per unit

volume of an object. Weight can be substituted for mass when the density of an object or a

substance is calculated. Units of mass and volume are kilograms per cubic meter (kg/m

in SI

units) or in pounds per cubic foot (lbs/ft

in imperial units.)

In this lesson we will explore some fundamental properties of matter and materials in an effort to

better understand and explain the operations of trebuchets and other mechanical systems.

Mass

Mass is a fundamental quantity measured in kilograms or slugs.

SI units are kilograms (kg) Imperial units are slugs.

Mass is a scalar quantity, it can only be expressed as a magnitude.

All objects have mass. Mass is a measure of the amount of matter or

material an object contains.

Mass

The sum of all

material in an

object

Another example of a fundamental quantity is length. All objects

have length.

An 8-inch long (203mm) pencil measures 8 inches long (203mm), anywhere in the universe.

Length, mass and time are fundamental quantities that can be measured and compared

irrespective of other factors or frames of reference (Quantum mechanics and relativity excluded).

Sample Science Curriculum