The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho).

There are two kinds of density, "weight density" and "mass density". We will only use mass density and when we say: "density", we will mean "mass density".

Density is mass per volume. Lead is dense, Styrofoam is not. The metric system was designed so that water will have a density of one gram per cubic centimeter or 1000 kilograms per cubic meter.
Lead is about 10 times as dense as water and Styrofoam is about one tenth as dense as water.

here is a link for further explaination of density

http://www.youtube.com/watch?v=rxb_6UANXqU

here is a link of a animation on how density of an object causes it to float or sink in water.

http://www.youtube.com/watch?v=KALbn7kRx_Y

How to distinguish between mass and weight?

this is a video distinguishing difference between Mass and Weight
http://www.youtube.com/watch?v=grWG_U4sgS8

weight=massxgravitational field strength

(w=mg)

The weight of an object can be measured using:

Gravitational Field Strength,g
Defined as the gravitational force acting per unit mass on an object.

On Earth the gravitational feild strength is about 10N/kg

1kg of mass experiences a force of 10N due to Earth's gravitational pull.

gravitational field strength is equivalent to acceleration of free fall

Question:why would your weight decrease if you are on the moon
Answer:because moon has a lower gravitational field strength.Infact,you would be 1/6 of your's Earth weight on the moon

Gravity is an attractive force. This doesn't mean it's pretty. What "attractive" means is that an object's gravity pulls other objects toward it.
The Earth's gravity naturally pulls us, and everything else, toward the center of the planet, which keeps us from drifting off into space.

The force of gravity is the force with which the Earth,Moon,or other massive body attracts an object towards itself.
The Earth isn't the only thing that has gravity. In fact, every single object in the universe has gravity.

Gravitational field is a region in which a mass experiences a force due to gravitational attraction.

here is a video showing what is gravity

http://www.youtube.com/watch?v=Uy3nATe85Kg

The inertial mass of an object determines its acceleration in the presence of an applied force. According to Isaac Newton's second law of motion, if a body of mass m is subjected to a force F, its acceleration a is given by F/m
Inertial mass (which leads to momentum) is a measurement of a body's resistance to a change in velocity when an external force is applied to that body.


here is a video that further explain the term inertial
http://www.youtube.com/watch?v=by-7kkAu2Pg

In physics, mass (from Ancient Greek: µ??a) commonly refers to any of three properties of matter, which have been shown experimentally to be equivalent: inertial mass, active gravitational mass and passive gravitational mass.

In everyday usage, mass is often taken to mean weight, but in scientific use, they refer to different properties.

Mass is the amount of matter or substances in a body.

Mass is a scalar quantity

SL unit for mass is kilogram

The mass of an object can be measured using:

here is a video further explaining what is mass

http://www.youtube.com/watch?v=uvy4nWh0KwE

credits

google.com.sg

wikipedia.org

google.com.sg/image

youtube.com

http://faculty.ccc.edu/colleges/wright/science/physics221/P221Ws4.htmm

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