Mass = measure of the amount of matter within an object Density = mass per unit of volume Example: Think of one pound of gold and one pound of aluminum, at sea level on earth. They contain the same mass, but the mass is more dense in the gold, because its volume is much smaller.
To assert is defined as  to make a statement with full confidence of its truth and factuality. An example of a person who may assert something is a scientist who is very confident in his supporting data. The definition of assert is to make a claim or defense. An example of someone who may assert is a defense attorney who believes strongly in his client's innocence. To assert yourself means to make your beliefs or desires known in a strong and forceful way.
assume verb [T] (TAKE CONTROL). C2 to take or âbegin to have âresponsibility or âcontrol, sometimes without the âright to do so, or to âbegin to have a âcharacteristic: The new âpresident assumes âoffice at âmidnight âtonight. The âterrorists assumed âcontrol of the âplane and âforced it to âland in the âdesert.