Two identical moving boxes sit by the door: one packed with books, one packed with pillows. Same size, same shape. They are not the same, and the difference is not their size.
The difference is how much stuff each box holds.
The books box holds far more stuff, more matter, than the pillows box. Mass measures that: the quantity of matter in an object.
Mass is measured in kilograms, written kg, the SI base unit for mass.
What does an object's mass measure?
An anchor to hold on to: a liter bottle of water has a mass of about 1 kg. Two more anchors: a baseball has a mass of about 0.15 kg, and a bowling ball about 6 kg.
Which has a mass of about 1 kg?
Mass follows the matter. Squash a ball of clay flat, and its mass does not change: same stuff, same mass.
Jax flattens a 0.5 kg ball of clay into a pancake. Is the pancake's mass still 0.5 kg?
Mass says nothing about size. The pillows box is just as big as the books box; it simply holds less matter.
Two same-size coolers sit on a porch: one empty, one full of ice. Which has more mass, and why?
Mass measures the quantity of matter.
The full cooler holds everything the empty one does, plus the ice.
The full cooler: it holds more matter, so it has more mass.
About what is the mass of a full 2-liter bottle of soda?
A liter bottle of water has a mass of about 1 kg, and soda is mostly water.
This bottle holds twice the liquid.
About 2 kg.
Two identical duffel bags are packed for a trip: one holds a laptop and books, the other a single jacket. Which statement is correct?
Which reading could be a mass?
A camper rolls her sleeping bag from a loose bundle into a tight cylinder a quarter of the size. The sleeping bag's mass: