The terms mass and weight have very different meanings in chemistry. The literal meanings depend on different properties of objects.

Mass is a measure of the amount of matter or stuff in an object. For a specific thing like a nut or bolt the mass will be the same regardless of where it is.

Weight is a property that depends on the gravitational force acting on an object. This force results from the attraction one mass has for another. The magnitude of the attraction depends on the distance between the masses and their sizes. This force will vary with location.  Astronauts experience weightlessness when they go into space because they are far away from any large mass and its gravitational pull or force.

The European Space Agency, ESA, launched the GOCE satellite to map the Earth's gravity accurately. click here for more and here for GOCE video .  We usually are on or near the surface of the Earth and we experience a pretty constant pull from the gravitational field of the Earth. .  The differences in the Earth's graviational force are illustrated in the false color image shown here.  The red areas have a stronger gravitational pull and the blue ones have a weaker gravitational pull. Gravity does not exert an equal pull or force everywhere on the Earth's surface. Gravity differs because of the Earth's rotation, differences in the density of the interior of the Earth and the topography of the surface such as mountains or bodies of water.

A person's weight would be very different on Mars or Jupiter because their masses are not the same as the Earth's. A person who weighs 100 pounds on the Earth would weigh roughly 38 pounds on Mars and 236 pounds on Jupiter. The illustraton below shows how much a 100 pound earthling would weigh on various planets .

Weight behaves like real estate. Weight depends on location, location, location! click to see your weight on Mars, Mercury, etc

How to measure weight and mass

How is mass measured? Why should anyone worry about it? I was afraid you would never ask. Lets deal with reasons why we are interested in measuring mass. Most everyone has had a prescription. The instructions for taking a drug are related to a person's body mass like milligrams per kilogram of body mass. It is essential to know how much mass a person has so the doseage is adequate. It cannot be not too small or it will be ineffective and it cannot be too strong to produce harmful side effects. The money we pay for groceries like meat, fish, fruits and vegetables depends on accurate measurements of the amount of stuff in the item. What do you want measured mass or weight?  We want the right dose of a medication. We want our moneys worth at the market.

We measure mass with a balance and we use a scale to measure weight. When we use a balance the mass of calibrated masses are used to offset or counter balance the mass of the object we are measuring (often we refer to this as weighing and object). A spring scale is often used to measure weight. The spring is calibrated to stretch a measured amount for known weights.