Mass as a Physical Property

By Moira Whitehouse PhD

We have been studying the properties of matter.

Some properties of matter are its color, its texture or whether or not it is shiny or dull.

Another property of matter is its mass.

The more stuff in an object the more mass it has and

The mass of an object is the amount of matter or “stuff” in the object and it is very closely tied to its weight.

the more it weighs.

The mass of objects is one of the properties that scientists measure.

But before we discuss how to measure mass let us look at what mass means and how it is related to weight.

This Great Dane weighs more than the Chihuahua. It has more mass – more matter in its body.

Who has more mass, Winnie the Pooh & friends or the elephant?

The side of the teeter totter with the elephant, who has more mass, goes down and the side with Winnie and friends, with less mass, goes up.

The elephant has more mass than Winnie the Pooh & friends.

Look at this young man and woman sitting on a teeter totter..

On a teeter totter they balance.

It means that the young man and young woman weigh the same amount and

What does this mean?

have the same amount of mass.

Who has more mass—Linus or Charlie Brown?

What has more mass—the donut or the apple.?

So let’s review what we have learned about the mass of an object.

First, what is mass?

Mass is how much matter or “stuff” is inside something.

The more stuff inside of an object the more mass it has and the more it weighs.

How are mass and weight related to each other?

The mass of an object stays the same, but the objects weight can change. The reason something’s weight can change is that weight depends on gravity.

So how are mass and weight different from one another?

Things, including people , weigh less on the Moon than they do on Earth because the Moon has less gravity than Earth.

This boy weighs 60 pounds on Earth.

On the Moon, he would weigh only 10 pounds.

Because the Moon has 1/6 as much gravity as Earth, his weight has changed.But his mass—the amount of stuff inside of him—stays the same.

Now let’s look at how the mass of something is measured.To measure something, we need two things:

a tool

units

and

with which to measure

with which to compare

•a balance scale

The mass of an object is measured with a tool called:

And an object’s mass is measured in units called:

grams (g)

kilograms (kg)

(for smaller objects)

(for larger objects)

and

In the lab we use pieces of brass or plastic marked with their mass as standard units of mass.

Like these:

Or these:

20 g

10 g

5 g

1 g

•But where do we come up with these “known masses”?

Now we know that the tool to measure mass is the balance scale and the units are grams and kilograms, how does a balance scale work?

It is like the teeter totter we saw earlier.

When two objects with the same mass are placed on a balance scale, gravity pulls equally on both objects and the trays stay balanced.

•But if one object has more mass than the other:

You know what’s going to happen.

•Sure the more massive object being pulled by more gravity goes down.

And the less massive object goes up.

These two fossils in the left pan and the steel balls in the right pan balance on the scale. What can you say about the mass of the two fossils and the steel balls?

• If we balance the object in the red tray with the known masses in the yellow tray

We will learn the mass of the object in the red tray.

•We have the tool (a balance scale) and the standard unit ( the gram); the only other thing we need to find the mass of an object is a procedure.

•The procedure to follow is in the next slides.

1. Place the object in one tray.

2. Place the largest mass in the other tray.

•The 500g mass is greater than the mass of the pumpkin, so REMOVE it and replace it with the second largest mass.

3. Place the second largest mass in the other tray.

•The 200g mass is also greater than the mass of the pumpkin, so remove it and place the third largest standard mass on the tray..

3. Place the third largest mass in the tray.

•Ah, the 100g mass is less than the mass of the pumpkin, so LEAVE it in the tray and ADD THE NEXT largest standard mass on the tray.

Ok, the 100g and the 50g masses are equal to the mass of the pumpkin.

And we say the pumpkin has a mass of 150 gm (100 + 50).

•It may take a few more steps to exactly balance the mass of your object.

•Keep using the procedure: add the next largest unit and that is too much remove that unit and replace it with the next largest unit.

•When the object and the mass units are balanced, line up the mass units from the largest to smallest.

•Total the number of grams in the mass units and bingo you know the mass of the object.

In the left pan of the balance scale is a quartz crystal. In the yellow pan are the masses that balance the mass of the crystal.

What is the mass of the quartz crystal?

Yes, it would be

100 + 50 + 10 = 160 g

In the left pan of the balance scale is a gourd. In the yellow pan are the masses that balance the mass of the gourd.

What is the mass of the gourd?

Yes, it is 10 + 5 + 2 + 1 = 18 g

photo courtesy NASA

Study science and when you grow up you may get a chance to go to the moon where:

you can leap high and weigh less, but don’t forget, your mass will still be the same.