# Calculate Mass, Weight and Gravity

In this worksheet, students will learn the definition of mass and how it differs from weight; and the effect of the gravitational force of the Earth is investigated.

Key stage:  KS 4

Difficulty level:

### QUESTION 1 of 10

Ever thought about how much you weigh? What if I told you you could lose weight by going into space - in fact, you would weigh nothing at all if you were in space. Want to put on weight? Why not just take a trip to Jupiter - you would weigh 23 times more than you weigh on the earth! Trouble is that when you get back to Earth, your weight will be back to normal, so it's not a quick way to change your body shape... There is obviously something weird going on here, and it is with the use of the word weight. In science, it doesn't mean what you think it means - let's take a look at it in more detail.

Mass is the amount of matter in an object. Weight is a force acting on that matter. Weight is the result of gravity that attracts objects towards the centre of the Earth.

The strength of the weight as a force depends on the strength of the gravitational field around the Earth and other planets. The formula that shows the relation between mass, weight and gravitational field strength is:

weight  =  mass  ×  gravitational field strength

Weight is measured in Newtons (N), mass in kg and the gravitational field strength on Earth is 10 N/kg. On the moon it is only 1.6 N/kg.

Gravity is very important because it keeps the Earth's atmosphere in place. It also secures the orbit of the planets around the Sun and keeps galaxies together. Tides are a result of the gravitational pull between the Earth and the moon, as you can see in this diagram.

Black holes have an extremely high gravitational pull, so nothing can escape them.

Now on to some questions!

Choose the right definition of mass.

The strength of gravity in an object

The amount of matter in an object

How heavy an object is

What is weight?

Mass

Gravity

A force

Why is there such a force as weight?

Because of Earth's magnetic field

Because of mass

Because of gravity

Calculate the weight of a 1 kg book on Earth.

1 N

10 N

100 N

Calculate the weight of the same 1 kg book on the moon.

1.6 N

1.6 kg

1.6 N/kg

Calculate the mass of an object if its weight on Earth is 100 N.

1000 kg

100 kg

10 kg

What is the gravitational field of planet X if a 100 kg object weighs 5000 N there?

500,000 N/kg

500 N/kg

50 N/kg

Name a phenomenon that occurs due to gravity on Earth.

The sea

Tides

Space rockets

Name a phenomenon that occurs in space due to gravity.

Black holes

Meteorites

Stars

How is gravity vital to life on Earth?

We cannot escape Earth

The atmosphere stays in its place

Gravity keeps galaxies together

• Question 1

Choose the right definition of mass.

The amount of matter in an object
EDDIE SAYS
Okay, did you get this one? It is a pretty crucial definition to know so make sure you learn it! Mass is the amount of matter in an object. The mass of something doesn't change no matter where it is.
• Question 2

What is weight?

A force
EDDIE SAYS
It's hard to define weight but, hopefully, you were able to eliminate the other two options here to end up with the correct answer. Weight is a force. It depends on how much gravity is pulling your mass down, so in space it is zero and on Jupiter it is 23 times what it is on earth.
• Question 3

Why is there such a force as weight?

Because of gravity
EDDIE SAYS
Weight is the result of gravity. It is a measurement of how much gravity is pulling you into the object that you are using to weigh yourself.
• Question 4

Calculate the weight of a 1 kg book on Earth.

10 N
EDDIE SAYS
Right, this is a simple calculation based on that wonderful equation given in the Introduction: weight = mass x Earth's gravitational field strength Earth's gravitational field strength is 10 N/kg and the mass = 1 kg So, weight = 1 x 10 = 10 N
• Question 5

Calculate the weight of the same 1 kg book on the moon.

1.6 N
EDDIE SAYS
So, we use the same equation as in the previous question but include the moon's gravitational field strength this time, which is 1.6 N/kg. weight = mass x moon's gravitational field strength weight = 1 x 1.6 = 1.6 N Did you choose 1.6 kg instead of N? Remember that in these calculations, the mass is in kilograms but the weight is measured in Newtons.
• Question 6

Calculate the mass of an object if its weight on Earth is 100 N.

10 kg
EDDIE SAYS
Are you getting the hang of this equation now? weight = mass x Earth's gravitational field strength This time, you need to find the mass so you need to rearrange the equation: mass = weight ÷ gravity mass = 100 ÷ 10 = 10 kg
• Question 7

What is the gravitational field of planet X if a 100 kg object weighs 5000 N there?

50 N/kg
EDDIE SAYS
Once again, we need to use our equation: weight = mass x gravitational field strength This time we need to find the gravitational field strength, so we rearrange the equation: gravitational field strength = weight ÷ mass gravitational field strength of planet X = 5,000 ÷ 100 = 50 N/kg
• Question 8

Name a phenomenon that occurs due to gravity on Earth.

Tides
EDDIE SAYS
Tides are the result of the gravitational pull between the Earth and the moon. The moon pulls the seas up and that makes the high and low tides. When the moon lets the sea go, it is in between.
• Question 9

Name a phenomenon that occurs in space due to gravity.

Black holes
EDDIE SAYS
Black holes have an extreme gravitational pull - therefore, nothing can escape them. We have only just been able to photograph them because not even light can escape them - hence the term black.
• Question 10

How is gravity vital to life on Earth?

The atmosphere stays in its place
EDDIE SAYS
Gravity is vital to life on Earth because it keeps the atmosphere in its place. No gravity would mean no atmosphere, no oxygen, no life! Do you feel more confident with the difference between mass, weight and gravity now? It is a hard concept to grasp so don't hesitate to go back to look at the definition once more and maybe do a little more practice on those calculations.
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