In this lesson we are introducing weight and how to compare the weight of two objects.

The weight of an object is a force that pushes downwards. You can feel the weight of lots of different objects when you hold them. It is the reason we find it difficult to lift some objects at all.

Below is a set of scales. Scales can be used to compare the weights of two objects.

We place a mass at one end of the scale. There is nothing on the other end.

The weight of the mass pushes down on this end of the scale and so this left side moves downwards.

This causes the other side to rise upwards.

When teaching weight to children, it can be helpful to have a physical set of scales to play with, so that your child can experience how it works for themself.

We do not need a large mass to push the scale downwards.

Since there is nothing at the one end, if anything is placed on the other end, it will push down on the scale.

We will put a pencil on the scale at one end.

The pencil pushes down on the left hand side of the scale, causing this side to move downward.

In the example below, we will place two objects on the scale.We will compare the weight of a tennis ball and a feather.

To compare the weight of two objects, they need to be on separate ends of the scales.

The side with the tennis ball moves downwards.

This has happened because the tennis ball pushes down on the scales more than the feather does.

We say that the tennis ball is heavier than the feather.

This means that is is more difficult to lift up than a feather.

The opposite way to say this is to say that the feather is lighter than the tennis ball.

This means that the feather is easier to lift up than the tennis ball.

When teaching weight and mass to children, we can consider them as being very similar, using the words almost interchangeably. However, the mass of an object measures how much matter is inside the object.

You can explain this with an empty and full box. The full box will be heavier and more difficult to move than the empty box because it has more matter inside it.

The weight of the tennis ball pushes downwards more than the weight of the feather. The mass of the tennis ball means that it is more difficult to move in any direction. We can try blowing a tennis ball and a feather and see that it is much easier to move the feather.

In these introductory examples, we simply need to decide which object is heavier by looking at the scales to see which side has been pushed down.

In this next example we will compare the weight of a book and a leaf.

The side with the book moves down causing the side with the leaf to move up.

The book is lower on the scale than the leaf.

Therefore, the book is heavier than the leaf.

And the leaf is lighter than the book.

Remember that the leaf only moves upwards because the book moves downwards pushing the leaf side upwards.

Some children may have the misconception that the leaf being light causes the scales to move upwards. The best way to overcome this misconception is to remove the book and see what happens when the leaf is on the scales alone.

If the leaf is on the scales alone with no book, then the leaf will push its side downwards. It does not cause the scale to rise up. Objects’ weights can only push downwards.

An object being ‘light’ only means that it is not ‘heavy’. Sometimes this word can confuse children who may associate it with balloons which actually may have an upwards force.

Objects always push downwards with their weight. Even feathers and leaves have a weight which pushes downwards.

In this last example, we compare the weights of a carrot and a strawberry.

The carrot pushes this side downwards, causing the strawberry side to move upwards.

The carrot has a larger weight than the strawberry.

The carrot is heavier than the strawberry.

The strawberry is lighter than the carrot.

When teaching and introducing weight to children it is important to consider real life examples so that the child can relate their understanding to what they have already experienced.

Simply holding two objects in each hand can be a way to feel and compare their weights.

If you do not have scales to use in this lesson, you can simply hold the objects and feel which is harder to lift.

Asking your child questions such as, “What do you think is heavier…?” or, “Why can’t you lift…?” will help them realise that they already have an understanding of some aspects of weight. They will probably already know that some objects are heavy and cannot be lifted.

Sometimes they may believe that an object’s weight is linked completely to its size.

This is true if the objects are the same material. For example, a larger rock will be heavier than a smaller rock or a larger person will be heavier than a smaller human. However it is important to explain that this is not always true when comparing different materials.

A small tennis ball may be heavier than an inflatable beach ball or you may have some toys that you can use to show this.