Teaching Weight

The difference between mass and weight

Before we start thinking about teaching weight, teachers need to understand the difference between mass and weight.  Children often confuse mass and weight and this causes some of the difficulties that we see in the classroom. The mass of an object is the amount of matter in an object. The mass of an object never changes. However, the weight of an object is a measurement of how much an object is affected by gravity. So, if we move an object to a place where there is less gravity (for example, on the moon), then the weight of the object changes. 

Weight is a tricky concept: what makes it difficult to understand?

Before thinking about teaching weight, it is good to be aware of the difficulties and misconceptions that young pupils have about weight. 

Difficulty  #1: You can’t see weight

The difficulty understanding weight is that it is not an attribute that can be seen.  Imagine showing a beach ball to pupils - the mass of a large beach ball is visible but the weight is not visible. That is why some pupils are surprised when they handle a large beach ball and find that it is light. We often think ourselves that bigger objects are heavier; and in a lot of situations this is true - but not always!  Ensuring that pupils have opportunities to handle, lift and drag object are essential to developing understanding. Another fun way to help is to have pupils look at this great video from the sesame street archives. Not only is it fun for younger pupils to watch but the actions of the character Telly really convey the idea of something being really heavy!  

Teaching tip! The song in this video might be a nice way to start your maths lesson each morning and link maths with music in the early years.

 

Difficulty #2: Conservation of mass

As mentioned earlier, young students are influenced by what they see and can be easily deceived by the shape or the size of an object. Another related problem is conservation of mass. Pupils who do not yet conserve the property of mass will think that if the shape of an object changes so does its mass. We know that if we change our own shape (roll up in a ball, stretch, or stand on our head) that our mass remains the same. However, young children do not understand this i.e. they do not conserve mass.

Look at the following video that highlights the misconception – start watching the video at 2:17 and end at 3:17.

 

 

The Zipline Balancer: helping us think about teaching weight

We use the same 5-step sequence for teaching weight as we did for teaching length over the past 2 weeks. To help you imagine teaching weight in the early years you should first download or print the assigned reading. This reading describes activities we designed to teach the concept of weight to five and six year old children in a local Limerick school. As you go through the remaining session we’ll refer you to parts of the reading, which shows how to teach weight in the classroom.

Step 1: Number free comparison

Step 1: Number Free Comparison [Comparing and Ordering]

During step1, number free comparison, which may span a week of teaching, we help pupils understand the attribute of weight and develop an understanding of heavy, light, heavier, lighter and so on. The following two activities are important to developing this understanding.

 

ACTIVITY #1: Understanding balancing

Young children know what it means if something balances. Referring to their experiences of a see saw or informal play activities where they try to balance two objects is a meaningful way to introduce the concept of weight. 

 

Over to you!  Read the 'the zipline balancer' (end of page 1 and all of page 2) to see how we discussed with children what happens when objects balance. Notice how we started by asking what their experiences of balancing are and weaved in the context of a ‘zipline balancer’. For pupils who do not have experiences of zipwires, we showed images and a video or a 2-person ski lift to support them in accessing the balancing analogy.

Now, checking your understanding:

·        Why did we think it was important to include the images in figures 1a and 1b in the reading?

·        What real life experience with balancing do you think Fiadh is recalling?

·        What do you think about our teaching decision to have children compare the (smaller but heavier) elephant with the (larger but lighter) horse? What misconception were we hoping to address?

·        How you would respond to Fiadh’s explanation at the top of page 3. What does it tell us about her understanding of weight?

·        Present pairs of objects to pupils

·        Have pupils estimate first (by hand weighing) which is heavy / light

·        Pupils pass objects around and confirm which one they believe is heavier.

·        The two-pan balance can then be introduced 

·        Teacher demonstration is necessary to show how to use the balance.

·        Pupils need to discover that the lower pan contains the heavier object and the higher pan contains the lighter object.

·        It may be helpful to make reference to experiences with a ‘see-saw’

ACTIVITY #2: Comparing weights

Comparing the weight of objects is very important and in the early years we focus on number free comparison. The following sequence could take place over 4-5 lessons to ensure pupils get many experiences handling objects:

See these images of 2-pan balances and how you might explain their use:

 

Over to you! Read pages 3 and 4 to see how linked all the hand weighing and 2-pan balance activities are to our ‘zip line balancer’ context. 

Teacher demonstration was used to model how to hand weigh and how to use the two pan balancer. We also focused on having children predict first and then weigh. 

 

Now, check your understanding:

·        What would you do to support Donagh gain more experience with developing weight vocabulary?

·        Which pupil (Jack, Fiadh, Ethan) has the most sophisticated understanding of weight?

·        Which pupil shares some of the difficulties experienced by Donagh? 

·        Look at the two questions the teacher asks when working with Maria and Theo. What is the purpose of this questioning?

 

Video insight!

Look at this 3-minute video of an American kindergarten child describing his understanding of heavy and light. He predicts, tests and explains what happens. Notice the excellent teacher questioning and how she constantly encourages the child to explain his reasoning. Also notice how excited the child is when handling materials and using the 2-pan balance. Isn’t it interesting how the child describes the same weight objects as occupying ‘the same up’ on the scales!

Step 2: Non standard

Step 2: Measuring with non standard units

At this stage, pupils measure the weight of an object using non-standard units. This allows them to assign a number to the weight of the object (e.g. the pencil weighs 5 marbles). Provide many opportunities, spanning several lessons or weeks, to use 2-pan balances and weigh objects using non-standard units. Good examples of materials to use as non standard units are objects that are the same size and weight such as unifix cubes, blocks and marbles. 

A teacher might first do this as part of a whole class activity:

·        Allow pupils to hold the object e.g. toy car

·        Have pupils make an estimate by asking ‘How many marbles will it take to balance the car?’

·        Then place car on one side of the balance

·        Add marbles one-by-one, counting them, until the car is balanced 

·        Refer back to the estimates

·        Then allow pupils work in groups and practice weighting with different objects (using blocks/marbles to balance).

 

Over to you! Read page 5 which describes children measuring the animals using unifix cubes as the non standard unit. Notice how we posed the problem about Nemo the fish to motivate pupils to want to measure.  

Notice also in the reading that we also have pupils record their estimates and measurements. Here are some images that show this process.

 

Now, CHECK YOUR UNDERSTANDING:

·        Why do we have pupils estimate first and then measure?

Steps 3 & 4: Create the need for and use of standard units

Moving into first class we want children to see the need for using a standard unit of weight. Just like when speaking about length, we need children to realise that in order to communicate measurements we need a universal measurement. Thus, our goals are to provide them with experiences of estimating, measuring and recording weight using standard unit measures such as the kilogram and solve simple problems

 

Some activities to develop understanding of the kilogram

·        Have pupils check labels of common household items to see if they are greater than or less than 1kg.

·        Provide pupils with a model of 1kg so that they can get a sense of what it feels like. If you do not have commercial weights, you can make your own using common household items.

·        Allow children to hand weigh to predict if the food item is greater than (>), less than (<) or equal to 1kg

·        Check their estimates using the 2 pan balance

·        Explore and discuss instances when objects or substances weigh 1 kg vary greatly in size  (e.g. 1 kg of peas, flour, beads, etc.).

 

Over the subsequent school years introduce the gramme using the same procedure as we use for the kilogram. Situate all activities in engaging, hands-on, real life scenarios. The following images have examples of many contexts you might use – although you can probably come up with many more! 

 

Using literature to support understandings of weight

There are many lovely children’s books, which you can use to support your teaching of weight. Some of them are specifically designed for teaching weight, however, you can also use context from familiar storybooks (such as ‘Goldilocks and the three bears’).  

One story we recommend is ‘Just a little bit’ by Anne Tompert. we have it available in the MIC library but here is a video of a teacher reading the story. Read the book or watch the video and answer this: Why do you think we have recommended this story?

Video: https://youtu.be/eDszglqnb58

 

If using this book to introduce children to weight concepts, consider the following teaching tips:

•  Encourage children to talk about their own experiences with seesaws by asking: “What happened when you sat on the seesaw by yourself?” “What happened when your friend got on the other side?” How does it work?

•  Compare the sizes and weights of the various animals (heavy, light, big, small; heavier, lighter, bigger, smaller).

– “Which animal looks bigger—the bear or the monkey?”

– “Which animal do you think is lighter—the lion or the ostrich?”

•  Compare the collective weight of the animals on the mouse’s side of the seesaw to the weight of the elephant.

– “How can you tell if the elephant weighs more than the mouse, giraffe, and zebra all put together?”

•  Ask the children to predict what will happen as each friend joins the mouse on his side of the seesaw; “What do you think will happen when the bear gets on?”

•  Ask the children to give explanations for why it's not working when different animals get on the seesaw.

– “Why didn’t the seesaw go down? What should the animals do now?”

 

Step 5: Create the need for a smaller unit of measurement

Knowing that an item is >, < 1kg, ½ kg, ¼ kg still does not answer the question – ‘how heavy is it?’ More precision needed for various everyday activities.

Measuring Using Grams (g)

·        Provide models of 1g e.g. cubes, compare bears (check)

·        Allow children to get a feel for what 1g feels like and estimate and measure appropriately using the 2-pan balance initially (iterating the unit).

Results: classroom activity Measuring the objects listed below with a balance scale and grams
Object	Guess	Grams
1 red teddy	12g	10g
1 green teddy	9g	7g
1 elephant	11g	8.5g
1 dinosaur	10g	8.5g

 

Select and Use Appropriate Instruments

Measuring….	Instrument	Unit: mg/g/kg/tonne
Flour for a cake
Weight of suitcase
Boxer weighing in before a match
Weight of tablets
Your own weight

Renaming Units of Weight

Remember: Whenever possible, students should develop and apply formulas meaningfully through investigation rather than simply memorise them.

Everyday Item	g	kg (fraction form)	kg (decimal form)
Cornflakes	750g
Butter			0.454g
Bag of flour	1,000g
Bag of crisps
Bag of coal			40.0kg
Biscuits
Slice Pan			0.8kg
Large bag of potatoes			10kg

 

 

Step 5: Create the need for a larger unit of measurement

·        Reality that some items are so heavy, they are thousands of kilograms

o   E.g. weight of cattle going to the market, sand in a lorry delivered to a building site

·        Once you have 1000kg, this is called 1 tonne

·        Things like cars, trucks, cattle meal, coal, cargo containers are weighed in tonnes

 

Tutorial Tasks Exploring Weight Concepts

Task 1: Target Board Activities

How to use Target Boards

a)      Using the numbers in the grid, students have to try and reach that target, or

b)     Find me another way of saying ……

c)      Mystery Number (give clues one at a time) my mystery number is less than 2kg, more than ½kg…

Your Task

·        Write 5-7 questions you could present to 4th class children with this target board

·        What challenges might you face using the target board for weight?

·        How might you modify this target board?

·        What contexts could you use to support work with the target board?

Sample Questions for Target Boards

Task 2: Exploring Weighing Scales

With your instrument: pan balance, digital scales, analogue scales, spring balance

·        Explore the intervals that your instrument can measure in.

·        GSM Arena recently published their poll results which found that the ideal weight for a phone is between 140g and 170g.

o   Estimate and measure the weight of your mobile phones using your instrument. Does your mobile phone weight fall within this range?

·        Identify the advantages and disadvantages associated with your instrument.

Task 3: Postage Rates

You are sending a parcel to family member for Christmas:

·        Choose where you are going to send it?

·        How quickly?

o   What options do I have?

·        What am I putting in it?

o   Select and find the weight of five items you would send.

·        What is the total weight of your parcel?

How much will it cost to send?