This unit involves the students directly comparing the weight (mass) of two or more objects.
- Compare two objects by weight.
- Order three or more objects by weight.
- Describe the weight of objects using comparative language, for example, heavier, lighter.
Weight is a measure of the force of gravity on an object. Mass is the amount of matter in an object and a measure of the force needed to accelerate it. This means that the mass of the object on the moon is the same as its mass on earth, but its weight is lighter on the moon. In a science context, weight is measured in Newtons (N), and mass is measured in kilograms (kg), grams (g), and milligrams (mg). However, these terms are often used interchangeably. For practical purposes, the language commonly used to measure weight and mass in everyday life is kilograms, and grams. Choose one term (e.g.weight or mass) and use it consistently with your students.
An important early goal in measurement is for students to understand the attribute they are going to measure. Comparison activities help students develop an understanding of the attribute that is being measured. In the case of mass, the most personal experience is comparing the weights of two objects by holding one in each hand and feeling which has the greatest downward pull. This personal experience can then be transferred to the use of balance and spring scales.
Young students are influenced by what they see. The shape or the size of an object can easily deceive them. For example, students who do not yet conserve the property of mass will think that if the shape of an object changes then so does its mass. In one of the stations, in this unit, the students change the shape of a piece of plasticine and then weigh it to see that the weight has stayed the same.
The learning opportunities in this unit can be differentiated by providing or removing support to students and by varying the task requirements. Ways to provide more support include:
- comparing the weight of objects using hands and outstretched arms (as described above) to further develop a student’s conceptual understanding of weight
- modelling the tasks to be done at each station
- providing visual and written instructions for the tasks to be done at each station
- instead of using stations where students are left to work with partners, convert the stations to daily sessions, offering a more supported experience.
- providing opportunities for students to work in flexible, multi-level pairs, groups and as individuals.
Te reo Māori vocabulary terms such as taimāmā (light), taumaha (heavy), ine-taumaha (scale for measuring weight) and maihea (weight) could be introduced in this unit and used throughout other mathematical learning.
The objects weighed in this unit can be selected to suit the interests, experiences and culture of your students. For example, the students could bring small objects from home or objects that they can collect from around the school playground (e.g. stones, cones, twigs or shells). Bringing items from home might offer important opportunities for oral language (i.e. sharing) When students are making objects out of plasticine, students could make objects to reflect their current learning interests (e.g. a snail, if you are learning about minibeasts). Consider how the use of different objects might reinforce learning from other areas, and contribute to a cohesive learning experience across all sessions/stations.
- Station 1: Soft drink cans, shoe box lids (cut to about 10 cm in width), plasticine, small toys (plastic vehicles and animals), shells and rocks
- Station 2: Plasticine, homemade "seesaw"
- Station 3: Balance scales, toys
- Station 4: Balance scales, toys
- Station 5: Hat elastic, bull-dog clip, toys, paper, crayon
Station One: See-saws
In this station we work with a partner to make a see-saw using a soft-drink can and a shoe box lid. We then use the see-saw to find objects that are the same weight.
- Discuss what it means to weigh an item. Students might suggest that it means to find out how heavy something is, or whether one item is heavier than another. Discuss what tools we can use to measure how heavy or light something is, and times when we might measure the weight of different items (e.g. baking, cooking, collecting mātaitai/shellfish). List down the contexts suggested by students. Students might also suggest words that are used to talk about the weight of things in their home language (e.g. taumaha/heavy, taimāmā/light). Record these prompt their usage throughout the sessions.
- Explain that the class is going to use a see-saw to find objects that are the same weight.
- First make a see-saw.
Stop the soft drink can from rolling by fixing it to the table with tape or by putting plasticine rolls on each side.
- See if the students can balance the lid on the can when it is empty.
- Use the cars, animals, shells and rocks to see if you can find things that make the see-saw balance.
- Draw a picture to show some of the things that are balanced.
- As the students work ask questions that focus on the way that things balance
How did you make your see-saw?
What are some things you found that balance? Show me.
Have you ever been on a see-saw? What happens?
Station Two: Weighing balls and worms
In this station the students, in pairs, experiment with plasticine or play dough to find that changes in an object’s shape does not change its weight.
- Give each student a ball of plasticine. Tell them that they need to work with a partner.
- Ask them to check that their "balls" are the same weight by using their see-saws. You may need to model how to use the see-saw. A student could also demonstrate.
- If they are different ask them to make them the same by removing some of the play dough.
- Ask the students to make an object (e.g. a kiwi) using their plasticine.
Will your kiwis be the same weight? Why /Why not?
Check on the balance scales.
- Ask the students to remake their "kiwi" into the longest worm they can.
Whose worm is longest?
Whose worm is heaviest? Check?
Why are they the same weight?
- Ask the students to make their "worm" into different sized balls.
Whose has made the most balls?
Which ball is the heaviest? Check?
If you both put all your balls together on the seesaw what do you think will happen?
What do you notice? Why is the seesaw balanced?
- Ask the students to draw a picture or record what they found out. You could record this on a digital presentation or poster for the whole class to refer back to.
Station Three: What balances Freddy Frog?
In this station the students experiment to find items that balance Freddy Frog (or an alternative object eg Terry Tui). The students paste their solutions onto a class chart.
- Set up the balance scales with Freddy Frog in one of the balance buckets.
- Have a collection of different objects at the table for the students to experiment with, for example, linking cubes, pattern blocks, counters, small toys, buttons, shells, rocks.
- Ask students to put their solutions with their name on the chart paper or record them on a device.
- Ask questions that focus on their use of the balance scale.
What happens on the scales when Freddy is heavier?
Do you think that this "car" will be lighter or heavier? Why do you think that? Were you right?
What are some of the things that you found that were the same weight as Freddy Frog?
In this station we line objects up in order of weight so that we can work out who goes where in our "tower". We need to have the heaviest at the bottom and the lightest at the top. Note this activity can also be taken outside using natural materials.
- Give the students four toys and ask them to put them in order of weight.
- Before using the balance scales ask the students to hold the toys and guess the lightest and heaviest.
- Check guesses with the balance scales.
Were your guesses correct?
Tell me how you put the toys in order?
- Ask the students to find another toy or object, which is lighter than the four toys they have ordered.
Did you find a lighter toy on your first guess?
How did you check your guess?
- Ask them to find another toy or object which is heavier than the 5 they now have ordered. Share their findings with a buddy.
Station Five: Bungees
In this station students use a simple piece of elastic as a bungee and measure how far the elastic stretches to compare the weight of different objects.
- Set up a bungee by tying a piece of elastic onto a bull-clip or a clothes peg. The top of the bungee will need to be attached to something it can hang from, a string suspended tight across the classroom or a metre ruler suspended across two desks would be ideal. There also needs to be a piece of paper behind the bungee, which the students can use to mark how far down the wall the bungee extends
- Have students take one object at a time and attach it to the clip. They then let the objects go, wait till the elastic comes to rest and mark on the paper how far down the object falls.
- Students repeat for all objects and then decide which is heaviest.