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. For practical purposes, the mass and weight of an object on earth are the same and the terms are used interchangeably,
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 plasticene 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.
- Instead of using stations where students are left to work with partners, convert the stations to daily sessions, offering a more supported experience.
The objects weighed in unit can be selected to suit the interests and experiences 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, berries or shells).
- Station 1: Soft drink cans, shoe box lids (cut to about 10 cm in width), plasticene, small toys (plastic vehicles and animals from BSM)
- Station 2: Plasticene, 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.
- First make a see-saw.
Stop the soft drink can from rolling by fixing it to the table with tape or put plasticene rolls on each side.
- Now see if the students can balance the lid on the can when it is empty.
- Now use the cars and animals to see if you can find things that make the see-saw balance.
- Draw a picture to show some of the things that 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 plasticene or play dough to find that changes in an object’s shape does not change its weight.
- Give each student a ball of plasticene. 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.
- If they are different ask them to make them the same by removing some of the play dough.
- Ask the students to make a cat using their plasticene.
Will your cats be the same weight? Why /Why not?
Check on the balance scales.
- Ask the students to remake their "cat" 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 of what they found out.
Station Three: What balances Freddy Frog?
In this station the students experiment to find items that balance Freddy Frog (or an alternative object). 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.
- Ask that the students put their solutions with their name on the chart paper.
- 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.
- 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.
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.