Making Benchmarks - Mass
In this unit we will explore the idea of having Benchmarks of 1 kilogram and 1/2 kilogram or 500 grams to aid in estimating the mass of given objects.
use objects of 1kg mass to estimate the mass of other objects
discuss the need for having and using standard measures of mass
make sensible estimates about the mass of given objects
explain the meaning of metric prefix terminology (e.g kilo)
It is difficult to estimate the mass of individual items. Try picking up a schoolbag and estimating it’s mass. It is something most people aren’t that good at because we haven’t had much practice or we don’t have the same ‘onboard’ means in which to benchmark like in length e.g fingertip to shoulder – 1 metre. Students need to develop personal benchmarks with which to measure various objects in their daily lives. Their personal benchmarks need to gradually relate more to standard measures such as 1 kilogram or 500 grams.
Students also need to be provided with opportunities and experiences to explore the connections between;
- kilograms and grams
To support the understandings of these connections students will explore the language of measurement including prefixes such as kilo. The ultimate aim is for students to be able to choose appropriately from a range of strategies including estimation, knowledge of benchmarks, and knowledge of standards measures in order to approach various measuring tasks with confidence and accuracy.
It should be mentioned that mass and weight are not the same thing. Mass is the measure of the inertia of an object – its amount of response to a force applied to it. If the same force is applied to several objects, those with a smaller mass will be affected the most. Mass is not proportional to volume – a piece of lead has a far greater mass than a similar sized piece of foam plastic. We judge an object’s mass by weighing it – the weight of an object is it’s mass under the force of gravity. Because gravity is close to constant on earth, this gives a good measure of mass. If an object were taken to the moon, it’s mass would be the same as on earth, but its weight would be considerably less because the gravity on the moon is far weaker than on earth.
Getting Started
Begin by asking students to bring in their school bag. Pose the question - Who has the heaviest bag to carry to school and who carries the lightest bag to school?
- Begin by selecting 5 or 6 bags from around the class – it is important to select bags of various sizes and shapes to discuss that biggest doesn’t necessarily mean heaviest to further explore the idea of conservation.
- How are we going to go about ordering these bags from the lightest to the heaviest bag to answer our question?
- Gather suggested solution strategies then trial strategies to establish an effective way to order the bags by weight.
- Group students in groups of 5-6 with their bags. Ask each group to order their bags from least to most heavy.
- Share the techniques and strategies used by each group to order the bags.
- Ask 2 groups to pair up to combine their bags on one continuum of least to most heavy.
Exploring
The following activities are to provide students with experiences to compare weights of different objects and to create a benchmark of what a kilogram feels like.
- Make available a 1kg weight for students to use to give them the ‘feel’ of a kilogram.
- Seat the class in a circle around a variety of items from around the room, from your kitchen etc. Ensure items like 1kg bag of sugar or a 1 litre container of milk or water are included in the items as such items will become useful benchmarks.
- On large sheets of paper draw and label the following buckets.
- Ask individuals to select an item and place it in the most appropriate bucket. Before each item is placed in the bucket it would be a good idea to pass the object around the circle for students to feel the mass of each object. This activity could be carried out in smaller groups if necessary to give individuals more hands-on experience.
Homelinks
- Ask students to locate items from around their home that they believe would make good benchmarks for 1kg. Ask them to bring along an object that they think has a one kilogram mass.
Session 3
- Ask individuals to bring their 1 kg benchmark items to the mat.
- Using scales check the actual measurement of each of the around 1kg items to see how close they are to 1kg.
- Give students 5-10 minutes to rove around the circle and hold one another’s item.
- Ask students to discuss which of the benchmarks are the most useful. For example, objects which you don’t usually pick up are not particularly good benchmarks as you will not be familiar with their mass.
- Either individually or in small groups give students a plastic bag and ask them to put one kilogram of something in it. You may prefer to do this activity outside in the sand area (using sand to make a kilogram) or you may do it inside and suggest a range of items that could be used to make one kilogram.
- Weigh the bags and discuss why they are not all exactly one kilogram. Compare them to the benchmarks.
- Class discussion needs to now focus on how many grams are there in one kilogram? The following types of questions can be asked to explore the connections between grams and kilograms.
What does kilo stand for?
How many kilograms is 2000g?
How many grams in 1.5 kg?
Session 4
- Organise students into groups of 2-4 and ask each group to select one of the near 1 kg items that were identified from the previous day. This will be used as the group’s benchmark to measure various other items around the room.
- Group members take turns to be blindfolded. In one hand they hold the bench mark and in the other hand they are given another item. The task is to estimate the mass of the mystery item by comparing its mass with the benchmark item.
The blindfolded individual verbally announces their estimate and a recorder records the estimation. The non-blindfolded individuals can also estimate the mass of the mystery object. - After each estimate students then use scales to measure the item’s mass. The comparison can then be made between the actual mass and the estimated mass.
The process can be repeated for each group member. - This could be turned into a game in that the individuals who estimate within 100grams earn themselves a point. The first group member to earn four points is the winner.
Reflection
- Bring this unit to a conclusion by asking students to share the benchmarks they are going to use for 1kg.
- List the various benchmarks on a large sheet of paper to be displayed as a reference.
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Share the various strategies and techniques students have developed to establish near estimates for objects they are asked to weight.
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Ask students to think about other possible accessible items that could be used as benchmarks to measure items that are less than 1kg in mass. How many grams does your average can of baked beans weigh? How much does a 50c piece weigh?
Dear Family,
This week children will be asked to bring items to school that they think would be useful benchmark for 1kg.
Ask your child how much they estimate some items around the house to weigh? Ask them to share their own built in benchmarks for estimating the mass of different items around the home.
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