Heavy for its size: what is it made of?
Pupils name the materials that same-sized objects are made from, predict which feel heaviest, check with a balance, and learn why meteorite hunters notice a stone that feels too heavy for its size.
- Tell the difference between an object and the material it is made from.
- Name wood, plastic, metal and rock, and compare objects of the same size by how heavy they feel.
- Use a balance to check a prediction, and say that metal objects usually feel heavier than wooden or plastic ones of the same size.
National Curriculum links
- Year 1, Everyday materials: distinguish between an object and the material from which it is made.
- Year 1, Everyday materials: identify and name a variety of everyday materials, including wood, plastic, glass, metal, water and rock.
- Year 1, Everyday materials: compare and group together a variety of everyday materials on the basis of their simple physical properties.
- Key Stage 1, working scientifically: observing closely using simple equipment; performing simple tests; identifying and classifying.
Key vocabulary
- object
- material
- metal
- wood
- plastic
- rock
- heavy
- light
- balance
- meteorite
Resources
- For each group, five objects of roughly the same size (about as big as a matchbox): a wooden block, a plastic toy brick, a large steel nut or bolt, a smooth pebble and a ball of cotton wool.
- A bucket balance (pan balance) for each group.
- Two sorting hoops labelled "heavy for its size" and "light for its size".
- Two identical closed paper bags for the starter, one holding a pebble and one holding cotton wool.
- Pictures of iron meteorites such as Hoba and Willamette on a screen, and a real iron meteorite if your school or a museum loan box can provide one.
- The worksheet, one per pupil.
Background for the teacher
Two objects of the same size can weigh very different amounts because some materials pack much more matter into the same space. Older pupils will call this density; Year 1 pupils only need the idea "heavy for its size".
Iron is about eight times as heavy as water for the same volume, most Earth rocks are about two and a half to three times as heavy, and many woods are lighter than water, which is why they float. Iron meteorites are almost all iron–nickel metal, so they feel astonishingly heavy in the hand. Stony meteorites often contain small grains of metal too, so they usually feel a little heavier than an ordinary pebble of the same size. Meteorite hunters use this as one of their first clues, alongside a dark crust and a magnet.
The comparison only works for objects of the same size. A large cushion can weigh more than a small pebble, so set out objects that match in size, and if a plastic brick is hollow, say so: it is light partly because it is full of air.
Lesson plan
Starter 10 minutes
Hold up the two closed paper bags and ask: which one is heavier? How could we find out without looking? Let a few children hold one bag in each hand, then reveal the pebble and the cotton wool.
Hold up a spoon and ask: is "spoon" the name of the object or the material? Agree that spoon is the object and metal, wood or plastic is the material. Repeat with a cup and a ruler.
Main 25 minutes
Give each group the five objects. Children name each object and its material, then hold two at a time, one in each hand, and decide which feels heavier. They record their guesses on the worksheet.
Show the balance: put one object in each bucket, and the side that goes down holds the heavier object. Groups check their guesses pair by pair, then sort the objects into the two hoops.
Bring the class together. In most groups the metal nut is the heaviest for its size, then the pebble, with wood, plastic and cotton wool lighter. Accept what the balance showed even if a group's wood and plastic swapped places: the balance is the evidence.
Show the pictures of Hoba and Willamette, two famous iron meteorites, and explain that space rocks made of metal feel far heavier than an ordinary stone of the same size. If you have a real meteorite, let children hold it over a soft tray.
Plenary 10 minutes
Quick-fire thumbs up or down: "A metal key is heavier than a plastic key the same size." "A balance goes down on the lighter side." "Cotton wool is a material."
Each child tells a partner one object, the material it is made from, and whether it is heavy or light for its size.
Differentiation
Compare two objects at a time with an adult, and use picture cards with the material names to label them.
Compare all five objects in pairs with the balance and sort them into the hoops.
Put all five in order from heaviest to lightest for their size, and explain why a big cushion can weigh more than a small pebble even though cushion stuffing is light for its size.
Safety and risk assessment
Check these points against your employer's risk assessment and your school's policies before the lesson.
| Hazard | How to control it |
|---|---|
| Small objects could be swallowed | Use objects larger than a child's mouth; count them out and back in. |
| Heavy metal objects dropped on toes | Keep objects on the table or over the balance; nobody carries them around the room. |
| Germs and dust on rocks and meteorites | Wash hands after handling. Nobody licks or tastes any rock or meteorite. |
| Damage to a real meteorite | An adult hands it over a soft tray, one child at a time, and it is never dropped, scratched or tested with anything. |
Assessment questions with answers
- Is "cup" the name of an object or a material?Answer: An object. The material might be plastic, glass or china.
- A wooden block and a metal block are the same size. Which feels heavier?Answer: The metal block.
- How can you check which of two objects is heavier without just guessing?Answer: Put one in each side of a balance. The side that goes down holds the heavier object.
- Why must we compare objects that are the same size?Answer: A bigger object can weigh more just because it is bigger. Comparing same-sized objects shows which material is heavier for its size.
- A meteorite hunter picks up a stone that feels much heavier than other stones its size. What might be inside it?Answer: Metal, such as iron.
Homework
With a grown-up, find three things at home that are about the same size but made of different materials. Hold them one at a time and draw them in order from heaviest to lightest. Write or say what each one is made of.
Answer guidance: Answers will vary. Metal objects usually come first; check that each drawing is labelled with a material, not an object name.
Use with these pages
These eight lessons are a free starter pack, written specially for this site. The full set of 25 lesson plans, with worksheets, end-of-unit tests and mark schemes, is in the Corvanelle book Teaching Meteorites. The lessons in the book are different lessons, so the starter pack and the book work together rather than repeating each other.