Floating and sinking activities are great and can involve a huge range of materials.
Fill your water tray 1/3 full ~ if you have chance to use a deeper fishtank or terrarium ~ this would be much better for visually following the sinking objects ~ and even better if you can take the activity outside
Activity idea for an Instant float or sink game
Objects that float and Objects that sink
Cork ~ pieces of or bottle stoppers
Plastic lids
Lego bricks or Duplo
Feathers
paper
Wax ~ slice some from a candle
Glitter
Play boats
Grass
Flower heads
Bubbles
Chunky Chalks
Bath sponges
Marbles
Ice
Jelly
Large paper clips
Bar of soap
Pencil
Ruler
Spoon
Pumice Stone
Conkers
Sea shells
pebbles, stones, brick
Cotton reels
Rice, lentils dried peas
Keys
Padlocks
Metal washers
Coins
A Christmas, Winter or Yule time float and sink:
Baubles
Tinsel
Glitter
Fir cones
Dried fruit slices
Ribbon and Bows
Christmas shaped bath sponges
Socks, ties & hankerchiefs
lol
Mittens, Gloves
Nuts
Currants, Sultanas, Raisins
Bead decorations
Blocks of ice (add glittery things to the water before freezing)
To demonstrate the word and action ~ 'Float'
Place your objects into an empty bowl and slowly fill it with water .. the children will soon see that 'float' also means to be 'lifted' as the water rises.
Explain that this is because the item is light and can rest on the surface of the water.
The heavy objects will remain on the bottom.
Reverse the activity for demonstrating 'Sink'
and explain that when you place objects into an already filled container the heavy ones 'fall through the water to the bottom.