Make Things Sink, Then Float

You will need

  • Modelling clay or blue tag
  • Marbles (if you don’t have marbles, use small rocks)
  • Water
  • Glass bowl or a large glass jar

What to do

  1. Fill the glass bowl or jar with water.
  2. Drop the marbles into the water. They quickly sink to the bottom. Roll the clay into a ball and drop it into the water as well.
  3. The clay also sinks like the marbles.
  4. Remove the marbles and the clay ball from the water.
  5. Flatten the clay as much as possible, then shape it to make a boat and place it into the water. Now it floats!
  6. Add one marble as a cargo. The boat settles lower, but still floats.
  7. Add more marbles, one at a time. How many can you add before your boat sinks?

Background

Large ships float on water, even though they are very heavy.  However, a small object like a marble sinks. The mass of the object does not matter. Whether or not an object floats depends on its density and how much water it “displaces”, or pushes aside.

When the clay is shaped like a ball, it does not displace much water and it sinks. When shaped like a boat, the clay has a bigger area and displaces more water which makes it float. When adding your cargo of marbles, the boat settles lower to displace more water and carry the extra mass. When adding too many marbles, the boat will settle below the water line and sink.

This is important for ships. Too much cargo can lower them too close to the water line and make them vulnerable to sinking.

You can watch this experiment as a video here:

Friction with Rice

You will need

  • 1 Plastic bottle (500 ml)
  • Rice (you can still eat it after the experiment)
  • 1 Funnel
  • 1 Chop stick or pencil

What to do

  1. Fill the plastic bottle to the rim with rice. You can use the funnel to help you.
  2. Pick up the bottle and hit its bottom against the table several times. This will compact the rice more and let air escape.
  3. There is some more room in the bottle now. Add more rice until it reaches the rim of the bottle.
  4. Now insert the chop stick or pencil into the rice. Push it down as far as you can.
  5. Take a hold of the chop stick or pencil and lift it up. What happens?

Background

There are different forces acting on the bottle. The force of weight or gravity pulls it down to Earth. When you insert the chop stick or pencil into the rice, there is an additional force of friction between the rice and the chop stick/pencil. The force of friction acts in the opposite direction of gravity.

If the forces of gravity and friction are equal, you are able to pick up the bottle when only holding on to the chop stick/pencil. If forces are equal and act in opposite directions, we say that they are balanced. In this experiment the forces of friction and of gravity are balanced.

You can watch a video of this experiment here:

Build a Compass

You will need

  • Fridge magnet
  • Small bowl
  • Water
  • Needle
  • Piece of cork

What to do

  1. Rub the fridge magnet along the needle several times. You always need to move the magnet in the same direction along the needle. This is done to magnetize the needle and turn it into a temporary magnet.
  2. Gently push the needle through the middle of the cork. Be very careful not to sting yourself.
  3. Fill the bowl with water.
  4. Place needle and cork in the water.
  5. If left alone the needle will align in a North-South direction in the water. Just like a compass needle would.
  6. If you wish you can use the fridge magnet to manipulate the needle and move it in the water.

Background

Rubbing the fridge magnet along the needle magnetizes it and turns it into a temporary magnet. Temporary magnets only remain magnetic for a short amount of time. Permanent magnets like the fridge magnet are always magnetic.

When inserted into the cork and floating in water the needle acts like a compass. Earth has a magnetic field where the poles are located at the North and the South pole. Therefore, the needle will move to align in a North-South direction when floating in water.

You can watch this experiment as a video here:

Make a Sound Gun

You will need

  • Plastic foil
  • Empty toilet roll
  • Scissors
  • Piece of cardboard
  • Thin strip of paper
  • Sharp pencil
  • Rubber band
  • Sticky tape

What to do

  1. Draw around the empty toilet paper roll to make a circle on the piece of cardboard.
  2. Cut out the circle from the cardboard.
  3. Use the sharp end of the pencil to make a tiny hole in the middle of the cardboard circle.
  4. Tape the circle to one end of the tube.
  5. Using the rubber band, fix a piece of plastic foil over the other end.
  6. Cut a thin paper strip, fold it and tape it to the top of the table.
  7. Point the end of the tube with the hole at the paper strip.
  8. If you tap the plastic the strip shakes.

Background

Sound waves are caused by vibrations and detected by our ears. The vibrations of loud sounds can even make things move which is shown by this experiment. Tapping the sound gun makes the paper strip shake.

Sound can even cause avalanches where snow and ice crash down a mountain. Sound waves from a loud noise disturb the snow and start it moving.

You can watch this experiment as a video here:

Home Experiment: Underwater Volcano

You will need:

  • Small bottle
  • Large glass jar
  • Scissors
  • Hot and cold water
  • Red food colouring
  • String

What to do:

  1. Cut a long piece of string.
  2. Tie the string firmly around the neck of the bottle.
  3. Pour cold water into the large glass jar until it is about three quarters full.
  4. Fill the small bottle with hot water. Add food colouring to make the water bright red.
  5. Hold the small bottle by the loop of string. Lower it gently into the jar with cold water.
  6. The hot red water rises from the bottle like smoke from an erupting volcano.

Background:

Hot water is less dense than cold water and always rises to the surface. Cold water floats underneath. This is the reason why the hot red water rises to the surface, making your experiment look like an erupting volcano.

There are deep holes in the ocean floor. Water, heated by rocks deep in the Earth’s crust shoots out of these holes and rises to the surface of the sea. Divers have discovered strange sea creatures that live around these hot-water holes.

You can watch this experiment as a video here:

Home Experiment: Build a Jet

You will need:

  • Long string
  • Sticky tape
  • Balloon
  • Drinking straw
  • Scissors

What to do:

  1. Cut a very long piece of string.
  2. Feed the string through the straw. It must move easily.
  3. Stretch the string across a room and tie its ends to suitable places, for example a door handle or a chair.
  4. Stick two pieces of tape to the straw.
  5. Blow up the balloon. Hold the neck and attach the balloon to the straw. The air must not escape.
  6. Let go of the balloon. It rushes along the thread at high speed.

Background

The balloon produces a jet of air which drives the balloon forwards. It works the same way as jet engines on airplanes. These engines produce powerful jet of air that drives the airplane forwards.

Home Experiment: The Unbreakable Box

You will need

  • One empty match box

What to do

  1. Place the outside box of the match box upright on a table.
  2. Put the inner box upright on top of the outside box.
  3. Try to smash the construction from the top using your fist. What happens?
  4. Now, place only the inner box of the match box upright on a table.
  5. Try to smash the inner box with your fist. What happens now?

Background

When hitting only the inner box, it will smash. However, if inner and outer box are placed on top of each other, they do not smash, but fly off undamaged in a high curve.

The reason is that the inner box can divert pressure to the outer box when both are placed on top of each other. The boxes fly off because their edges are not rigid, but flexible. The elastic energy from the edges is transferred to kinetic energy.

If one box is placed by itself, pressure cannot be diverted and the box is smashed.

You can watch a video for this experiment here:

Home Experiment: Balancing Forces

Background

When objects are not moving or moving at a constant speed, the forces on them are balanced. We are going to try and balance the force of gravity and the force from a hair dryer’s air stream on a table tennis ball.

You will need

  • 1 Table tennis ball
  • 1 Hair dryer

What to do

  1. Point the hair dryer upwards and turn it on.
  2. Carefully place the table tennis ball in the air stream.
  3. The table tennis ball should float in the hair dryer’s air stream.
  4. You might have to play with the strength of the air flow to get things exactly right.
  5. If you get it to work, try to tilt the hair dryer and see how far you can tilt it, before the ball falls off.
  6. When the table tennis ball is floating the forces of the hair drier’s air stream and gravity are exactly balanced.

You can also watch this experiment on YouTube:

Optical Illusion – Home Experiment

Background

Our eyes can only see a certain amount of pictures per second. They are actually quite slow. This is why we cannot see objects that are moving extremely fast. In this experiment we are going to use the slowness of our eyes.

You will need

  • Paper
  • Pencil
  • Pens or colouring pencils to draw a picture
  • Tape
  • Scissors

What to do

  1. From the paper cut two pieces with the same shape and size.
  2. Draw two different pictures on the two pieces of paper that can also go together, for example a rabbit on one piece of paper and grass on the other. You could also do a bowl of water on one piece and fish on the other one. Or a bird on one piece and a tree on the other one for the bird to sit on.
  3. Tape both pieces of paper on either side at the end of a pencil. The pictures need to face outside.
  4. Now rub the pencils between your hands as if it was a stick that you want to light a fire with.
  5. Look at the pictures.
  6. You will see both pictures combined together, for example the rabbit sitting on the grass or the fish in the bowl.

The reason this works is that our eyes are too slow to follow the fast movement of the pictures and can only see a limited amount of pictures per second.

You can also watch this experiment as a video:

Static Electricity at Home

Background

When a balloon is rubbed against hair, a towel or a jumper, it gains more electrons which have a negative charge. This gives the balloon an overall negative charge. Objects with a positive charge or no overall charge like a tin can will now be attracted (= be drawn) to the balloon. We call this “static electricity”.

You will need

  • Balloon
  • Towel, jumper or your hair
  • Empty soda can
  • Water tap
  • A smooth surface, e.g. a table

What to do

  1. Blow up the balloon.
  2. Put the empty soda can on its side on a smooth surface.
  3. Rub the balloon on a towel, jumper or your hair to create static electricity.
  4. Hold the balloon close to the side of the soda can, but do not let them touch.
  5. Slowly move the balloon away from the soda can along the surface.
  6. Observe what happens.
  7. Rub the balloon again on a towel, jumper or your hair.
  8. Open the water tap, so that only very little water is running. It should be almost dripping.
  9. Hold the balloon close to the water, but do not let the balloon touch the water.
  10. Observe what happens.

You can also watch this experiment here: