Soap boat

A boat sails thanks to soap!

5 minutes
Experiment's video preview



  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

My boat isn’t moving. Why not?

Try to spread the sides of the boat so that there is a gap between them. This should help the boat move. And, of course, make sure the water in the bowl is clean.

My boat stopped moving, even though it was moving well before.

Don't worry, this is normal! Wash the boat and change the water in the bowl in order to continue. Or try repeating this experiment on larger bodies of water, such as a bathtub.

Step-by-step instructions

Put the boat on the surface of water.


Make the boat move using nothing but soap.


See how long the boat can go on just one drop of soap.


Wash the boat and change the water to repeat. Run the boat on larger bodies of water, like a bathtub or a pond. Organize a race!



Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

Why does the boat start moving when soap is added?

Water molecules H2O are attracted to each other quite strongly. Any object placed on the water's surface, like our boat, also experiences this attraction, but this force pulls such an object equally strongly in all directions and the object won't move.

Soap is really good at reducing water's intermolecular forces. Simply reducing the pull on the boat from all sides won't do much, but what if we reduce this force on only the rear side of the boat? The water will still pull the boat strongly forward, but much less so in the opposite direction. In other words, the water at the front will win this "tug-o-war", causing the boat to surge forward.

This peculiar method may not be very effective for larger vessels, but some small aquatic bugs can move as fast as 17 cm per second using it.

That's interesting!

What is jet force?

Jet force is a force that results from the separation of one part of a system from another. This force pushes one way, moving the separated component the other way. In the case of a rocket, jet force is caused by an engine that pushes hot gases to the bottom of the rocket engine (towards the ground) opposite the movement of the rocket (away from the ground).

The gas is burned, and the resulting energy is used to propel the rocket upward. The burning particles of gas bounce vigorously off the surface of the engine, pushing it forward. The gas is very hot, the molecules move very fast, and the momentum (the characteristic connecting the velocity and mass of the object) of the gas molecules is significant – enough to push the rocket forward.

During a launch, it would seem that the rocket is lifted off the ground by the flow of matter from the nozzle, but in fact, the driving force is always the pressure created by hot gas on the surface of the engine nozzle. After all, if a rocket could only use the Earth to propel itself forward, how would it then move in outer space?

How do animals use jet propulsion?

Squids, octopuses, and bivalves all move using methods based on the reactive principle. Squids and octopuses gather water into the hood under their tentacles and release it in one brisk movement, propelling themselves in the opposite direction from the water molecules they eject. Scallops also move reactively, but with the help of other organs – they slam their shell shutters with the help of a special trigger muscle in order to eject a stream of water.