Water-powered Car 1 (High Water Level)

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What type of experiment is this?

Experimental procedure and explanation:

• Let’s make a toy called a water-powered car. This car runs using the energy from the height of the water, known as potential energy.
• First, connect a vinyl hose to the water tank. (In this video, the hose is connected at the middle of the tank using a rubber balloon.)
• To increase the height of the tank, create a support structure using a plastic bottle or a similar item. Secure the end of the hose to the rear of the car body.
• Fill the tank with water while holding the hose outlet closed with your finger. When you release your finger, water flows out, and the car begins to move.
• This movement demonstrates the principle of “Jet Propulsion”: As water is forcefully expelled backward, the reaction force (Newton’s third law of action and reaction) pushes the car forward, generating the propulsive force.
• The magnitude of the propulsive force depends on both the flow velocity (the speed at which water flows out of the hose) and the flow rate (the volume of water flowing out per unit time). The propulsive force can be expressed as
  (Propulsive force) = (water density) × (flow velocity) × (flow rate).
• As demonstrated in the experiment “The Height of Water and Its Energy,” increasing the height of the water level in the tank increases the flow rate at the outlet. This means that the higher the water level, the greater the flow velocity and flow rate, resulting in a stronger propulsive force.
• It might be fun to limit the amount of water each person can use and compete to see whose water-powered car can go the fastest or travel the farthest.
• This video was produced with the support of the JSPS Grant-in-Aid for Scientific Research (18K03956).

[Keywords]	Jet propulsion, potential energy, law of momentum, action–reaction
[Related items]	Jet Propulsion, The Height of Water and its Energy, Water-powered Car 2
[References]	Ryozo Ishiwata and Mitsumasa Nemoto, “The Wonder of Flow,” Kodansha Bluebacks, pp. 98–101, pp. 114–117. Ryozo Ishiwata, “Illustrated Fluid Dynamics Trivia,” Natsume Publishing, pp. 156–157, pp. 192–193.

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