How to build a water rocket with a bike pump and water bottle

Ready to explore the thrilling world of physics and rocketry? With just a few household items, you can build your very own water rocket and launch it high into the sky! This exciting activity is perfect for budding engineers and scientists eager to learn about pressure, propulsion, and aerodynamics. So, grab a bike pump, a water bottle, and let's get ready for lift-off!

What You’ll Need:

• A sturdy plastic water bottle (1.25L or 2L works best)
• A bike pump with a needle attachment & hose
• A rubber stopper or cork that can snuggly fit in the bottles neck. Poke a hole through it so your pump needle attachment can firmly squeeze inside
• A box or mount to rest the bottle on while you pump
• Cardboard to decorate it
• Water (about 1/3 of the bottle’s volume)
• Safety goggles (safety first!)
• A large, open outdoor area for launching

It's our boy, Newton again!

Your water rocket works thanks to the principles of Newton's Third Law of Motion: "For every action, there is an equal and opposite reaction." When we use a bike pump to pressurise the air inside the bottle, eventually that pressure overcomes the friction of the rubber stopper, and forces the water down out of the bottom. This water creates a thrust that propels the rocket upwards. The more pressure you build up, the greater the thrust and the higher your rocket will fly.

This experiment also demonstrates how rockets in space work. Real rockets use controlled explosions to push fuel out at high speeds, which propels them in the opposite direction—just like your water rocket, but with a lot more power!

Step 1: Safety First!

Choose a safe launch site.

Find an open outdoor area, like a footy field, free from obstructions like trees or power lines. This will ensure that your rocket has plenty of room to soar.

Put on your safety goggles.

Before you start pumping, make sure everyone is wearing safety goggles and standing back from the launch area. The rocket will launch with a lot of force, so it's important to be cautious

Step 2: Prepare Your Rocket

Fill the water bottle.

Start by filling your water bottle about one-third full with water or less. (You can experiment with different volumes) This will be the "fuel" for your rocket. The more water you add, the heavier the rocket will be, so start with about a third and adjust for different flight results.

Attach the rubber stopper to the bike pump needle.

Connect the needle attachment to your bike pump by either forcing it through or poking it with something sharp first. Carefully insert the needle into the hole in the rubber stopper. This setup will allow you to pressurize the air inside the bottle, creating the force needed to launch your rocket.

Insert the rubber stopper into the bottle

Take your rubber stopper and firmly insert it into the mouth of the bottle. Make sure it’s snug so no air can escape around the edges. it should be snug enough that you can pressurize the bottle, but not too tight that it can't release itself.

Step 3: Launch Your Rocket!

Start pumping air into the bottle.

Begin pumping air into the water bottle using the bike pump. As you pump, the air pressure inside the bottle will increase, pushing down on the water. Keep pumping until the pressure builds up enough to overcome the friction of the rubber stopper.

Watch the launch!

As the pressure inside the bottle builds, the water will be forced out of the bottle with great force, pushing the bottle upwards. When the pressure is high enough, the stopper will pop out, and your rocket will blast off! The water shooting out of the bottle provides the thrust needed to propel the rocket into the sky.

Observe the flight.

Watch as your rocket soars high into the air! Notice how the angle and amount of water can affect the height and distance of the launch. Try experimenting with different amounts of water and different pump pressures to see how they change the rocket’s flight.

Step 4: Experiment and Have Fun!

Now that you’ve mastered the basics of launching your water rocket, it’s time to experiment and see how different variables affect your rocket’s flight. Here are some ideas:

Change the water level.

Try launching with different amounts of water in the bottle. Does more water make the rocket fly higher, or does it slow it down because of the extra weight?

Adjust the launch angle.

Prop your rocket up at different angles and see how it affects the distance and height of the flight. A slight angle might make the rocket travel further, while a straight-up launch could maximise height.

Design fins for stability.

Add some cardboard fins to your rocket to help it fly straighter. How do different fin shapes and sizes affect the rocket's stability and trajectory?

Building and launching a water rocket is a thrilling way to learn about physics and engineering. By experimenting with pressure, propulsion, and aerodynamics, you’ve explored some of the same principles that scientists use to send rockets into space. So keep experimenting, keep learning, and who knows,maybe one day you’ll be designing rockets that go beyond the sky!

Happy launching!