I have got physics on the brain because I have been working hard on updating Physics for the Grammar Stage I can't wait to share the results with you all, but for this month's activity I thought I would bring back an oldie, but goodie post - the Great LEGO® Balloon Car race! 

We had so much fun with this science activity several years ago. It was inspired by this LEGO balloon car post by Mary at Homegrown Learners, so I won't repeat the directions in detail here, but the basic idea is to build a car out of LEGO bricks that has space for a balloon. Then, blow it up and see if it pushes the car.

The Science Behind the LEGO Balloon Car

The LEGO balloon car is basically a simple machine that uses wind power to move.

The wheels and axles act as simple machines. They reduce the amount a friction the vehicle experiences as it travels across a surface, which makes it easier to move.

Newton’s First Law of Motion states that an object will not move unless a force acts upon it. So, we have to have a force that pushes the car to get it to move. In the case of the LEGO balloon car, we are using a power source – the balloon!

When you blow up a balloon the elastic stretches, which creates a globe full of pressurized air. If you don’t tie off the end, the stretched elastic quickly forces the air inside out the tiny hole at the end of the balloon.

So, in the LEGO balloon car, the air escapes causing an equal but opposite reaction that pushes the car forward. The less our car weighs, the less friction or drag it creates and the faster it goes.

Now that we understand how the cars work, let’s get back to the race.

The Great LEGO Balloon Car Race

We had three cars in our race.

• #1 - The Blue Wonder (built by our 5 yo with a bit of help)
• #2 - Simple and Sleek (built by our 13 yo)
• #3 - The Red Menace (built by yours truly)

The race was intense and it lasted only 3 seconds! In the end, the winner was...

#2 - Simple and Sleek!!

My car, The Red Menace, worked well in testing, but when it came time to race every balloon I blew up popped.

The Blue Wonder was too fragile and keep falling apart before the race was even finished.

We had a blast with this project! Plus the kids both learned tons and are already making plans for the next LEGO balloon car race!