Summary: build and race lego cars with this idea that invites plenty of design and engineering and encourages a variety of different possible solutions
Set-up: 2 minutes
Play: 30 mins – several hours and many repetitions!
Complexity: medium, but younger children can easily be supported to achieve this
- A variety of lego bricks and wheels
- A balloon for each child
- Tape measure for extension activity
What to do
Suggest the idea to your child: What do they think, is it possible to make a balloon-powered car out of lego? How would it work? (How would the balloon actually power the car?) Once children have figured out that they will need to be able to blow the balloon up while it is attached to the car, they are partway to a solution. They now need to build a car and then find a brick that will attach the balloon (window or handle pieces are good). Support younger children by building a car alongside them and letting them observe your solution to the problem.
Try out your inventions. Does the car go? How far? What could your child change to make it work better? Prompt your child to think about changing the shape, colour or size of both the car model and the balloon. Explain that this is how engineers work, by creating prototypes, testing them out, and modifying them to improve them.
Try the cars on different surfaces (lino, carpet, wooden floors etc.). Does your child think it will go faster or slower on this floor? Do they know why? Talk about the friction that occurs when two surfaces (the lego wheels and the floor surface) rub up against each other.
Experiment with blowing the balloon up more and less – what do you notice?
Which car can go the furthest? Measure the distance of different models.
Learn the science behind the activity: Newton’s first and second Laws of Motion state that an object at rest stays at rest until a force is added – in other words, until it is pushed, or put into motion, the lego car stays at rest. When you blow up a balloon, you fill it with air/gas. When you let go of the balloon, you release the gas which escapes creating a forward pushing motion called thrust. Thrust is created from the energy released from the balloon. This is because of Newton’s third law of motion: for every action, there is an equal and opposite reaction. In other words, when the gas is forced out of the balloon, it pushes back against the air outside the balloon, which pushes the balloon forward.