Combining elements of science, technology and maths it is a useful vehicle for giving pupils a taste of engineering and helps them to understand how things work. It also demonstrates Isaac Newton’s third law of motion: “For every action there is an equal and opposite reaction”

What you’ll need

Step 1

Using the metal rule and felt tip pen mark out a rectangle 10cm (W) x 16.5cm (L) on corrugated plastic sheet. Cut out the rectangle with the cutting knife and rule to make the buggy base.

Step 2

Measure, mark and cut four 4cm lengths of straw using the rule, pen and scissors. Measure and mark two 14cm lengths of wooden rod, and cut them off using the junior hacksaw and vice. Smooth with sandpaper so that they will run smoothly in the straw bearings and the wheels will go on. Slide two lengths of straw onto each axle, then push a wheel onto each end of the wooden rod. TIP— Use a strip of masking tape to hold the straws in place while gluing.

Step 3

Mark two lines 2.5 cm long on the buggy base 2 cm from one end. Run glue along each line as shown, and then attach the axle before the glue hardens. The straws should overlap each edge by roughly 0.5cm, so the wheels can’t touch the base edge. Don’t get glue on the axle, as this will stop it rotating. Remove the masking tape. Try spinning the wheels to check the axle spins freely; if the wheels are pushed tight against the ends of the straw then move them out along the axle. Reinforce the joint with lengths of masking tape as shown and repeat for the second axle.

Step 4

Turn the buggy over. Measure and mark 21cm of hose, and cut. Put a thick line of glue about 5cm long along the middle of the buggy and stick the hose on firmly so that it overlaps the buggy base at both ends. TIP – The hose is normally curved; stick it with the ends curving upwards so that the balloon doesn’t rub on the floor while moving.

Step 5

Slide the neck of the balloon over one hose end, and blow it up through the other. Pinch the neck of the balloon between your fingers just in front of the hose, or put your thumb over the open hose end, place the buggy on the floor and let go; you could try this on different surfaces. Why not use coloured feathers, shells etc. as decoration?

How else you can use the buggy?

• Compare how far the buggy goes when you try different balloon shapes, sizes and types or blow them up by different amounts. Consider modifying your design to keep the inflated balloon from touching the floor.
• Use tubes of different diameters to see if it affects the range and speed of the buggy.
• You can use your buggy to demonstrate energy storage and transfer, forces and motion, friction and reducing friction.
• Why not remove the balloon, put the buggy on a ramp and use a protractor to measure the ramp angle at which it starts to roll? You can then tape the middle of the axles to the buggy base to stop them rotating, and compare the angle at which the buggy starts to slide down, to compare rolling resistance with sliding resistance.
• Finally you can cut tyres from bicycle inner tubes or balloons, stretch them over the wheels and compare the angle at which the buggy slides with tyres. This demonstrates why cars have rubber tyres to help them grip the road!

About our guest author

Caroline Alliston, is a professional engineer and technical author with a degree from Cambridge and twenty four years experience in industry. Whilst on a career break to spend more time with her two boys, she started a club at their school to enthuse children about science and engineering. Before long there were more children on the waiting list than in the actual club!

Caroline now spends her time running hugely popular workshops for teachers, pupils, home educated children, holiday clubs, Scout groups etc. Unable to be in three places at once, she has written the Technology for Fun series of books incorporating her favourite and most successful projects, to give even more children the opportunity to have fun making things that really work.