First up, is an experiment with tennis balls and if you try it, we promise you won’t get tennis elbow!

What You Need:

• Normal, rubber tennis ball
• Sponge tennis ball – the same size
• Your hands!
• An unsuspecting victim – parents always make good experiment victims!

What You Do:

1. First, ask your ‘victim’ to feel the difference in weight between the two balls.
2. Next, hold the rubber tennis ball in your left hand and hold the sponge tennis ball in your right hand.
3. Stretch your arms out straight in front of you with your palms facing the floor, whilst still holding the balls.
4. Ask your ‘victim’ which ball will hit the floor first. Your victim will probably reply that they think the rubber ball will hit the floor first because it is heavier than the sponge ball.
5. Release the balls from your hands at the same time.
6. To the astonishment of your ‘victim’, the balls will hit the floor at roughly the same time!

What’s Going On?

Light and heavy objects all fall at the same rate. It’s all to do with how the force of gravity behaves. Galileo was probably one of the first thinkers to look closely at how things fall to the earth. He was born in 1564, in Pisa, Italy. There is a story that says he climbed to the top of the Leaning Tower of Pisa, with two cannonballs. The cannonballs were the same size but one was lighter than the other. The story goes that Galileo dropped the two cannonballs over the side of the tower to prove that they would hit the earth at the same time. Let’s just hope there was no-one standing underneath while he was doing this experiment!

Last month, Hay-Wire received this science stumper from one of our subscribers:

Thanks for your question, Gerry! Let’s get the ball rolling for an answer...

Underneath the yellow fur, a tennis ball is made from rubber and it is hollow inside. The air inside the ball is at a slightly higher pressure than the air outside the ball. The higher air pressure makes the ball bouncy because when the ball hits the floor, it pushes the side of the ball inwards. The rubber wants to return to its original round shape so it pushes back against the floor. The result propels the ball upward and into the air. The higher pressure inside the ball speeds up this process so the tennis ball bounces even higher.

As tennis players hit the balls, the air inside the balls escapes – making them less bouncy. This is why you often hear tennis players shouting for “New balls!” throughout the game.

WARNING: Don’t cut open a tennis ball to see for yourself because you could hurt yourself.

If you’ve got a science question that you’d like Hay-Wire to answer in a future issue then please email: Hay-Wire.Clubhouse@nesta.org.uk with ‘SCIENCE STUMPER’ as the subject.

Take your mind off tennis for a moment and think back to the last issue of Hay-Wire. During National Bike Week, Hay-Wire offered you the chance to win a bicycle safety set which included a Storm cycle helmet, a bike light set and a reflective bib.

The draw took place yesterday and the lucky winner is: Hayley Dear, so expect your prize in the post soon!

Congratulations!