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Exercise isn鈥檛 just good for your body, it鈥檚 good for your brain 鈥� and it makes you feel good too. One way of measuring how active you are is to wear a pedometer for a day.

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Pedometers are devices that register every time they鈥檙e bumped, as they are every time you take a step. So if you wear one, they count up how many steps you鈥檝e taken. Pedometers can be inexpensive, so this is something you can try for yourself. But watch out - step-counting can be addictive!

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In our experiment, we found that the boys who had worn a pedometer for a few hours had been more active than the girls. The reason for this seemed to be that during lunchtime the boys played football, while the girls were more likely to stand around chatting! Our scientist Fran Scott explained that this is what some researchers also found when they did this experiment. They found that at around age 8, boys and girls take the same amount of exercise, but once they get to 14, boys take more exercise than girls.

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So come on girls, don鈥檛 just stand there - get moving!

For this demonstration you鈥檒l need a large ball, like a basketball, and a tennis ball.

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Try dropping each one from shoulder height to see how high it bounces normally. Now balance the tennis ball on top of the basketball, and by just holding the basketball, drop them at the same time. You should find the tennis ball pings high into the air 鈥� far higher than it did by itself 鈥�

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What鈥檚 happening?
It鈥檚 all to do with something called 鈥渕omentum鈥�. Momentum is a measure of how heavy something is, and how fast it鈥檚 going. When you dropped the balls, they both accelerated downwards, due to gravity. However the basketball - because it started underneath the tennis ball - would hit the ground first.听 This means it would have bounced on the ground and be on its way back up while the tennis ball was still falling. This means the balls would crash together in mid-air and as they crash some of the basketball鈥檚 momentum would be passed onto the tennis ball. Now, because the tennis ball is much lighter than the basketball, this means the tennis ball would leave the collision travelling much faster, and this is why it pings high into the air.

Muscles make your body move 鈥� but as you鈥檒l see, sometimes they can make your body move in a way you weren鈥檛 expecting!

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What to do:
Stand in a doorway (best option), or side on to a wall, a footstep away from it. Now push hard against the doorway or the wall with the backs of your hand(s).听 Push for 30 seconds.
Now step away from the doorway or the wall, and see what happens. You should find that your arm(s) float up into the air, seemingly out of your control.

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As Dick and Dom discovered, you can also get your leg to float up, if you position yourself sideways against the wall again, and this time push against the outside of one foot. This is trickier to do, but still very entertaining!

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What鈥檚 happening?
Normally when you make a muscle move, a message goes from your brain to the muscle, and a chemical is released into your muscle that makes it get shorter and move. When you do this activity, and push against the wall, your brain sends more and more of the chemical into the muscle, but the muscle has nowhere to go because it鈥檚 up against the doorframe or wall. When you step away, all of that chemical is still hanging around your muscle, so it makes the muscle move even though your brain is no longer telling it to鈥� making your arms rise up, as though they鈥檝e got minds of their own!