Pedal power
Riding a bicycle is a perfect way to find out about force. When you are moving at a steady speed the force produced by your legs exactly balances friction, the force that tries to slow you down. You can never get rid of friction, but you can reduce it by keeping the bike oiled and your head down so that you lessen the friction caused by the air you push of the way.

1. Going up
When you go uphill, you have to counteract the downward force of gravity. The bike starts to slow down unless you put in extra work to match the downward pull.

2. Going down
Going downhill is easy, because this time gravity is on your side. If you freewheel and keep your hands off the brakes, the bike starts to speed up. It keeps speeding up until friction matches the pull of gravity.

3. On the level
On flat ground, gravity has no overall effect. To keep going at a steady speed, all you have to do is match the force of friction. Some of the friction is produced by the moving parts of the bike. The rest of it is produced by the air you push out of the way. If you go really fast, 'air resistance gets very large.

4. Time to Stop
As soon as you stop pedalling, friction and air resistance gradually bring the bike to a halt. Another form of friction, jamming on the brakes, stops the bike much more quickly.

FORCE AND MOTION

Force are at work all around us. They provide the push that gets things moving, but also include friction, the force that slows them down. They can make a jumbo jet hurtle down a runway and into the skies, or pull a snowflake towards the ground. Forces can also make things change direction, and they can stretch, squash and bend them out of shape. We cannot see forces themselves, but we can see and feel what they do.

How does gravity work?
We know what gravity feels like, but it is still a mysterious force.Everything in the Universe, even your own body, attracts other objects toward it. When you stand on the ground, the Earth attracts your body and your body attract the Earth. Because the Earth is so huge, its gravitational pull keeps you on the ground.