Newton's second law - forces and acceleration
Newton's second law states that if you exert a constant force on an object it will speed up or slow down (accelerate). You can see this for yourself with the help of a friend and a bike.
You will need:
A friend
A bike or skateboard
Open space
- Find a large open space, but be careful of traffic and other people.
- Get your friend to sit on the bike or skateboard.
- Push your friend along carefully. Try to do this with a constant force. Your friend must not pedal or use the brakes. If you have got a spring that is strong enough you can attach one end of the spring to the bike while you pull them along with the other end. Make sure that the extension on the spring stays constant so you know you are pulling with a constant force.
- Keep pushing (or pulling) and see what happens to your speed. You should find that if you started off walking you have to walk quicker and quicker, and eventually run, to keep your force constant. This is a demonstration of constant force resulting in acceleration.
What happens to your friend's speed when you stop pushing? Does he or she speed up, slow down, or stay the same? You should find that your friend slows down, so there must be force acting on him or her.
It's friction again. Can you work out where the friction is acting? There is friction from the air, in the bearings of the axles and the wheels against the floor.